A power distribution system includes all parts of an electrical system between the power source and the customer’s service entrance. It includes overhead and underground transmission methods and the equipment required for the control and protection of the system and personnel. The power source may be a local generating plant. Or it may be a high-voltage transmission line feeding a substation that reduces high voltage to a level suitable for local distribution.

 

 

 

Contents

1.0.0 Introduction

2.0.0 Safety in Power Distribution

3.0.0 Distribution Systems

4.0.0 Control and Protective Devices

5.0.0 Underground Considerations

6.0.0 Personal Protective Equipment and Hot Line Tools

 7.0.0 Installation of Overhead Distribution Equipment

8.0.0 Underground Distribution Systems

9.0.0 Test of Power Distribution Systems

10.0.0 Maintenance of Distribution Systems

Review Questions


1.0.0 INTRODUCTION

This manual is  mainly concerned with the overhead distribution system. Generally speaking, an overhead distribution system can be installed and maintained more efficiently than an underground system. Also, for equivalent conductor size, an overhead system has higher current capacity and offers greater flexibility for changes.

Here you will learn about line work safety and the tools and equipment a lineman uses. You will learn the basics in constructing and maintaining a power distribution system as well as the component parts of the system.

 

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2.0.0 SAFETY in POWER DISTRIBUTION

Safety is the most important topic covered in this course. The potential for an accident is present during all construction and maintenance operations but is much greater for crew members working on power distribution systems.

HIGH VOLTAGE in your work area calls for heightened awareness of the potential for serious injury or death caused by carelessness and of the necessity of taking precautions to ensure the safety of all personnel.

2.1.0 Equipment Requirements

Cranes, earth augers, bucket trucks, and line trucks with booms capable of contacting HIGH VOLTAGE lines because of their height must be operated with caution. Maintain a minimum separation of 10 feet between the equipment and the energized power circuits at all times. The equipment must be maintained in first-class mechanical condition. SAFETY FIRST must be the primary goal.

2.2.0 Personnel Safety

It is the line crew’s responsibility to ensure the SAFETY of all personnel working on power distribution lines, and observe the following safety precautions:

Many other safety procedures are required on the job—too many to list here. The Lineman’s and Cableman’s Handbook and Occupational Safety and Health Administration (OSHA) instructions are a courpoe of the references you need to learn more about job safety.

 

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3.0.0 DISTRIBUTION SYSTEMS

A power distribution system includes all parts of an electrical system between the power source and the customer’s service entrance. The power source may be either a local generating plant or a high-voltage transmission line feeding a substation that reduces the high voltage to a voltage suitable for local distribution. At most advance bases, the source of power will be generators connected directly to a load.

You will construct, maintain, and repair distribution systems. Depending on the type of system, the distribution system will consist of some combination of the following components, substations, distribution transformers, distribution lines, secondary circuits, secondary service drops, and safety and switching equipment. The distribution system may be underground, overhead, or a combination of the two.

3.1.0 Distribution Substations

Distribution substations change the transmission or generator voltage to a lower level, providing voltage sources for the distribution circuits supplying power to the customers.

Substations may be attended by operators or designed for automatic or remote control of the switching and voltage regulating equipment. Most large new substations are either automatic or remotely controlled.

3.2.0 Distribution Transformers

A distribution transformer is an electrical transformer used to carry electrical energy from a primary distribution circuit to a secondary distribution circuit. Distribution transformers are installed in the vicinity of each customer to reduce the voltage of the distribution circuit to a usable voltage, usually 120/240 volts.

Long-distance transmission of electricity requires a voltage higher than normally generated. A step-up transformer is used to produce the high voltage. Most electrical equipment in the Navy uses 120/208 volts. The primary voltage distributed on Navy shore installations, however, is usually 2,400/4,160 and 13,800 volts. A distribution transformer (step-down) is required to reduce the high-primary voltage to the utilization voltage of 120/208 volts. The various types of transformer installations are discussed later in this course.

Regardless of the type of installation or arrangement, transformers must be protected by fused cutouts or circuit breakers, and lightning arresters should be installed between the high-voltage line and the fused cutouts.

Three general types of single-phase distribution transformers are in use today. The conventional type requires a lightning arrester and fuse cutout on the primary-phase conductor feeding the transformer. The self-protected (SP) type has a built-in lightning protector; the completely self-protected (CSP) type has the lightning arrester and current- overload devices connected to the transformer and requires no separate protective devices. Figure 1 is an example of a bank of 3 conventional type distribution transformers.

Figure 1 – Conventional type distribution transformers.

3.3.0 Distribution Circuits

Distribution circuits (primary main circuits) originate from the distribution substation. Primary mains carry over 600 volts, but generally they operate between 2,400 and 34,500 volts. Primaries can be found in single-phase or three-phase configurations and generally operate as three-phase, three-wire or three-phase, four-wire circuits.

3.4.0 Secondary Circuits

Secondary circuits (secondary mains) originate from the secondary windings of a distribution transformer and are 600 Vac or less. The secondary circuits are also configured either delta (A) or wye (Y) and are also used for the same type of loading as the primary circuits.

Secondary circuits are either three phase — meaning they have three live conductors— or single phase, which can be one or two live conductors and a neutral.

3.4.1 Delta Configuration

The delta system is a three-phase, three-wire system configuration. The symbol for the delta configuration is "D". Only one voltage exists in a delta system. This voltage is obtained between any two of the three phase conductors in the system. This is a phase- to-phase connection and is therefore a LINE voltage. Since there is no neutral in a delta system, there is no potential from any energized phase to neutral or ground as long as the delta system remains pure (no grounds). The delta type (A) system, Figure 2, is used when most of the load in an area is commercial, consisting of motors and other three-phase equipment.

Figure 2 – Three-phase delta (A) primary and secondary system.

3.4.2 Wye Configuration

This system configuration is a three-phase, four-wire system and is the preferred system used by our military services. The symbol for the wye configuration is “Y ". The wye system has two voltage potentials: LINE and PHASE. Phase-to-phase (LINE) voltage is obtained between any two of the three energized phases. Phase-to-neutral (PHASE) voltage is obtained from any one of the three energized phases and the neutral conductor. The energized phases are designated with the first three letters of the alphabet: A, B and C (This phase designation applies to all systems). The neutral conductor is the fourth wire of this system and is designated with the letter N.

The neutral is connected to the ground at predetermined locations to ensure that it remains a de-energized conductor. The earth also serves as an alternate path back to the voltage source if the neutral conductor should break its path. The neutral is not an energized conductor, but should be treated as such since accidental opening of the conductor causes current to flow. The wye (Y) system, Figure 3, and is used primarily for residential use and where lighting makes up a substantial portion of the load.

Figure 3 – Three-phase wye (Y) primary and secondary system.

3.5.0 Service Drops

A service drop is the combined conductors used to provide an electrical connection between a secondary distribution circuit and a user's facility. There are different ways of installing the service drop. Some typical secondary racks used to install service drops are shown in Figure 4. Whether a rack has individual conductors or self-supporting service cable, known as triplex or quadraplex, to provide a service drop, you must maintain the minimum aboveground distance recommended by the NEC©. As shown in Figure 5, this distance is 12 feet over lawns, driveways, or walkways accessible to pedestrians and 18 feet over roads or alleyways subject to truck traffic. When the nearest distribution pole is over 125 feet from the facility to be connected, you must provide an intermediate support pole.

Figure 4 – Secondary racks and dead-end spools


Figure 5 – Minimum ground clearances of service drops.

3.6.0 Circuit Designs

3.6.1 Radial Distribution System

Figure 6 shows a representative schematic of a radial distribution system. Note that the independent feeders branch out to several distribution centers without intermediate connections between feeders.

Figure 6 – Radial distribution system.

The radial distribution system is the most frequently used system because it is the simplest and least expensive to build. Although operation and expansion are simple, it is not as reliable as most systems unless it uses quality components. A fault or loss of a cable, primary supply, or transformer will result in an outage on all loads the feeder serves. Furthermore, electrical service is interrupted when any piece of service equipment must be de-energized to perform routine maintenance and service.

You can improve service from this type of feeder by installing automatic circuit breakers that reclose the service at predetermined intervals. If the fault continues after a predetermined number of closures, the breaker will lock out until you clear the fault and restore service by hand reset.

3.6.2 Loop/Ring Distribution System

The loop, or ring, system of distribution starts at the substation and is connected to or encircles an area serving one or more distribution transformers or load centers. The conductor of the system returns to the same substation.

The loop system, Figure 7, is more expensive to build than the radial type but is more reliable. It may be justified in an area where continuity of service is of considerable importance, for example, a medical center.

Figure 7 – Loop, or ring, distribution system.

In the loop system, circuit breakers sectionalize the loop on both sides of each distribution transformer connected to the loop. Pilot wire relaying or directional overcurrent relays ordinarily control the two primary feeder breakers and the sectionalizing breakers associated with the loop feeder. Use pilot wire relaying when there are too many secondary substations to obtain selective timing with directional overcurrent relays.

When there is a fault in the primary loop, the breakers in the loop nearest the fault clear it, and the system breakers supply power the other way around the loop without interruption to most of the connected loads. Because the load points can be supplied from two or more directions, it is possible to remove any section of the loop from service for maintenance without causing an outage at other load points. If a fault occurs in a section adjacent to the distribution substation, the entire load may have to be fed from one side of the loop until repairs provide sufficient conductor capacity in the loop to permit operation without excessive voltage drop or overheating of the feeder when either side of the loop is out of service. If a fault occurs in the distribution transformer, the breaker in the primary leads clears it, and the loop remains intact.

3.6.3 Network Distribution System

The network and radial systems differ with respect to the transformer secondaries. In a network system, Figure 8, transformer secondaries are paralleled; in a radial system, they are not.

Figure 8 – Network distribution system.

The network is the most flexible type of primary system; it provides the best service reliability to the distribution transformers or load center, particularly when the system is supplied from two or more distribution substations. Power can flow from any substation to any distribution transformer or load center in the network system. The network system is more flexible with regard to load growth than the radial or loop system and is adaptable to any rate of load growth can extend service readily to additional points of usage with relatively small amounts of new construction. The network system, however, requires large quantities of equipment and extensive relaying; therefore, it is more expensive than the radial system. From the standpoint of economy, the network system is suitable only in heavy-load-density areas where the load center units range from 1,000 to 4,000 kilovoltamperes (kVA).

The transformers of a secondary network distribution system are connected in parallel through a special type of circuit breaker, called a network protector, to a secondary bus. Radial secondary feeders are tapped from the secondary bus to supply loads. A more complex network is a system in which the low voltage circuits are interconnected in the form of a grid or mesh.

If a primary feeder fails or a fault occurs on a primary feeder or distribution transformer, the other transformers start to feed back through the network protector on the faulted circuit. This reverse power causes the network protector to open and disconnect the faulty supply circuit from the secondary bus. The network protector operates so fast that there is minimal exposure of secondary equipment to the associated voltage drop.

3.6.4 Primary Selective System

In some instances, a primary selective system can provide a higher degree of reliability. A primary selective system can also provide protection against loss of a primary supply, as shown in Figure 9. Each unit substation is connected to two separate primary feeders through switching equipment to provide a normal and an alternate source. When the normal source feeder is out of service for maintenance or a fault, electrician switches the distribution transformer, either manually or automatically, to the alternate source. An interruption will occur until the load is transferred to the alternate source. The cost of a primary selective system is somewhat higher than that of a radial system because it duplicates primary cable and switchgear.

Figure 9 – Primary selective distribution system.

In laying out a distribution system for a base, divide the base into a number of sections. Choose the sections so that the load in each section is close to one of the distribution centers. Take this action to keep the length of the mains as short as possible and to keep the voltage drop low between the distribution and the loads. The distribution or load centers should be located as near the electrical load center as possible.

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4.0.0 CONTROL and PROTECTIVE DEVICES

4.1.0 Distribution Cutouts

A distribution cutout provides a high-voltage mounting for the fuse element that protects the distribution system or the equipment connected to it. Figure 10 shows an open type of distribution cutout. Installations of transformers, capacitors, cable circuits, and sectionalizing points on overhead circuits use distribution cutouts.

Figure 10 – Open type distribution cutout

4.1.1 Enclosed Distribution Cutout

In an enclosed distribution cutout, the fuse clips and fuse holder are mounted completely within an enclosure. A typical enclosed cutout has porcelain housing and a hinged door supporting the fuse holder. The fuse holder is a hollow vulcanized-fiber expulsion tube. The fuse link is placed inside the tube and connects with the upper and lower line terminals when the door is closed. When the fuse blows or melts because of excessive current passing through it, the resultant arc attacks the walls of the fiber tube, producing a gas that blows out the arc. The melting of the fusible element of some cutouts causes the door to drop open, signaling to the lineman that the fuse has blown. A fuse link cannot distinguish between a temporary or permanent fault. See Figure 11.

Figure 11 – Enclosed distribution cutout.

4.1.2 Open-link Distribution Cutout

This type of cutout differs from the open cutout in that it does not use the fiber expulsion tube. Spring terminal contacts support the fuse link. An arc-confining tube surrounds the fusible element of the link. During fault clearing, the spring contacts provide link separation and arc stretching. The arc-confining tube is incorporated as part of the fuse link.

4.1.3 Open Distribution Cutout

Open cutouts are similar to the enclosed types, except that they do not use housing. The open type is made for 100- or 200-amp operation. Some cutouts can be up rated from 100 to 200 amps by using a fuse tube rated for 200-amp operation.

4.2.0 Switches

A switch is used to disconnect or close circuits that may be energized. High-voltage switches remotely using a variety of mechanisms or manually. Depending on their purpose in the system and their physical makeup, switches are divided into three general classes: air, oil, and vacuum switches. These three classes can be further subdivided (depending on their function) into disconnects, circuit breakers, or reclosers.

4.2.1 Air Switches

As their name implies, air switches are switches whose contacts are opened and use air to insulate their contacts when current flow is interrupted.

An air-circuit breaker switch can have both blade and stationary contacts equipped with arcing horns. These horns are pieces of metal between which the arc forms when a circuit-carrying current is opened. These arc horns are drawn further and further apart until the arc finally breaks. Air-break switches are usually mounted on substation structures or on poles and are operated manually from the ground or automatically. In a three-phase circuit all three switches, one for each phase are opened and closed together.

An air-disconnect switch is not equipped with arcing horns or other load-break devices. It therefore cannot be opened while current is flowing. If the disconnect switch should be opened while current is flowing in the line, an arc would likely be drawn between the blade and its stationary contacts. The hot arc would melt part of the metal, thereby damaging the switch. The purpose of a disconnect switch is to isolate a line or a piece of equipment for the purpose of making the disconnected line or equipment dead electrically, thus making it safe for repairs, tests, or inspections.

4.2.2 Oil Switches

An oil switch is a high-voltage switch whose contacts open and close in oil. Oil switches may be used as disconnect, circuit breakers, or reclosers. The switch is actually immersed in an oil bath, contained in a steel tank. The reason for placing high-voltage switches in oil is that the oil may help to break the circuit when the switch is opened. With high voltages, a separation of the switch contacts does not always break the current flow, because an electric arc forms between the contacts. If the contacts are opened in oil, however, the oil helps to quench the arc. Oil is an insulator, therefore, helps to quench the arc between the contacts. The three lines of a three-phase circuit can be opened and closed by a single oil switch. If the voltage is not extremely high, the three poles of the switch are generally in the same tank. But if the voltage of the line is high, the three poles of the switch are in separate containers.

4.2.3 Circuit Reclosers

The circuit reclosers most commonly used in power distribution is electronic reclosers, oil reclosers, or vacuum reclosers. These reclosers all operate in essentially the same manner.

Reclosers come in single or three-phase models and can either be pole-mounted or installed in a substation. These reclosers provide overload protection and are designed to open a circuit in an overload condition and then automatically reclose the circuit. If the fault on the system has cleared, the recloser remains closed. If the fault has not cleared, the recloser trips again, and after a short interval, recloses the system for the second time. If the fault has not cleared on the third time, the system will open and stay open. The recloser also has a manual lever or electronic control to set the recloser on what is commonly referred to as "singleshot" action. When linemen are working in the general area of a circuit, they place the recloser in the singleshot mode. Then should a mistake occur, causing the circuit to trip, it will not reset itself automatically.

 

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5.0.0 UNDERGROUND CONSIDERATIONS

Electric distribution circuits have been installed underground for many years. Conventional underground systems employ some, if not all, of the following: conduits encased in concrete, manholes, ducts and trenches, direct burial cable and riser/potheads, underground power cables, and underground communication cables. After it has been determined that the load density is high enough to justify the expenses associated with an underground system, the system must be designed; and then construction may begin.

5.1.0 Manholes

Manholes, handholes, and vaults are designed to sustain all expected loads that may be imposed on the structure. The horizontal or vertical design loads consist of dead load, live load, equipment load, impact, load due to water table or frost, and any other load expected to be imposed on or occur adjacent to the structure. The structure should sustain the combination of vertical and lateral loading that produces the maximum shear and bending moments in the structure.

Manholes are necessary in a power distribution system to permit the installation, removal, splicing, and rearrangement of the cables. A manhole is merely a subterranean vault or masonry chamber of sufficient size to permit proper manipulation of the cables. Arranged on the sides of the vault are devices that support the cables.

The layout of the base to be supplied with power largely determines the location of manholes. Whenever a branch or lateral extends from the main subway, there must be a manhole, and there must be manholes at intersections of subways. In general, cables are not made in lengths exceeding 400 to 600 feet; and as it is necessary to locate splices in manholes, the distance between manholes cannot exceed these values. Furthermore, it is not advisable to pull in long lengths of cable because the mechanical strain on the conductors and sheath may become too great during the pulling-in process. Manholes should be located not more than 500 feet apart. The lines should preferably be run straight between manholes.

Manholes come in many shapes and sizes to meet the ideas of the designer and to satisfy local conditions. Figure 12 shows an example of a typical manhole. If there are obstacles at the point where a manhole is to be located, you must modify the form of the manhole to avoid them. The form approximating an ellipse, Figure 13, is used so that the cables will not be abruptly bent in turning them around in the manhole. When you use the rectangular type of manhole, Figure 14, take care not to bend the cables too sharply.

Figure 12 – Typical Manholes.


Figure 13 – Elliptical type of manhole.


Figure 14 – Rectangular type of manhole.

The size of a manhole will vary with the number of cables it can accommodate; but, in any case, there must be sufficient room to work in the manhole. A 5- by 7-foot manhole is probably the largest required in isolated plant work, while a 3- by 4-foot manhole is about the smallest. When a manhole contains transformers, the manhole is larger to allow for working space around the transformer and for ventilation. Allow about 2 or 3 feet of volume per kva of transformer rating.

Manholes are built of brick, concrete, or both. When many manholes of the same size are required and there are no subterranean obstructions, concrete are usually the cheapest and the best material. But when only a few are to be constructed or when there are many obstructions, a manhole with a concrete bottom, brick sides and a concrete top is probably the best. You can construct such a manhole without having to wait for concrete to set before you can remove the forms. There is a growing use of precast concrete manholes shipped directly to the project site.

Build a manhole with brick walls by first pouring the concrete floor and then building up the brick walls thereon. If the manhole is large, the roof can be either of steel-reinforced concrete or of brick set between rails. Probably for installations in which only a few manholes are to be built, the brick-between-rails method is the best. For a small manhole, no masonry roof is necessary, as the cast-steel manhole cover forms the roof.

Make cement mortar for building brick manholes or for conduit construction by mixing together 1 part cement, 3 parts sand, and about 1/3 part water, all by volume.

Build a concrete manhole by first pouring the concrete floor and then erecting the form for the sides. In a self-supporting soil, the sides of the hole constitute the form for the outside of the manhole. If the soil is not self-supporting, there must be an outer form of rough planks (plywood), which is usually left in the ground. Place steel reinforcing, such as old rails, in the concrete top of a large manhole. All reinforcing steel should be completely encased in concrete to prevent corrosion.

Manhole covers should always be made of cast steel and covers should be round so that they cannot drop into the hole accidentally.

So called watertight covers are seldom used now, as it is not feasible to make a satisfactory watertight cover at reasonable expense. Do not fasten down a cover because if you do, and accumulated gas in a manhole explodes, the vault and cover will shatter. Use a ventilated cover to allow gas to escape. The newer types of cover have ventilating slots over approximately 50 percent of their area. Dirt and water will get into the hole, but the dirt can be cleaned out and the water will drain out and no harm will result; however, if there is no ventilation, an explosion of gas may occur and do great damage.

Before entering any manhole, the vault must be ventilated to remove all toxic or explosive gases and ensure adequate oxygen for survival. Forced air ventilation, respiratory protection, an observer on the surface, and a safety harness and line may be required for safe entry. Consult your supervisor before entering any manhole.

When feasible, a sewer connection should lead from the bottom of every manhole. A strainer made of noncorrosive wire should protect the mouth of the trap. If you cannot make a sewer connection, there should be a hole in the manhole floor so that water can drain out. A pocket under the manhole filled with broken rock will promote effective drainage.

5.2.0 Ducts and Trenches

Duct line and manhole systems provide the best available underground system. Such a system allows for growth and permits cost-effective replacement of existing cables or cable terminations damaged by faults or made obsolete by aging. Concrete encasement provides the cables with minimum susceptibility to damage and optimum safety to personnel. Several types of underground ducts are in general use, such as fiber, wood, vitrified tile, iron pipe, asbestos composition polyvinyl chloride (PVC), and concrete.

An underground installation usually consists of several duct lines. Stagger joints between sections so the joints in several lines do not all occur at the same place. To ensure staggering, use starting sections of different lengths at the starting manhole. For duct set in concrete, there must be at least 3 inches of concrete around each line of duct. Where concrete encasement is specified, concrete should have strength of not less than 2,500 pounds per square inch when cured for 28 days. Use spacers like the one shown in Figure 15 to accomplish the 3-inch spacing. The upper lines of the duct must be a minimum of 3 feet below the ground surface.

Figure 15 – Spacing fiber duct in concrete.

The location of the trench varies according to ground condition. The trench should run as straight as possible from one manhole to the next. To ensure drainage, slope the line downward about 1 foot but never less than 3 inches every 100 horizontal feet. When one manhole cannot be located at a lower level than the other, the tine must slope downward from about the midpoint both ways toward the manhole, as shown in Figure 16.

Figure 16 – Slope for duct run.

Dig the trench to the desired depth and tamp the bottom hard to ensure a solid bed for the 3-inch bottom layer of concrete. Embed spacers in the bottom layer of concrete for a depth of about 1 inch before the concrete sets to ensure a solid base.

Burying cable directly in the ground is a widely used method for installations of single circuits for which the cost of duct construction would be prohibitive. Some of the more common applications of direct burial cable are as follows:

Both nonmetallic-armored cable and metallic-armored cable (parkway cable) are used for direct burial in the earth. The nonmetallic-armored types are lighter in weight, more flexible, and easier to splice and are not subject to rust, crystallization, induced sheath power loss, or trouble from stray currents. On the other hand, they do not give good protection against mechanical injury.

Direct burial of power cable is normally accomplished with a backhoe digging a trench large enough to permit bed preparation; whereas, communications cable is laid in a small trench created by a chain type of mechanical trencher. Install cables at a minimum depth of 30 inches for power cables of 600 Vac or over and 18 inches for communications cables. Installing cables at 30 inches or greater will protect them against extreme mechanical hazard, such as at street intersections or under roadways. Place the power cables in a 3-inch thick bed of sand. When backfilling a direct burial cable, place plastic streamers in the trench 12 to 18 inches above the cable. These streamers will alert future personnel conducting digging operations to the presence of the buried cable.

At intervals of 200 feet and at turns in the buried cable, you should also place small- concrete markers along the entire length. These precautionary signs help prevent some future human-related damages to the buried distribution systems. The marker should state the type of cable that is buried, such as power or communications, and the voltage or number of pairs.

Types UF and USE cables are code-designated single-conductor or multiconductor cables suitable for direct burial in the earth. The NEC® includes rules for the protection of underground conductors when the supply voltage exceeds 600 volts. These rules were introduced to minimize the hazards of “dig-ins.” Section 300.50 of the NEC® covers such rules.

5.3.0 Risers and Potheads

For connection of underground distribution circuits at any location, you must prepare the end for termination. In earlier times electricians accomplished this preparation with a pothead, as shown in Figure 17, but they now do it with special kits which provide plastic molds to be placed over individually prepared phases. The molds are poured full of epoxy. The new way is much more efficient and clean. Figure 18 shows the new style.

Figure 17 – Pothead.

Figure 18 – Diagram of a modern single- phase cable end termination kit.

Inspect the riser pole for underground distribution circuits when you inspect or maintain overhead lines, Figure 19. The inspection should include the disconnect switches or fused cutouts, the lightning arresters, the operation of the arrester ground leads isolation devices, the riser cables and potheads or termination, support of the cables, conduit or U-guard, and identification of the circuit and pole conditions.

Figure 19 – Riser pole for underground distribution circuit.

5.4.0 Underground Power Cables

Underground cables have various types of insulation and sheaths. Because higher voltages generate more heat, the amount of voltage carried determines the composition of the insulation.

Cables rated at 15 kilovolts and below usually have rubber or varnished cambric insulation and a PVC or rubber sheath. Those rated at 600 volts to 425 kilovolts have oil-impregnated paper insulation and a PVC sheath.

Cables rated at 5 kilovolts and above have metallic tape shields between the insulation and sheath for mechanical protection. Exceptions to this requirement are for single- conductor (1/0) cable with a PVC sheath and three-conductor (3/0) belted type of cable.

Much of the new cable being installed is crosslinked-polyethylene (XLP) or ethylene propylene rubber (EPR). These are called solid type of insulations. The size and number of conductors in the cable depend on the job requirements.

5.5.0 Underground Communications Cables

The most common types of underground communications cables in use today are steel- armored with plastic insulation, plastic insulated with aluminum armor, and the new shielded fiber-optic cables.

5.6.0 Pulling Cables

When installing a new run of duct, you pull in “pulling wire,” usually a lo-gauge iron wire. With this wire, you pull in a wire rope to which you attach the cable for pulling in.

Sometimes, when the duct has been in the ground a long time, the original iron pulling wire may be rusted so that it is not strong enough to pull the wire rope through. Also for a 400- to 500-foot run, it would be difficult to push a fish tape through the duct. You can simplify the job by using an air compressor to blow a chalk line cord through the duct.

To do this, take a small cloth and tie the chalk line end to the four comers, so the cloth functions like a small parachute. With the air hose in the end ofthe duct and the cord free to run out, you will be able to blow the cloth through to the next opening, even on a long run of duct.

Clean ducts by rodding. Quick-coupling duct rods (about 1 foot long and 1 inch in diameter) are connected together with a wire brush or other duct rod leader at the head to facilitate cleaning. Push the rods through manually or by means of power equipment. Leave a 12-gauge galvanized steel wire attached to the leader in the duct for the cable pulling crew.

Moisture inside a cable causes deterioration of the insulation; therefore take precautionary measures to avoid accumulation of moisture inside the cables. Before pulling a cable, ensure that the cable ends are sealed against moisture invasion.

5.7.0 Rigging

There are a number of ways to rig manholes for cable pulling. The most common method is using the winch on the truck and a pulling frame. See Figure 20.

Figure 20 – Manhole rigging for pulling cables.

Other methods include using a cable pulley attached to a timber block which, in turn, is supported by a wedge or by attaching the cable pulley to the manhole wall by means of an embedded eye. If you use this method, make sure that the lower sheave is in line and level with the duct in which you will pull the cable. To prevent injury to the cable by sharp edges, line the duct mouth with a shield.

When pulling cables into a long duct, use a feeding tube or bell for applying a lubricant at the duct mouth. Make sure you use the lubricant specified by the manufacturer of the cable.

Figure 21 shows a cable reel in proper position over the manhole so that the bend in the cable is not reversed as the cable is unreeled. All cable reels are marked with an arrow indicating the direction in which they must be rolled. Comply with this arrow when placing the reel at a manhole so that it turns in the proper direction as cable is pulled from the reel. Place the reel as near as practical to the manhole and raise it on reel jacks just enough to clear the ground.

Figure 21 – Reel in proper position.

5.8.0 Cable Installation

Assume that the winch line has been drawn into the duct, as the test line was pulled out. Now attach a basket grip to the end of the underground cable on the reel. Secure the end of the basket to the cable with a tight wrap of tape or wire. A swivel connection is necessary between the basket and the pulling cable to relieve twisting of the rope.

If the cable reel is within sight of the winch, it will take four people, in addition to the winch operator, to do the job safely. One person attends the reel to see that the cable rolls off the reel properly. Another in the manhole guides the cable into the duct. Both inspect the cable as it unreels and immediately signals “stop pulling” when a defect appears in order to make a closer inspection for possible damage to the sheath. A third stationed in the other manhole at the pulling end signals “stop pulling” when the cable appears. The fourth crew member, aboveground at the pulling-end manhole, relays signals to the winch operator. This procedure enables the winch operator to concentrate on his job of seeing that the winch line is wound onto the reel properly.

The speed for pulling cable into a duct varies with the length of the duct and cable sizes. You can successfully pull in a single cable at 75 feet per minute (fpm) in a clear straight duct. When you are handling more than one cable, reduce the speed to about 20 to 25 fpm, to prevent the conductors from crossing as they enter the duct.

When the “stop pulling” signal is given, make sure there is sufficient slack in both manholes for splicing or terminating the cable. Adjust the slack with the cable basket grip. Exercise care to prevent injury to the cable insulation. Remove the binding tape and the basket grip from the cable. Then cut the cable to the desired length and seal the cutoff end in the manhole unless splicing is done immediately. You must also seal the end of the cable remaining on the reel. In addition, check the seal on the end of the cable that has traveled through the duct, and reseal it if it has been broken from the strain.

5.9.0 Dangerous Gases

Gases may be dangerous for several reasons. The gas concentration may be explosive if it is made up of methane, sewer gas, natural gas, concentrations of spilled gasoline, or other liquid fuel vapors. As a general rule, these gases are heavier than air and will concentrate in low areas, such as manholes and ducts. They will remain there until they are dispersed. These gases are toxic as well as explosive. Other toxic gases are chlorine, ammonia, and a variety of the sulfide combinations. Still other gases deplete the oxygen in the manholes and duct systems. Lack of oxygen can be as deadly as explosive or toxic gases. For these reasons, underground structures must be tested before workers enter them. Figures 7-22 and 7-23 show two common types of test sets used for identifying carbon monoxide and combustible gases. Figure 22 shows a carbon monoxide tester and Figure 23 an explosimeter. Only personnel who are specifically trained and certified may conduct tests for safe entry. Before entering any underground structures the base confined space manager or the assistant must certify the area safe for entry.

Figure 22 – Carbon monoxide tester.

Figure 23 – Explosimeter.

 

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6.0.0 PERSONAL PROTECTIVE EQUIPMENT and HOT-LINE TOOLS

It is not always possible or practical to de-energize lines, so you need to have a way to safely handle energized conductors and equipment. Use hot-line tools and personal protective equipment in these circumstances. Knowing proper operation and maintenance of these tools and equipment are vital to job completion on energized lines.

It is mandatory that the shop supervisor inspect all the shop’s protective equipment every six months. Supervisors maintain records showing the inspection date, dates of moisture and electrical tests, and the date the next 6 month inspection is due. The purpose of this inspection is to ensure that the users of the rubber protective equipment are performing their inspections, but you must not depend upon the supervisor’s inspection to keep you safe. Always inspect each item of protective equipment before you use it.

6.1.0 Rubber Protective Equipment

6.1.1 Types

Electricians use two kinds of protective equipment when working with energized lines: personal rubber protective equipment that the electrician wears, and protective equipment installed on lines and equipment to protect personnel from accidental contact.

6.1.2 Color Coding Standard

The American National Standards Institute/American Society of Testing and Materials (ANSI/ASTM) categorize rubber protective equipment into five classes by setting the maximum working voltage and di-electric test voltage for each. The classes are identified by color, and rubber protective equipment will have a colored label stating the type, size and class of the equipment. The colored label identifies the class rating of the rubber protective equipment at a glance. See Table 1.

Table 1 – ANSI/ASTM color codes.

Color Code Class Proof Test Voltage Max. use Voltage - AC
AC DC Ph to Ph Ph to Grd
Red 0           5,000 20,000          1,000               600
White 1 10,0000 40,000          7,500          4,4000
Yellow 2 20,0000 50,000 17,0000 10,0000
Green 3 30,0000 60,000 26,5000 15,0000
Orange 4 40,0000 70,000 36,0000 20,0000

6.2.0 Personal Rubber Protective Equipment

Rubber goods can be manufactured from natural rubber, which is called Type I, or from synthetic rubber, called Type II. Type II rubber goods are more prevalent because they are less susceptible to deterioration from corona, ozone, aging and weathering. Both types of rubber are susceptible to chemical deterioration from heat, sun, and especially petroleum products. Signs of chemical deterioration are: checking, swelling, softening, hardening or becoming sticky. At the first sign of chemical deterioration, the equipment should be removed from service.

6.3.0 Rubber Gloves

The most important article of protection for linemen or cablemen is a good pair of rubber gloves with the proper dielectric strength for the voltage of the circuit they will work on. Rubber gloves are used for intentional contact with energized lines while performing tasks, and must be rated at or above the voltage of the system on which they are being used. Leather gauntlets are worn over the gloves at all times to protect them from damage. These gauntlets must be 2 inches to 5 inches shorter than rubber glove length, depending upon system voltage. While using rubber gloves, use glove dust (100% talc powder) or cotton glove inserts to avoid skin irritation and prevent the rubber from sticking to your skin. See Figure 24.

Figure 24 – Rubber gloves, leather gauntlets and canvas bag.

Inspect rubber gloves inside and out before each use. You must also give them a field air test before each use. Accomplish this by pinching the open end closed and rolling it toward the fingers. This will trap air inside the glove. Roll the end until the fingers and palm expand, then hold the glove close to your face. Look, listen and feel for air leaking, indicating damage (fine tear, pin hole). Electrically test rubber gloves upon receipt and every 3 months thereafter if in use. If the gloves are stored on a shelf, test them every 12 months. If you find any defects during any inspection or test retire the gloves from service by cutting off one of the fingers.

Store rubber gloves in a canvas glove bag (seen in Figure 24) 2 inches longer than the rubber glove length. Never store gloves folded or inside out. Gloves must be clean and dry when stored; if they make contact with any chemicals, especially petroleum based chemicals such as hydraulic fluid, grease or oil, wipe down the gloves as soon as possible after the contact.

The ANSI standard ANSI/ASTM D120, Standard Specification for Rubber Insulating Gloves, covers lineman’s rubber glove specifications.

6.4.0 Rubber Sleeves

Linemen working on high-voltage distribution circuits must wear rubber sleeves in conjunction with rubber gloves to provide protection for arms and shoulders against incidental contact with energized surfaces. Inspect sleeves inside and out before each use. Stretching and rolling the sleeves on a flat surface will assist in finding defects. Electrically test sleeves every 12 months. If you find defects during any inspection or test, remove the sleeves from service.

Store sleeves clean and dry in a canvas bag or rolled up (not folded) to protect against mechanical and chemical damage. See Figure 25.

Figure 25 – Rubber sleeves.

6.5.0 Rubber Insulating Line Hose

Linemen can cover primary distribution conductors with rubber insulating line hose to protect themselves from an accidental electrical contact, Figure 26. The line hoses are manufactured in various lengths with inside-diameter measurements of 1 to 1 l/2 inches. They are split lengthwise to facilitate installation, and designed to be fitted together end-to-end.

Figure 26 – Line hose.

Inspect hoses inside and out before each use. Any cuts or abrasions deeper than one-quarter of the thickness of the rubber are unacceptable. Electrically test hoses upon receiving them from the manufacturer and retest them every 12 months.

The lineman should be sure that the voltage rating of the line hose provides an ample safety factor for the voltage applied to the conductors to be covered.

All line hoses should be cleaned and inspected regularly. A hand crank wringer can be used to spread the line hose to clean and inspect it for cuts or corona damage.

In-service care of insulating line hose and covers is specified in ANSI/ASTM D1050, Specification for Rubber Insulating Line Hoses.

6.6.0 Rubber Insulating Insulator Hoods

Pin type or post type of distribution primary insulators can be covered by hoods. The insulator hood properly installed will overlap the line hose, providing the lineman with complete shielding from the energized conductors.

Insulator hoods, like all other rubber insulating protective equipment, must be treated with care, kept clean, and inspected at regular intervals. Use canvas bags of the proper size attached to a handline to raise and lower the protective equipment when installing or removing it. See Figure 27.

Figure 27 – Rubber insulating insulator hood.

6.7.0 Conductor Covers

A conductor cover, fabricated from high dielectric polyethylene, clips on and covers conductors up to 2 inches in diameter. A positive air gap is maintained by a swinging latch that can be loosened only by a one quarter turn with a clamp stick.

6.8.0 Insulator Covers

Insulator covers are fabricated from high dielectric polyethylene and designed to be used in conjunction with two conductor covers. The insulator cover fits over the insulator and locks with a conductor cover on each end. A polypropylene rope swings under the crossarm and hooks with a clamp stick, thus preventing the insulator cover from being moved upward by bumping or wind gusts.

6.9.0 Crossarm Covers

High dielectric strength polyethylene crossarm covers are used to prevent tie wires from contacting the crossarm when the electrician ties or unties conductors adjacent to insulators. It is designed for single- or double-arm construction with slots provided for the double-arm bolts. Flanges above the slots shield the ends of the double-arm bolts. See Figure  28.

Figure 28 – Crossarm Cover.

6.10.0 Pole Covers

Polyethylene constructed pole covers are designed to insulate the pole in the area adjacent to high-voltage conductors. Pole covers are available in various lengths. Positive-hold polypropylene rope handles are knotted through holes in the overlap area of the cover. See Figures 7-29 and -30.

 

Figure 29 – Pole Cover.

Figure 30 – Poletop Cover.

6.11.0 Rubber Insulating Blankets

Rubber blankets (see Figure 31) cover odd-shaped objects (neutral clevis, transformer bushings, etc.). The blankets are secured with large “clothespins,” and available with or without a slot.

Figure 31 – Slotted Blanket.

Inspect blankets before each use by laying them flat and rolling them to stretch and expose any cuts or holes. Roll the blanket twice on each side, with the second roll 90 degrees from the first. As with rubber gloves, any cuts or abrasions deeper than one-quarter of the thickness of the rubber are unacceptable. Test blankets upon receipt and every 12 months thereafter.

Store blankets clean and dry flat on a shelf, hung from storage hooks, or rolled in a protective canister. If blankets are rolled for storage, do not tape them. Tape adhesive will chemically deteriorate the rubber. Do not store rolled blankets in a metal canister. Rust from a metal canister will degrade the blanket’s ability to protect you.

ANSI/ASTM D1048, Standard Specification for Rubber Insulating Blankets specifies in-service care of insulating blankets.

6.12.0 Safety Hat

Linemen, cablemen, and groundmen wear hard hats, or safety hats, to protect them against an impact from falling or moving objects and against accidental electrical contact of the head with energized equipment. In addition, hard hats protect the worker from sunrays, cold, rain, sleet, and snow. The first combined impact-resisting and electrical insulating hat was introduced in 1952. The hat was designed “to roll with the punch” by distributing the force of a blow over the entire head. This feature is accomplished by a suspension band which holds the hat about an inch away from the head and lets the hat work as a shock absorber.

The hard hat is made of fiberglass, or plastic material, and has an insulating value of approximately 20,000 volts. New helmets are manufactured to withstand a test of 30,000 volts without failure. The actual voltage that the hat will sustain while being worn depends upon the cleanliness of the hat, weather conditions, the type of electrode contacted, and other variables. The wearing of safety hats by linemen and cablemen has greatly reduced electrical contacts.

Physical injuries to the head have been practically eliminated as a result of workers on the ground wearing protective helmets. The Occupational Safety and Health Act of 1970 and most companies' safety rules require linemen, cablemen, and groundmen to wear safety hats while performing physical work. Specifications for safety hats are found in ANSI Standard Z89.1, Personal Protection - Protective Headwear for Industrial Workers.

6.13.0 Inspect and Maintain Hot Line Tools

De-energizing lines is not always possible or practical, so you need to have a way to safely handle energized conductors and equipment. Hot-line tools are used in these circumstances. Knowing proper operation and maintenance of these tools and equipment are vital to job completion on energized lines. In this section, you will learn the types of hot line tools and their purposes, inspections and tests performed on them, and how to maintain these items.

6.13.1 Purpose of Hot Line Tools

Hot line tools allow workers to do electrical work on energized lines and system components, without the fear of electrocution. See Figure 32.

Figure 32 – Hot line tools.

6.13.2 Hot Line Tools

There are many types of hot line tools, also called “hot-sticks.” They are constructed of fiberglass with aluminum “heads” in different configurations. These are a few of the more commonly used sticks.

Switch Stick. This hot line tool is used to safely open and close disconnect switches and fuse cutouts. Switch sticks are available in lengths from 2 to 20 feet. See Figure 33.

Figure 33 – Switch stick.

Grip All (Shotgun). The grip all stick, as seen in Figure 34, is commonly referred to as a “shotgun”. It’s primarily use is to install and remove ground sets and hot line clamps, although its design and versatility enables its use in a variety of other applications. Grip-alls are available from 4 to 12 feet in length.

Figure 34 – Grip all (shotgun).

Universal. The universal stick, as seen in Figure 35, has a head designed to mount a wide variety of tools or equipment items adapted for use with this stick. Items ranging from screwdrivers to socket wrenches to voltmeters can be attached to it.

Figure 35 – Universal stick with switch stick attachment.

Others (Tie Sticks & Wire Cutters). As stated, there are many different kinds of hot sticks; a few more are worth mentioning. Tie sticks (shown in Figure 36) are used to tie and untie conductor ties on energized lines. The heads of the sticks can be fixed or rotating blades or prongs.

Figure 36 – Tie sticks – rotary blade and rotary prong.

Wire cutters (seen in Figure 37) are used to cut energized conductors, jumper wire, or tie wire.

Figure 37 – Wire cutter.

There are also telescoping sticks called “extendo” sticks. See Figure 38. These range in size from six feet long when fully extended to 35 feet long. Most extendo sticks are equipped with universal heads.

Figure 38 – Extendo stick.

6.13.3 Maintenance of Hot-line tools

Since you use these sticks on energized high voltage lines, maintaining them is critical to your safety.

6.13.3.1 Inspections

Maintaining hot-sticks begins with inspections. Hot stick maintenance is the responsibility of everyone in the electrical shop, from the user to the supervisor.

As a user, you will be the one using these tools and are therefore best suited to identifying problems. Inspect hot stick tools prior to each use. Look for:

As a supervisor, it is mandatory that you perform an inspection of all hot line tools every six months. Supervisors maintain records showing the inspection date, dates of moisture and electrical tests, and date the next 6-month inspection is due. The purpose of this inspection is to ensure that the users of the sticks are performing their inspections, but do not depend upon the supervisor’s inspection to keep you safe.

Always inspect each hot stick before you use it.

6.13.3.2 Hot Stick Tester

Inspecting hot line tools is a good way to identify problems you can see. To identify problems you cannot see, you must rely on dielectric testing. Like inspections, perform testing of hot-line tools every six months.

The purpose of the hot stick tester is to determine the dielectric strength of hot sticks. It operates on the same principles as the High Potential DC test set, only in a much more user-friendly way.

The hot stick tester (as seen in Figure 39) is a portable way to test the dielectric strength of hot sticks. By simply placing the tester onto a stick, you bring two leads into contact with the fiberglass surface. One lead applies 1800 volts, and the other lead measures the amount of current that leaks between the leads. This leakage current appears on a meter mounted to the tester. The meter face is divided into two halves; one half marked “passes test” and the other half marked “dry out & retest.” By simply plugging the meter into an outlet and placing it on the stick, you will get an instant reading of good or bad.

Figure 39 – Hot stick tester.

Like any meter that tests resistance, the hot stick tester has to be calibrated or “zeroed” before use. Do this by turning the ZERO knob counterclockwise, then plug in the tester and switch it on. Turn the ZERO knob until the meter needle aligns with the ZERO line on the meter face. (See Figure 40).

Figure 40 – Meter Face.

When the meter is zeroed, you can test it for proper operation. Do this by using the “check stick” that comes with the meter. The check stick is a piece of hot stick that is intentionally faulted. Placing the meter on the check stick should cause the meter needle to fully deflect to the “dry out & retest” section. If the meter properly reads the check stick as bad, it is functioning properly and you are ready to test your sticks.

To begin testing, place the tester on one end of the hot stick. Take overlapping readings from one end to the other, testing the entire stick. Never slide the tester along the hot stick, always lift it clear before repositioning to avoid scratching the finish on the stick.

Rotate the stick 90 degrees and test again. Repeat the process to test all four quadrants of the stick. The total number of test segments performed on each stick will vary; just be sure to test each stick for its entire length in overlapping sections on all four quadrants. When complete testing on all four quadrants, repeat the entire procedure with the stick wet.

For the wet test, position the stick horizontally and spray it with distilled water. Use only distilled water, as it has no impurities and will leave no conductive residue on the stick. Tap water and bottled water have minerals that will leave residue when they evaporate. The objective is for the water to bead up on the glossy surface. Avoid over wetting, as this makes the beads of water form a continuous, conductive line. When the stick is properly wetted, use the same procedures as for the dry test. All readings should be in the green "passes test" range.

Prior to testing ensure the stick is clean, waxed, and inspected for nicks or abrasions.

Sticks with operating rods (such as shotguns and wire cutters) must be disassembled and the components tested separately.

If the stick fails any test, clean, wax, and test it again. If it fails a second time it probably has internal damage and must be returned to the manufacturer for reconditioning.

6.13.3.3 Care and Maintenance

Keep hot sticks kept clean and waxed, with a glassy appearance. When using hot sticks, never allow them to come into contact with the ground. When on the jobsite, keep hot sticks in the hot line trailer, on a portable rack, or on a clean tarp spread for the purpose. Always use the right stick for the job, and never use a damaged stick. Store sticks in a dry location designed specifically for the purpose. Hot line trailers are ideal places to store hot line tools; they are equipped with rubber coated hooks and tie downs to support and secure the sticks. Never store a stick dirty or wet. Wipe down each stick before storing.

 

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7.0.0 INSTALLATION of OVERHEAD DISTRIBUTION EQUIPMENT

In the construction and maintenance of  power distributions systems, you should be aware of the overhead distribution pole locations and the types of overhead distribution equipment used. An excellent source of information on distribution systems is The Lineman’s and Cableman’s Handbook.

Many different types and makes of overhead distribution equipment are in use today. This section will cover some of the standard equipment you will install and maintain, such as poles, transformers, capacitors, and interrupting and protective devices.

7.1.0 Pole Setting and Component Installation

7.1.1 Pole Locations

Your decision on the location of poles is limited because you will be either replacing existing poles or installing additional poles according to NAVFAC drawings and specifications. You may be asked to submit information (fact-gathering package) on a new power distribution addition to the base. If so, you need to consider the following recommended actions:

7.1.2 Poles

Utility poles that support electrical lines must be designed to support the conductors, insulators, and shield conductors in a manner that provides adequate electrical clearances. You must maintain a safe clearance when the conductor temperature is elevated as a result of a large amount of current flowing in a circuit and also when the conductors are ice coated or strong winds are blowing.

The three most common types of poles you will be working with are wood, reinforced concrete, and steel. See Figures 7-.41, 7-42, and 7-43. Other types of poles in use are aluminum, fiber glass, and polysil. As a certified lineman, you may be responsible for ordering, installing, and maintaining utility poles.

Figure 41 – Wood pole.

Figure 42 – Concrete.

Figure 42 – Steel.

Power lines supported by wood-pole structures are generally the most economical. In the United States, the southern yellow pine, western red cedar, and Douglas fir are the most commonly used species of tree for pole wood. All wooden poles are given a preservative treatment (normally pressure treated) to resist damage from insects and rotting. The service life of the utility pole can be doubled by preservative treatment. Many of the older poles now in use were treated with creosote.

 

Warning

Creosote is a toxic compound that irritates the skin and sometimes causes blistering. It is also carcinogenic and is being phased out because of groundwater contamination problems. Do not burn used creosote contaminated poles. They must be disposed of in Environment Protection Agency (EPA) approved landfills. Use extra care when working around poles treated with creosote. Avoid prolonged skin contact and wash thoroughly after handling. Launder clothing contaminated with creosote separately from family clothing.

Creosote oil, pentachlorophenol, and chromated copper arsenates have been used for preservation treatment of wood poles. Newer poles are treated with less toxic chemicals and, therefore, are safer to work with and also easier to climb (because the treatment softens the wood). They are environmentally acceptable because they do not contain materials that are toxic to mammals.

Wooden utility poles are classified by the length, circumference at the top of the pole, and the circumference measured 6 feet from the bottom of the pole. Pole sizes begin at 20 feet and are increased in 5-foot increments up to 100 feet in length. The pole top circumference increases 2 inches for every class of pole. There are 10 classes of wooden poles numbered from 1 to 10. Class 1 is the smallest, class 10 the biggest. The ANSI’s publication Specifications and Dimensions for Wood Poles (ANSI 05.1) provides technical data for wood utility poles.

7.2.0 Anchors

7.2.1 Purpose of Anchors

The anchor is the foundation of the pole line, and its purpose is to take the strain of all the weight of the equipment installed on a pole line. For example, on a straight pole line the strain of equipment, hardware and conductor support devices is distributed evenly along all the poles through the conductors. At the end of a pole line, or wherever the pole line changes direction, the strain is borne by only one pole. If left unsupported, this one pole will slowly be pulled toward the rest of the pole line until it collapses. To prevent this, a guy wire and anchor are installed. The guy wire transfers the strain from the pole to an anchor that is firmly imbedded in the earth.

Anchors are designed to meet specific soil conditions. You must know the type of soil before you can select a certain type of anchor. Anchors come in many forms and have different methods of installation.

7.2.2 Anchor Selection Criteria

You must consider three things when deciding what type of anchor to use: the type of soil in which the anchor will be installed, the holding capacity requirements, and the type of installation equipment available.

7.2.2.1 Subsurface Soil Conditions

Most soils can be divided into three general types, hard soil, ordinary soil, and soft soil. The hard soils include everything from solid bedrock to compact clay gravel mixtures. The ordinary soils include gravels, medium firm clay, loose sand/gravel mixtures and compact coarse sand. The soft soils include soft clay, compact fine sand, fill, and marshy soils.

The holding power of an anchor depends on the soil, so the anchor must be designed to hold well in the soil into which it is installed. Be very careful when determining soil type, because an anchor that holds very well in ordinary soil will not hold at all in soft soil, and a soft soil anchor cannot be installed in hard soil without damaging the anchor. Remember that if the soil does not hold the anchor, the anchor will not support your pole line.

7.2.2.2 Holding Requirements

Holding capacity is the amount of pull, in pounds, the anchor must withstand. Since strain is transferred from pole to pole through the conductors, at a minimum, an anchor must be able to withstand tension equal to the combined breaking strength of the conductors.

As an example, suppose you need to install an anchor for a pole that terminates four 1/0 Aluminum Conductor Steel Reinforced (ACSR) conductors (conductors will be discussed in greater detail later in this block). According to wire specification charts, each conductor of this type and size has a breaking strength of 4,280 pounds. Since there are four of them the total breaking strength is 17,120 pounds. Your anchor installation must be able to withstand a minimum of 17,120 pounds of tension.

7.2.2.3 Installation Equipment

When selecting an anchor, always take into consideration the type of equipment available to you. It would be foolish to install an anchor by hand if a line truck could do it in less time with considerably less effort. Conversely, there may be times when the line truck cannot get to where the anchor will be installed. The type of equipment required will be determined by both the installation location and the type of anchor to be installed. Hand tools such as shovels, digging spoons and digging bars could be required.

7.2.3 Types of Anchors

The term anchor is used as a collective term, but the anchor actually consists of the anchor rod and the anchor assembly. This section addresses three varieties of anchors.

These three types of anchors are manufactured and are commonly used because of their ease of installation.

Another type of anchor, called a deadman, is not manufactured. This anchor is made of a 6 to 8 foot long piece of treated power pole and an anchor rod. It is installed 6 feet deep in loose or sandy type of soil, with an angle of pull for the guy wire and rod assembly equal to 45 degrees. The deadman anchor is not widely used today because of the time and effort required to place it.

Rock Anchor- The rock anchor is installed in the hardest soil of all: solid rock. It is designed to fit into a hole drilled into the rock (called a pilot hole), then opened by turning the anchor rod. As you can see from Figure 44, when the anchor is opened it will expand against the sides of hole. This wedging action holds the anchor in place.

Figure 44 – Rock anchor.

Expansion Anchors- The expansion anchor is the most popular type and is designed to be placed in the ground and then expanded with the aid of the tamping bar. Once expanded, the anchor is secure and strong enough to secure the guy. Expansion anchors are commonly used in ordinary soils. Like a rock anchor, the expansion anchor requires a pilot hole. Unlike the rock anchor, an expansion anchor does not hold by wedging itself against the sides of the hole; instead, the anchor is expanded into the undisturbed soil surrounding the pilot hole. This process will be explained later, in the discussion of installation procedures. Figure 45 shows an expansion anchor before expansion has taken place.

Figure  45 – Expansion anchor.

Screw Anchor- Screw anchors (as seen in Figure 46) are commonly installed in soft soils. Unlike the rock and expansion anchors, the screw anchor does not require a pilot hole. The anchor is simply screwed into the ground, where it holds itself in place. If the soil is soft enough, two people can do this by sliding a digging bar through the eye of the anchor rod and walking in a circle to screw the anchor in. If a line truck is available to aid in the installation, the screw anchor can also be used in ordinary soil with excellent results.

Figure 46 – Screw anchor.

7.2.4 Equipment and Tool Requirements

7.2.4.1 Rock Anchor

Since rock anchors need a pilot hole, you will need tools, such as a jackhammer, a hammer, or a chisel and hammer, to make a hole in solid rock. You will also need a digging bar to turn the anchor rod to open the anchor.

7.2.4.2 Expansion Anchor

Since the expansion anchor requires a pilot hole in the soil, you will need digging tools or the auger from the line truck. Once the anchor is in place, expand it with a special tool called an anchor buster. This is like a large slide hammer, which is fitted around the anchor rod and then used to pound on the top of the expansion anchor, flattening and expanding it. You will also need shovels and tampers to backfill and tamp the pilot hole.

7.2.4.3 Screw Anchor

The screw anchor does not need a pilot hole, so you do not need digging tools. If you are installing the screw anchor manually, use a digging bar to thread through the eye of the anchor rod for turning it. If you are using the line truck, fit an adapter to the Kelly bar of the line truck and use the auger motor to screw the anchor into the ground.

7.2.5 Installation Procedures

To install an anchor, you need to know two things: how far from the pole the to place the anchor, and at what angle to install the anchor. You can find both these items of information on the staking sheet or the specification sheet for the individual pole. The distance from the pole to the anchor is called the “lead”, and should be listed in feet. The angle will be listed in degrees, and will most likely be 45?. This is the preferred angle for most guy wires, and you always install the anchor at the same angle as the guy.

Whether digging a pilot hole or simply screwing the anchor into the ground, bear in mind that when you apply tension to the anchor, the eye of the anchor rod should be 6 inches above grade.

7.2.5.1 Rock Anchor

To install a rock anchor, first make a pilot hole. The easiest method is to have the equipment shop jackhammer the hole for you, but you can do it yourself with a hammer drill or a hammer and chisel, if necessary. Once the pilot hole is made, slide the closed anchor into the hole, and then open the anchor by turning the anchor rod.

The easiest way to do this is by sliding a digging bar through the eye of the anchor rod and walking in a circle. When you are finished, fill in the pilot hole with a bag of ready- mix concrete to keep it from filling with water and debris.

7.2.5.2 Expansion Anchor

Like a rock anchor, the expansion anchor also requires a pilot hole. Dig the hole deep enough so the anchor rod eye will be 6 inches above grade when tension has been applied. Remember to dig the hole at the same angle as the guy wire.

Then insert the expansion anchor and anchor rod into the hole, fit an anchor buster to the anchor rod (if an anchor buster is unavailable, a ten-foot piece of heavy 2 inch conduit or pipe will work), and work the anchor buster up and down to expand the anchor. As the anchor buster pounds on the top of the anchor, the anchor flattens out and penetrates the undisturbed soil around the pilot hole. This undisturbed soil holds the expansion anchor in place.

When the anchor is completely flattened and expanded, backfill and tamps the pilot hole all the way to the top.

7.2.5.3 Screw Anchor

Screw anchor installation is very simple. To install a screw anchor manually, you must install it in soft soil. Simply slide a digging bar through the eye of the anchor rod and have two people walk in a circle, being careful to maintain the required angle.

In ordinary soil, manual installation is difficult or impossible, so you must use the line truck. Begin by removing the auger from the Kelly bar, then attaching the adapter to the end of the Kelly bar. Attach the adapter to the screw anchor, and simply use the auger motor to screw the anchor into the ground. Remember to keep the proper angle, and turn the anchor in until the eye of the anchor rod is six inches above grade.

7.2.6 Anchor Rods

The anchor rod serves as the connecting link between the anchor and the guy cable. The rod must have an ultimate strength equal to, or greater than, that required by the down guy assembly. Anchor rods vary in diameter from 1/2 to 1 1/4 inches and in length from 3 1/2 to 12 feet.

7.2.7 Safety

Anchor installation is a fairly safe operation, although you must take care around equipment such as the line truck and jackhammers. When chipping away rock, wear eye protection.

7.3.0 Pole Guys

When constructing power lines, you will need a means of strengthening poles and keeping them in position. To accomplish this, you can use guys, anchors, and braces. Anchors are buried in the ground, and guy wires are connected to the anchors and attached to the pole, or you can use a push brace. The guys and braces counter the horizontal strain on the pole caused by conductors, pole-line components, and abnormal loads, such as snow, sleet, or wind. See Figure 47.

Figure 47 – Guy was needed here.

7.3.1 Purpose of Guying Poles

A guy is a brace or cable fastened to the pole to strengthen it and keep it in position. Use guys whenever the wires tend to pull the pole out of its normal position and to sustain the line during the abnormal loads caused by sleet, wind, and cold. Guys counteract the unbalanced force that dead-ending conductors impose on the poles; by changing conductor size, types, and tensions; by changes in angles in the transmission or distribution line, and by changes in pole line elevation. The guy counteracts the horizontal component of the force while the pole or supporting structure acts as a strut resisting the vertical component of the forces.

7.3.2 Types of Guys

7.3.2.1 Down Guy

A "down guy" consists of a wire running from an attachment near the top of the pole to a rod and anchor installed in the ground (Figure 48). This type of guy is preferable if field conditions permit its installation since it transfers the unbalanced force on a pole or structure to the earth without intermediate supports.

Figure 48 – Down guy.

A down guy used at the ends of pole lines to counterbalance the pull of the line conductors is called a "terminal guy" or a "dead end guy" (Figure 49). All corners in the line are considered dead ends. They should be guyed the same as terminal poles, except that there will be two guys, one for the pull of the conductor in each direction (Figure 50).

Figure 49 – Dead-end guy.


Figure 50 – Corner guy.

7.3.2.2 Side Guy

When the line makes an angle, it produces a side pull on the pole. Install side guys to balance the side pull (Figure 51). When a branch line takes off from the main line, it produces an unbalanced side pull. Place a side guy on the pole directly opposite to the pull of the branch line

Figure 51 – Side guy.

7.3.2.3 Storm Guy

Guys are installed at regular intervals in transmission lines that extend long distances in one direction to protect the lines from excessive damage from broken conductors. Guys installed to protect the facilities and limit the damage if a conductor breaks are called "line guys" or "storm guys" (Figure 52).

Figure 52 – Storm guy or line guy.

7.3.2.4 Sidewalk Guy

A “sidewalk guy” is an anchor guy with a horizontal strut at a height above a sidewalk sufficient to clear pedestrians (Figure 53).

Figure 53 – Sidewalk guy.

7.3.2.5 Span Guy

A span, or overhead, guy consists of a guy wire installed from the top of a pole to the top of an adjacent pole to remove the strain from the line conductors. The span, or overhead, guy transfers the strain on a pole to another structure. This may be to another line pole or to a stub pole on which there is no energizer equipment. A span guy is always installed to extend from the strain pole to the same or lower level on the next line pole.

7.3.2.6 Head Guy

A guy wire running from the top of a pole to a point below the top of the adjacent pole is called a "head guy" (Figure 54). Lines on steep hills are normally constructed with head guys to counteract the downhill strain of the line.

Figure 54 – Head guy.

7.3.2.7 Arm Guy

A guy wire running from one side of a crossarm to the next pole is called an "arm guy." Arm guys counteract the forces on crossarms that have more wires dead-ended on one side than on the other (Figure 55).

Figure 55 – Arm guy.

7.3.2.8 Stub Guy

A guy wire installed between a line pole and a stub pole on which there is no energized equipment is called a "stub guy" (Figure 56). A down guy is used to secure the stub pole. This type of guy is often installed to obtain adequate clearance for guy wires extending across streets or highways.

Figure 56 – Stub guy.

7.3.2.9 Push Guy

A push guy, or a push brace, is used when it is impossible to use down guys (Figure 57). When it is impossible to obtain sufficient right-of-way for a pole guy, the push brace can usually be installed. The push guy is constructed from an old power pole and a special bracket called a push brace attachment.

Figure 57 – Push guy.

7.3.3 Attachment Devices

The guy wire must be attached both to the utility pole and to the anchor rod. There are three methods of attachment.

7.3.3.1 Three-bolt Clamp

A three-bolt clamp (Figure 58) is so named because it has three bolts designed to clamp two grooved pieces of steel together on a guy wire. It has two outer bolts facing one way and a center bolt facing the other way. When tightening, evenly torque the three bolts to grip the wire uniformly. These clamps are easy to remove and re-apply.

Figure 58 – Three-bolt clamp.

7.3.3.2 Preform Guy Wire Grip

A preform guy wire grip (aka preform wrap) is a quick method of attachment that requires no tools to apply or remove. You simply wrap the preformed wrap onto the wire, and when you apply tension, the wrap holds the wire much like the toy finger handcuffs you played with as a child. The more tension applied to the wrap, the tighter the wrap holds the wire. Once tension has been applied to a preform wrap, it can still be removed, but it cannot be reused. Figure 59 shows a preform wrap before installation and a preform wrap being applied to a guy wire.

Figure 59 – Preform guy wire grip

7.3.3.3 Automatic Locking Clevis

Automatic locking clevis (aka automatics) guy wire attachments are devices with spring-loaded jaws inside the body of the device. The guy wire can be inserted into the jaws, but cannot be removed unless the spring pressure is released with a screwdriver. Automatics install very quickly; however, they cannot be reused once tension has been applied. Figure 60 shows an automatic guy attachment. The cartridge at the bottom of the Figure 60 is shown in a cutaway view in Figure 61.

Figure 60 – Automatic locking clevis.

Figure 61 – Cutaway of automatic.

7.3.4 Associated Hardware

7.3.4.1 Rods

The guy wire is attached to the “eye” of the anchor rod. Rods are available with an oval eye or a thimble eye, each of which allows only one guy wire to be attached to the anchor rod. Twin eyes allow two guy wires to be attached to one anchor rod, while a triple eye will hold three guy wires. Triple eyed anchor rods are normally the best choice for most installations as they allow for future growth on the pole. Figure 62 shows an oval eye, a twin eye and a triple eye. You can purchase anchor rods in various lengths and diameters, according to need.

Figure 62 – Anchor rod oval, twin and triple eyes.

7.3.4.2 Pole Hardware

Guy wires are attached to the utility pole with a thimble eyebolt, a thimble eye nut or a thimble eye washer.

Thimble eyebolts are standard 5/8 inch bolts forged with a thimble as the head of the bolt. Thimble eyebolts come straight or with the thimble bent at a 45 degree angle. Use the straight variety for span guys and head guys; use the bent thimble eyebolts for down guys and sidewalk guys.

Thimble eye nuts are used just like standard nuts, except each one comes with a straight thimble eye forged onto it. Because the thimble is straight, thimble eye nuts are used for span guys and head guys; if you need a bent thimble, you must use a thimble eye washer. Thimble eye washers are stout washers forged with a thimble eye at a 45 degree angle for use with down guys and sidewalk guys. Install the thimble eye washer under a nut, making sure you tighten the nut down snugly. When using a thimble eye nut, spin the nut on the bolt until at least two full threads of the bolt are visible.

Never use a bent thimble for a span guy or a head guy, and never use a straight thimble with a down guy or sidewalk guy. Eyebolts and eye nuts can be purchased with oval eyes suitable for mounting insulators and other line hardware, but never use an oval eye to attach a guy wire. The sharp bend around the oval places undue stress on the wire. Always use a thimble eye for attaching guy wire. Figure 63 shows the different thimble eyebolts.

Figure 63 – Bent thimble eyebolt, straight thimble eyebolt, thimble eye washer and thimble eye nut.

7.3.5 Equipment and Tool Requirements

To properly tension a guy wire, some equipment is required.

7.3.5.1 Guy Wire Grip

A guy wire grip (Figure 64) is a tool used to hold the guy wire as tension is applied. It is designed so that when clipped onto the guy wire, applying tension causes the jaws to close tighter. The jaws are equipped with small teeth to bite into and hold the steel guy wire.

Figure 64 – Guy wire grip.

7.3.5.2 Dynamometer

A dynamometer (Figure 65) is a device that measures tension in foot pounds. When using a dynamometer, you will also need a reference chart that gives you the proper amount of tension to apply.

Figure 65 – Dynamometer.

7.3.5.3 Anchor Grip

If you need a way to attach to the anchor rod, use an anchor grip (Figure 66). The anchor grip is a two-piece steel tool that bolts onto an exposed anchor rod, providing an eye for attaching a chain hoist.

Figure 66 – Anchor grip on thimble eye rod.

7.3.5.4 Chain Hoist

A chain hoist (sometimes called a “come-along”) is used to apply tension to the guy wire (Figure 67). Chain hoists are available with different capacities; be sure to use one strong enough to apply the required tension to your guy wire.

Figure 67 – Chain hoist.

7.3.6 Installation Procedures

The following procedures are for installing a down guy. Procedures to install other types of guys will vary slightly. See Figure 68.

Figure 68 – Guy wire installation hardware.

7.3.6.1 Attach One End of Guy Wire to Pole

Attach the guy wire at the top of the pole at a point determined by the staking sheet or specification sheet. Mount a bent thimble eyebolt or a thimble eye washer on the pole and secure the guy wire to it with one of the three guy attachment devices discussed earlier.

 

Note

It is often easier to attach the guy wire to the thimble eyebolt or thimble eyewasher while on the ground, then carry the assembly up the pole and mount it.

7.3.6.2 Attach Other End of Guy Wire to Anchor Rod

The procedure to attach the guy wire to the anchor rod will vary depending on which guy attachment device you use.

Three-bolt Clamp. To attach the guy wire to the anchor rod using a three-bolt clamp, first thread the guy wire through the eye of the anchor rod. Pull the “tail” of the guy wire (the tail is the end of the guy wire now sticking out of the anchor rod eye) tight. Hang a guy wire grip on the guy wire “downrunner” (the downrunner is the section of guy wire that runs from the pole to the anchor rod eye). Hang the chain hoist on the guy wire grip.

Note

Hang the guy wire grip on the downrunner at head-level. Doing so will put the chain hoist in the most advantageous operating position.

After attaching the chain hoist, attach a second guy wire grip to the tail of the guy wire. Attach the chain of the chain hoist to the second guy wire grip. Operate the chain hoist handle to draw the tail and downrunner together, tensioning the guy wire.

If you are using a dynamometer and chart to set the proper tension on the guy wire, install the dynamometer between the chain hoist and either of the guy wire grips. Operate the chain hoist until the dynamometer indicates the amount of tension indicated on the chart. If no dynamometer is available, you will “rake” the pole. Raking the pole is applying tension to the guy wire until the top of the pole is pulled toward the anchor rod. Rake the pole two inches for each ten feet of pole height above ground. For example, if there is 30 feet of exposed pole, rake the top of the pole 6 inches toward the anchor rod.

Once you have achieved the proper amount of tension, secure both the tail and the downrunner in the grooves of the three-bolt clamp and tighten the three bolts. Trim the excess guy wire tail and remove the chain hoist, guy wire grips, and dynamometer (if used).

Preform Guy Wire Grip. To attach the guy wire to the anchor rod using a preform wrap, first hang a guy wire grip on the downrunner, then hang the chain hoist on the guy wire grip. Attach an anchor grip to the anchor rod, and attach the chain of the chain hoist to the anchor grip. If using a dynamometer, install it between the chain hoist and either of the two grips. Operate the handle of the chain hoist to tension the guy wire.

When the guy is properly tensioned, thread the preform wrap through the eye of the anchor rod. Wrap first one side and then the other of the preform wrap onto the downrunner. Trim any excess guy wire from the lower end of the preform wrap and remove your equipment.

Automatic Locking Clevis. To attach the guy wire to the anchor rod using an automatic, hang a guy wire grip on the downrunner, then hang the chain hoist on the guy wire grip. Attach an anchor grip to the anchor rod, and attach the chain of the chain hoist to the anchor grip. If you are using a dynamometer, install it between the chain hoist and either of the two grips. Operate the handle of the chain hoist to tension the guy wire.

When the guy is properly tensioned, attach the automatic to the anchor rod. Firmly thread the end of the guy wire through the cartridge of the automatic until all slack is removed. Remove the tensioning equipment. Trim the excess guy wire emerging from the back of the automatic cartridge, leaving two inches of wire exposed.

Regardless of the method used to attach the guy wire to the anchor rod, the final step of guy installation is attaching a guy guard to the guy wire. Guy guards are used to bring attention to the presence of the guy so that drivers and pedestrians can more easily avoid them. Most guy guards are brightly colored to attract attention; however, on some military installations they are a subdued color to fit more easily into the base color scheme.

7.3.7 Safety

Take great care when cutting a guy wire. The steel will whip out when cut and the severed end will be very sharp. Firmly hold both sides of the wire being cut.

7.4.0 Framing Poles

Framing a pole consists of the following actions: determining the face and back of the pole, cutting the roof and gain, and drilling holes for mounting hardware.

Figure 69 shows that the face of any pole is on the inside of any curve the pole may have. This allows the wire strain on the crossarm to be against the curve of the pole. This also dictates positioning of the gain on the face of the pole, except for gains on comer poles, when lower crossarms are mounted at a 90 degree angle to the main distribution line.

Figure 69 – Parts of a pole.

The roof or top of the pole is cut sloping at a 15 degree angle from the face to the back of the pole; however, the new pressure-treated poles do not require roofs.

A gain should be 1/2 inch deep in the center, slightly concave, and located 12 inches from the top of the pole. The width of the gain should be the height of the crossarm to be used. Spacing of succeeding gains depends on the voltage of the lines to be placed on that level. This information is contained in the project specifications and drawings for any new work for which you are tasked.

To drill holes for mounting crossarms, use a template that can mark the center, or draw two diagonal pencil lines across the gain. The intersection of these two lines determines the center of the gain and the place to drill the hole. The nominal size hole is 1 1/16 inch for a 5/8 inch through bolt.

7.5.0 Installing Poles

The depth for a pole hole depends on the length of the pole and the composition of the soil. A hole in firm, rocky terrain does not need to be as deep as a hole in soft soil. Table 2 gives recommended depths for poles from 20 to 60 feet long in firm soil and in rock.

Table 2 – Depth for setting poles in soil or rock.

Length of Pole
(ft)
Setting Depth
(ft)
In Soil In Rock
20 5.0 3.0
25 5.5 3.5
30 5.5 4.0
35 6.0 4.0
40 6.0 4.0
45 6.5 4.5
50 7.0 4.5
55 7.5 5.0
60 8.0 5.0

A pole set in sandy or swampy soil must be supported by guys, braces, or cribbing. Cribbing means placing some firm material around the part of the pole below the ground. One method of cribbing is to sink an open-bottom barrel in the hole, set up the pole in the barrel, and then fill the space around the base of the pole with concrete or small stones after the pole has been plumbed (brought to the vertical). Another method of cribbing is shown in Figure 70.

Figure 70 – Cribbing a pole with stones and a log.

There may be a power-driven hole digger available, but in the absence of one of these, you must dig the holes with hand tools. Use a "digging bar" to loosen the soil. You can remove about the first 2 feet of depth with a short-handled shovel. Below that, loosen the earth with an earth auger or long-handled shovel, and haul it up with a long-handled device called a spoon. Hole depths vary from 3 to 8 feet depending if digging in soil or rock.

A hole should have a diameter about 6 inches larger than that of the base of the pole to allow room for tamping backfill. It should be a little larger at the bottom to allow for plumbing the pole.

7.6.0 Erecting Poles

When an earth auger is available, the job of erecting poles is relatively simple. Place a sling around the approximate midpoint of the pole and heave it up with a winch. Then a pole claw holds it in place.

The truck then proceeds to the hole or is pre-positioned at the hole site, and the base of the pole is guided in as the winch lowers away (Figure 71). Since the butt, or base, is heavier than the top end, raise the pole to an almost vertical position.

Figure 71 – Auger truck setting a pole.

In the absence of this equipment, the pole must be "piked up" meaning that the pole is placed with the base adjacent to the hole and the upper end supported on either a "mule" or a "jenny." A jenny is a wooden support made in the form of an X, and a mule is a wooden support made in the form of a Y. The upper end is then "piked" into the air by crew members using pike poles. A cant hook (peavy), pike pole, and pole support (mule) are shown in Figure 72. Figure 73 shows the tool used to position a pole manually for erection

Figure 72 – Pole positioning tools.


Figure 73 – Manual lifting tool.

The procedure for piking up a pole is shown in Figure 74. The "butt man" holds and guides the butt of the pole with a cant hook (or peavy) (Figure 72). This is a handle with a hook designed to grasp the pole when pressure is applied to the handle. As the upper end of the pole is raised, a crew member keeps the jenny or mule in approximate contact by moving it toward the butt. The "butt board" is a length of plank set in the hole and long enough to protrude above the surface. It prevents the butt of the pole from sliding past the hole and also prevents the butt from caving in the side of the hole. After the pole has reached an upright position, it is "faced", meaning it is rotated with the cant hook to bring the crossarm gain to proper position. On a straight line crew members set adjacent poles with crossarms facing in opposite directions, as shown in Figure 75. This procedure, called facing "gain to gain" or "back to back," provides for maximum strength in the line.

Figure 74 – Piking up a pole.


Figure 75 – Poles facing in a straight line.

Poles are always faced in the direction of hills, curves, and dead ends to allow the most strain to be placed on the face and against the curve of the poles.

After the pole has been faced, it must be plumbed vertical. To do this, four pikers on four sides of the pole act on signals given by one crew member who sights along the line and another who sights from one side. In some cases, a small amount of rake or lean (approximately 12 inches) is left to allow for a wire strain or the normal give of a guy.

Do not use the pike-pole method of setting poles unless there are enough crew members to do the work safely. In using pikes the crew must stand far enough apart so that they will not interfere with each other. Never brace a pike pole on your stomach. If the pole shifts your way, you will not be able to get clear. Never rely on unmanned pikes alone to support a pole, while a crew member is on it. Keep pike-pole tops covered at all times except when actually in use.

After the plumbing the pole, backfill the hole and the tamp the backfill down firmly. Backfill gradually, in shallow layers, and tamp down each layer thoroughly. Usually two or three crew members tamp, and one shovels. When the hole has been filled to the ground line with tamped backfill, bank the remaining excavated soil is banked in a mound around the base of the pole to allow for subsequent settling (Figure 76).

 

Warning

As a pole is being raised, it is safest to assume that at any moment something may slip or break Stand as far away from the pole as possible if you are not in the raising crew.

Figure 76 – Tamping and backfilling erected pole.

No crew members should be on poles, during plumbing, canting, or tamping.

7.7.0 Installing Guys

Guys are assembled using seven-strand galvanized steel guy wire, a strain insulator (of a different design from and not to be confused with the strain insulator used for dead ending a conductor), and three bolt clamps or preformed guy grips. The dimensioning of the guy is determined by the height of the pole, by the amount of strain it must counteract, and by the climate when the guy is installed.

7.8.0 Secondary Racks

Secondary conductors may be strung on crossarms but are usually put on secondary "racks." These racks are made in sizes to accommodate two, three, or four conductors.

A secondary rack is mounted on the side of a pole (for a straight run) or on the inside of a pole (for a dead end). A rack is fastened to the pole with lag bolts on a straight line with a through bolt at the top and a lag screw at the bottom, or with through bolts with nuts for a dead end or when a branch line takes off from the main line. Figure 77 shows a dead end secondary rack.

Figure 77 – Dead-end secondary rack.

On a straight line without excessive strains, crossarms are singly-mounted face to face or back to back. At line terminals, corners, angles, or other points of excessive strain, crossarms are doubled. When a power line crosses a railroad or a telephone line, crossarms is also doubled.

A rod passing through the insulators and brackets on a rack holds the insulators to the rack, as shown in Figure 77. On a straight line or inside angle, the conductor is run on the inside of the insulator. On an outside angle, it is run on the outside. Always place the conductor here with strain against the insulator. Figure 78 shows rack arrangements at comers and angles.

Figure 78 – Rack arrangements at corners and angles.

7.9.0 Crossarms

A crossarm is a specially treated wooden member secured to a pole and used to mount various types of circuit protection devices and support distribution conductors.

Standard cross-section dimensions for wood crossarms (width by height) are:

The length of the crossarm depends on the number of conductors it must support and the spacing between them. Typically, 4 and 6 conductor crossarms are 8 feet in length.

In your naval service you may come across larger wooden crossarms or crossarms made of steel. These crossarms are designed to support increased strain or to use with transmission lines carrying higher voltages.

7.9.1 Types of Crossarms

7.9.1.1 Single Arms

Single arms are used on straight lines when no excessive strain needs to be provided (Figure 79). When you install crossarms, face every other crossarm in the same direction. Use single crossarms when the pole line is straight or line angle change is less than 10 degrees.

Figure 79 – Single-arm construction.

7.9.1.2 Double Arms

Use a double arm at line terminals, corners, angles, or other points when there is an excessive strain (Figure 80). Also use double arms when lines cross telephone circuits or railroad crossings, as such points require more than ordinary safety. As a rule, double arms provide support when two or more transformers are mounted on the same pole.

Figure 80 – Double-arm construction.

Use two crossarms at points where the line angle change is from 11 to 30 degrees or when lines cross telephone circuits or railroad crossings, also use double arms, as more than ordinary safety is required at such points. When two or more transformers are mounted on the same pole, use double arms, as a rule, for their support. This configuration is called a double arm. Double crossarms utilize one through bolt and two double arming bolts. Double arming bolts, also called DA bolts, and are long bolts without heads that extend through both crossarms at the extreme ends of the arms.

7.9.1.3 Buck Arms

Buck arms are used at points where the line makes a change of between 31 to 90 degrees, or where the conductors deadend. Buck arms look like the double crossarm, except they use four double arming bolts in construction compared to just two on the double crossarm. These provide additional strength to the arm and an attachment point for the suspension insulators used with a buck arm configuration. You add a second set of buck arms in order to make a line angle change. When installing the second set of arms, install them 2 to 4 feet below the first set of arms, 3 feet being the most common spacing. Again, the exact spacing will depend on system voltage. (See Figure 81)

Figure 81 – Buck-arm construction.

7.9.1.4 Side Arms

Side arms are used in alleys or other locations when it is necessary to clear buildings. (See Figure 82).

Figure 82 – Side-arm construction.

7.9.2 Hardware

Line hardware consists of the miscellaneous bolts, nuts, braces, and clamps used to fasten crossarms, guys, and other equipment to the pole.

7.9.2.1 Crossarm Braces

Braces give strength and rigidity to the crossarm. Metal crossarm braces are made of either flat bar or light angle iron. The size of a brace varies with the size of the arm and the weight of the conductors. The usual flat-strap brace for ordinary distribution work (Figure 83) is 38 inches long and 1/4 by 1 1/4 inches. One end is attached to the crossarm by means of a carriage bolt and the other to the pole by means of a lag screw. One brace extends to each side of the arm.

Figure 83 – Standard flat-strap crossarm brace

Angle iron braces are made in one piece and bent into the shape of a V, as shown in Figure 84. These braces are fitted to the bottom of the crossarm instead of the side as is the flat type. Figure 85 gives an example of how these braces are used.

Figure 84 – A V shaped angle iron crossarm brace.


Figure 85 – Crossarm brace installation.

7.9.2.2 Common Hardware

Figure 86 shows some samples of common hardware used in power distribution.

Figure 86 – Line hardware.

7.9.3 Crossarm Installation

On most pole-line construction, hardware and crossarms are installed on the ground before setting the pole. This is the easiest and most efficient method; however, sometimes it is necessary to upgrade or build on to an existing system, and then the arm must be installed on a pole that is already standing.

7.9.3.1 Single Crossarm

When you mount the crossarm on the pole before the pole is set, tighten the through bolt, but leave the crossarm braces hanging loose. Once the pole is set, level the crossarm and secure the braces to the pole. Finally, draw the through bolt completely tight.

Do not raise the arm with the insulators installed; send them up last and spin them on after securing the arm. Remember that the grooves of pin insulators must line up with the conductors. To properly align a pin insulator, adjust the pin, not the insulator. Spin the insulator onto the pin until snug, but do not exert excessive force as the porcelain or plastic will break. When the insulator is snug, loosen the nut on the insulator pin (bottom of the crossarm) and turn the entire pin/insulator assembly to align the groove. Retighten the nut on the insulator pin when you are satisfied with the alignment.

To mount the crossarm after the pole is set, a worker on the ground pulls it up to a lineman in a working position.

Braces are usually fastened to a crossarm with 3/8-inch by 4-inch carriage bolts. Each brace comes down diagonally and is attached to the pole at the lower end with a 1/2 inch lag screw.

On a straight line without excessive strains, use crossarms singly-mounted face to face or back to back, as previously mentioned. At line terminals, corners, angles, or other points of excessive strain, double crossarms. When a power line crosses a railroad or a telephone line, you also need to double crossarms.

7.9.3.2 Double and Buck Crossarms

When installing double crossarms and buck arms, mount all the hardware on one crossarm and install it first; the number of DA bolts depends on whether it is a double arm or a buckarm. See Figure 87. One of the DA bolts is threaded all the way and has two square washers and two nuts on each bolt between the arms. The bolts should be set up loosely in order to allow free movement, making alignment of the second arm easy. When installing each crossarm, follow the same procedures as for the single arm.

Figure 87 – Crossarm Installation.

If you use pin insulators, follow the procedures described for the single crossarm. If you use suspension insulators, you will need to install an oval eye nut or an oval eyebolt on which to hang the insulator. Mount suspension insulators to the oval eye with a short clevis pin and cotter key. Be sure to install the cotter key(s) on the side of the insulator closest to the pole. This is much more convenient for a climber than having to fumble for a small cotter key on the opposite side of the insulator from the pole. (See Figure 88)

Figure 88 – Mounting a suspension insulator.

7.9.3.3 Clevis Assembly

Installing a clevis and spool insulator is relatively simple. Mount the through bolt/clevis assembly to the pole, and then secure the spool insulator in the clevis with a clevis pin and cotter key. Ensure the spool insulator is correctly oriented with the grooved end on top, and drop the clevis pin through the clevis/spool from above with the cotter key inserted on the bottom side. (See Figure 89)

Figure 89 – Proper orientation of spool insulator on a clevis.

7.10.0 Insulators

An insulator is a material that prevents the flow of an electric current and can be used to support electrical conductors. The function of an insulator is to separate the line conductors from the pole. Insulators are fabricated from porcelain, glass, and fiber glass, treated with epoxy resins and rubberlike compounds. In determining the size and type you need, you should consider the designed voltage of the circuit, conductor size, length of the pole-line spans, and cost of the various insulators. The most common types of insulators found in Navy use are the pin, post, suspension, and strain insulators.

7.10.1 Pin and Post Insulator

The pin insulator is the most commonly used insulator on overhead distribution systems today. It is screwed on a steel or lead insulator pin (thus the name) mounted to a crossarm or on some variation of armless hardware. Pin insulators have a groove across their tops, designed to hold the conductor. This groove must be positioned in-line with the conductor it is supporting. Pin insulators are used when the right-of-way is narrow. A post insulator is similar to a pin insulator but is used for longer, heavier spans. The post insulator is seen mostly on sub-transmission and transmission lines. It is not mounted on a pin; its base is bolted onto the crossarm.

Pin insulators are made of either glass or porcelain. The glass insulator is always one solid piece. The porcelain insulator is also a one-piece insulator when used with low- voltage lines but will consist of two, three, or four layers cemented together to form a rigid unit when used on higher voltages (Figure 90).

Figure 90 – Pin insulator.

An insulator pin holds the insulator mounted on it in a vertical position. Insulator pins are made of wood or metal. Wooden pins are usually made of locust, a durable wood that retains its strength longer than other woods. Iron and steel pins are used whenever the pins must be extra long because of high voltage and whenever the tension on the conductor is great. One make is arranged to encircle the crossarm as a clamp pin, the clamp being held by bolts. In many cases, a steel rod is used as the base to permit the drilling of a 5/8 or a 3/4 inch hole in the crossarm.

Steel pins are in general use. Steel pins have a broad base which rests squarely on the crossarm, as shown in Figure 91.

Figure 91 – Steel pin.

The spacing of the pins is generally suited to the voltage of the circuit. The spacing should provide sufficient working space for the lineman. For general distribution work, the spacing is 14 1/2 inches between centers.

7.10.2 Suspension Insulators

As their name implies, suspension insulators (as seen in Figure 92) are suspended from a crossarm, pole or armless hardware in either a horizontal or vertical position. The suspension insulator can be installed in series with other suspension insulators to accommodate higher line voltages. Older suspension insulators were made of porcelain but the insulators we use now are made of polymer or epoxy material (plastic).

Figure 92 – Suspension insulator.

7.10.3 Strain Insulator

The strain insulator looks exactly like the suspension insulator but is designed to hold much heavier physical loads. Strain insulators are used to carry a pull as well as provide insulation. Such places occur whenever a line is dead-ended, at comers, at sharp curves, at extra long spans, at river crossings, or in mountainous country. In such places the insulator must not only be a good insulator electrically but it also must have sufficient mechanical strength to counterbalance the forces due to tension of the line conductors. (See Figure 93).

Figure 93 – Strain insulator.

7.10.4 Spool Insulators

The spool insulator (shown in Figure 94) is used to support the system neutral or secondary wires. Spool insulators never support high voltage wires. You will most often see spool insulators mounted directly to the pole with a clevis supporting distribution system neutrals.

Figure 94 – Spool and clevis.

7.11.0 Conductors

The wires and cables which transmit electrical energy are made of copper, aluminum, steel, or a combination of copper and steel or aluminum and steel. A conductor is a

material that readily permits the flow of an electric current. Materials that conduct electricity, other than those mentioned, are not generally used to make wires and cables for economic or physical reasons.

7.11.1 Copper Conductors

Copper is the most commonly used line conductor. It conducts electrical current very readily, ranking next to silver. It is very plentiful in nature, can be easily spliced, and its cost is comparatively low. Three kinds of copper wire are in use: hard-drawn copper, mediumhard- drawn copper, and annealed copper, also called "soft drawn."

For overhead line purposes, hard-drawn copper wire is preferable on account of its greater strength. Medium-hard-drawn copper can be used for distribution lines usually for wire sizes smaller than No. 2.

7.11.2 Aluminum Conductors

Aluminum is widely used for distribution and transmission line conductors. Its conductivity, however, is only about two thirds that of copper. Compared with a copper wire of the same physical size, aluminum wire has 60 percent of the conductivity, 45 percent of the tensile strength, and 33 percent of the weight. The aluminum wire must be 100/60 = 1.66 times as large as the copper wire in cross section to have the same conductivity. When an aluminum conductor is stranded, the central strand is often made of steel that serves to reinforce the cable. Such reinforcement gives added strength for the weight of conductor. Reinforced aluminum cable called ACSR (aluminum-conductor steel-reinforced) is especially suited for long spans.

7.11.3 Copperweld Steel Conductors

In this type of conductor, a protective copper coating is securely welded to the outside of the steel wire. The copper acts as a protective coating to the steel wire, thus giving the conductor the same life as if it were made of solid copper. At the same time, the layer of copper greatly increases the conductivity of the steel conductor, while the steel gives it greater strength. This combination produces a satisfactory yet inexpensive line conductor. Its chief field of application is for rural lines, guy wires, and overhead ground wires.

The conductivity of copper-weld conductors can be raised to any desired percentage, depending on the thickness of the copper layer. The usual values of conductivity of wires as manufactured are 30 and 40 percent.

7.11.4 Classes of Conductors

Conductors come in two classes, solid and stranded. A solid conductor is a single conductor of solid circular section. A stranded conductor is composed of a group of small conductors in common contact. A stranded conductor is used when the solid conductor is too large and not flexible enough to be handled readily. Large solid conductors are also easily damaged by bending. The need for mechanical flexibility usually determines whether to use a solid or a stranded conductor, and the degree of flexibility is a function of the total number of strands. The strands in the stranded conductor are usually arranged in concentric layers about a central core. The smallest number of wires in a stranded conductor is three. The next number of strands is 7, 19, 37, 61, 91, 127, and so forth. Both copper and aluminum conductors may be stranded.

7.11.5 Conductor Sizes

Conductor sizes are ordinarily expressed by two different numbering methods: the American Wire Gauge (AWG) and the circular mil. The AWG conductor sizes are numbered from 30 to 1, and then continue with 0, 00, 000, and 0000 (or 1/0, 2/0, 3/0, and 4/0, respectively). Number 30 is the smallest size and 4/0 the largest in this system. As an example of the actual physical size of the conductors commonly used in transmission and distribution work, refer to Figure 95. Refer to Course 9 of the NEC for complete table listings.

The circular mil is the unit customarily used in designating the cross-sectional area of wires. A "circular mil" is defined as the area of a circle having a diameter of 1/1000 of an inch. The circular mils of cross section in a wire are obtained by squaring the diameter expressed as thousandths of an inch. For example, a wire with a diameter of 0.102 inches (102 thousandths of an inch) has a circular mils cross section of 102 x 102 = 10,404. Conductors larger than 4/0 AWG are designated in circular mils. These range from 250,000 to 2,000,000 circular mils (250 MCM or 2,000 MCM).

Figure 95 – American wire sizes for bare copper.

7.12.0 Installing Conductors

There are several acceptable methods for stringing out and raising conductors. The method you use depends upon where the new pole line is located and what kind of equipment is available to you. You may place the wire reels on a truck or wire trailer and drive along the right of way unreeling the wire, or you may use the running block or over the crossarm methods.

7.12.1 Mounting the Reels

No matter how you string the wire, you will have to mount the reels on some support that allows them to revolve freely. Usually you do this by raising a reel on reel jacks, as shown in Figure 96. Put a metal rod strong enough to support the reel through the hole in the center, and jack up the rod and reel on each side. You may have to fasten down the bases of the jacks to keep the strain from upsetting the reel. When you are jacking up, it is necessary only to raise the reel just clear of the deck.

Figure 96 – Cable reel on reel jacks.

When you are stringing wire in rough terrain, the best method is to anchor a reel to the ground at the end of the line by means of guys run to driven stakes. Then run a rope line over the crossarms or through running blocks mounted on the crossarms for a distance of 1,000 to 1,500 feet. A lineman accomplishes this by climbing each pole and placing the rope in place.

After stringing the rope over the crossarms, secure one end to the wires to be pulled, and take a couple of turns with the other end around the winch drum on the line truck. Then rotate the drum to haul in the rope and the wires with it. As each wire passes a crossarm, a lineman must climb the pole to set the wire in proper position and guard against twisting.

To keep a paying-out reel from revolving too fast, set a brake or drag against the reel. This can be simply a board, held against the outer edge of the reel by a helper. As a wire or wires are being pulled, enough crew members must be stationed along the way to establish a chain of signal communication from the head of the line back to the line truck.

Pull several feet past the last dead-end pole to ensure there is enough conductor for sagging and cut the conductor at the reel.

7.12.2 Placing the Neutral Conductor

Always place a neutral conductor on a center crossarm insulator or on a pole-top insulator. Butting the neutral on a center pole insulator gives the lineman a clear space around the pole to climb through; that is, it ensures that the hot wires are a considerable distance apart.

7.12.3 Pulling In Conductors

When the conductors have been hoisted in place on the crossarms and dead-ended on one end, you are ready to start "pulling in"; that is, heaving on the conductors until each has been raised to proper sag. You can do this with a tackle equipped with conductor grips or individually, using a conductor grip and a come-along.

A conductor grip is a clamp device that grips the wire tightly when a strain is applied to the grip. When you are pulling two or more wires at once, it is best to use the equalizer. This device distributes the strain equally on all the wires.

7.12.4 Measuring the Sag

When wires have been pulled to approximately the desired sag, a lineman goes to the center span to measure the sag. Measurement at the center of each span ensures uniformity. Three common ways of measuring sag are by dynamometer, by timing vibration, and by the use of targets.

7.12.4.1 Dynamometer

Alever-cam dynamometer is an instrument that is installed in the pulling line and that measures the strain of the pull. Use it in conjunction with a chart that gives the desired pull tension for a given conductor size, span length, and temperature. A traction dynamometer, also installed in the pulling line, provides direct readings on the face of the dial.

7.12.4.2 Timing Vibration

The timing-vibration process is done by striking the wire sharply near one of he pole supports and timing with a stopwatch the interval that elapses as the impulse from the blow ravels to the next pole and returns. This system is not accurate when wind is swinging the line or when someone is working on the line in an adjacent span.

7.12.4.3 Targets

The target-sighting method is a simple and accurate means for measuring sag. Target- measure sag by nailing slat targets, such as a couple of pieces of wood lath, at the point on each pole below the conductor insulator. A lineman then sights from one slat to the other.

7.12.5 Sagging Procedures

7.12.5.1 Purpose

Once the conductor is positioned, you must sag and secure it. Properly sagging the conductor allows for expansion and contraction during temperature changes. It also minimizes strain on the pole and related hardware and aids in maintaining conductor spacing in high winds.

7.12.5.2 Sagging Chart

To determine the proper sag for your conductors, consult a sagging chart. The chart will reference the conductor type, ruling span length (both found on the staking sheet) and the outside temperature to determine how much your conductors should sag in the middle of the span. See Table 3.

Table 3 – Sagging chart.

No.
(AWG)
Temperature
(Degrees F)
Sag in inches for span lengths of

100 ft

125 ft 150 ft 175 ft 200 ft 250 ft
6
30
60
90
 5.8
 8.0
12.0
 8.5
12.0
17.0

13.5
18.0
23.5

18.5
24.0
30.0

-- --
4
30
60
90
 5.8
 8.0
12.0
8.5
12.0
17.0
13.5
18.0
23.5
18.5
24.0
30.0
25.0
32.0
39.0
25.0
42.0
50.0
2
30
60
90
 5.8
 8.0
12.0
8.5
12.0
17.0
13.5
18.0
23.5
16.5
22.0
28.0
20.0
26.0
33.0
29.5
36.0
44.0
1
30
60
90
 5.8
 8.0
12.0
8.5
12.0
17.0
13.5
18.0
23.5
15.5
20.0
27.5
28.5
24.0
31.0
24.5
31.0
39.0
0
30
60
90
  5.8
  8.0
12.0
8.5
12.0
17.0
13.5
18.0
23.5
15.5
20.0
27.5
18.5
23.5
29.5
23.5
29.0
36.0
00
30
60
90
 5.8
 8.0
12.0
8.5
12.0
17.0
13.5
18.0
23.5
15.5
20.0
26.0
17.5
22.0
28.0
21.0
27.0
34.0
0000
30
60
90
5.8
8.0
12.0
8.5
12.0
17.0
13.5
18.0
23.5
14.5
19.0
25.0
16.5
21.0
27.0
19.5
24.0
30.0
7.12.5.3 Sagging the Conductors

Once you have determined the amount of sag by consulting a sagging chart, you are ready to sag the conductors. Begin by securing all the conductors to one end of the pole line. Do this by clamping the conductors into a dead end “shoe” (See Figure 97), then affixing the shoe to the suspension insulator on the dead end pole.

Figure 97 – Dead-end shoe.

Once you have secured the conductors at one end of the pole line, proceed to the dead end pole at the other end of the pole line. Hang a dead end shoe from the suspension insulator you will sag first. This will be the top conductor if you are using armless construction or one of the outside conductors if you are using crossarm construction.

Hang a small block and tackle from the ring on the dead end shoe. The ground support person will then attach a conductor grip to the conductor and raise it on the handline. A conductor grip works like a guy wire grip, except conductor grips do not have teeth in the jaws. Teeth would damage the conductor, so the jaws are smooth. Never use a guy wire grip on a conductor.

Attach the other end of the small block and tackle to the conductor grip, (see Figure 98) and remove the handline. The conductor is now suspended from the suspension insulator by the small block and tackle, which the climber can adjust in and out to get the proper amount of sag.

Figure 98 – Conductor grips.

There are several methods to achieve the correct amount of sag; the sighting method (see Figure 99) will be presented here. This entails mounting dowels or similar thin strips of wood (called firring strips) to two utility poles, below the tops of the insulators at a distance equal to the desired amount of sag. When the two firring strips are in place, an electrician can sight along the top of the strips and adjust the conductor until it intersects with their line of sight. Thus, if the firring strips are mounted 12 inches below the tops of the insulators, when the conductor intersects the line of sight, it will be sagging 12 inches in the middle of the span.

Figure 99 – Sighting method of sagging.

Adjust the conductor with the small block and tackle until it reaches the proper sag. Then secure the conductor in the dead end shoe, and remove the small block and tackle along with the conductor grip. Then repeat the process for the remaining conductors

After the wires are "sagged in," allow a rest period of from 1/2 hour to 4 hours (varying according to the length of the pull) to let the wires adjust themselves to the tension in the pull. They will gradually "creep" until tension in all the spans is equalized. After they have crept to the final position, you are ready to "tie in."

Figure 100 shows the effect of temperature on the sag in a 200-foot span of 00 wire.

Figure 100 – Effect of temperature on sag in 200 foot span of 00 wire.

7.12.6 Tying in Conductors

7.12.6.1 Purpose

Once the conductors are properly sagged, you must secure them on the insulators using conductor ties. Conductor ties keep the conductors on the insulators, and maintain proper sag.

7.12.6.2 Types and Procedures

When installing conductor ties, you have the choice of using a preformed tie wire or fabricating the ties by hand. Always use new, fully annealed wire for ties. Harddrawn wire is brittle and cannot be pulled up against the conductor and insulator.

 

Note

When using an aluminum conductor, you are required to cover it with armor rod at each insulator to provide physical protection against rubbing or pitting caused by the elements. These armor rods are wrapped on the conductor by hand and require no special tools. Another important requirement is the use of ACSR-rated deadend shoes, splice connectors, and all other devices that come in direct contact with an aluminum conductor. This is to prevent electrolysis from the physical contact of dissimilar metals.

7.12.6.2.1 Preformed Conductor Tie

Preformed tie wires (shown in Figure 101) work on the same principle as preformed guy wire wraps. They are installed on the insulator and then wrapped around the conductor, holding it tight. Preforms are a very quick and easy way to secure conductors to insulators, but they are not “one size fits all.” Preforms must be ordered for specific size/type insulators and specific size/type conductor.

Figure 101 – Preformed conductor tie.

7.12.6.2.2 Hand Fabricated Tie

To fabricate a conductor tie by hand, use a piece of soft-drawn tie wire as seen in Figure 102. Use aluminum tie wire for aluminum conductors (including ACSR), and copper tie wire for copper conductors. You will use #2, #4 or #6 AWG tie wire, depending on the size of the conductor. The two

basic types of ties are the top tie and the side tie, and the conductor’s position on the insulator will determine the type of tie made.

Cut a six- foot piece of soft-drawn tie wire and wrap it around a 2 inch pipe, a soda can, or your hand to form a coil of wire. Separate the coil in the center to create what you see in Figure 102. This shape makes it easier to handle while on the pole. When forming your tie on the insulator, keep in mind that the key to a good tie is to wrap it as tightly as you can.

Figure 102 – Tie wire.

Top Ties

Use top ties (see Figure 103) to secure the conductor when it is in the top groove of the insulator. You use top ties on poles where there is no angle change.

Figure 103 – Top tie – 2 buttons on each side.

Use the following steps to fabricate a top tie:

  1. Center the tie wire on the backside of the insulator. Pull the coiled ends toward you. Both sides of the wire should be of equal length and under the conductor.
  2. Wrap two close wraps around the conductor on each side. These close wraps are referred to as “buttons.” (Shown in Figures 7-103 and 7-104).

Figure 104 – Top tie – 4 buttons on each side.

  1. Cross the right end to the left and left end to the right around the front of the insulator. Pass the tie wire below the conductor. Make two more buttons on each side.
  2. On each side of the insulator, wrap six 1 inch spaced, spiral wraps. Bend the ends back and cut off the excess tie wire. (See Figure 105)

Figure 105 – Top tie.

Side Ties

Use the side tie when the conductor pulls against the side of the insulator. This occurs on pin insulators when there are line angle changes. You will also use the side tie on spool insulators. Use the following steps to fabricate a side tie.

  1. Center the tie wire on the backside of the insulator. Pull the coiled ends toward you. Both sides of the wire should be of equal length and under the conductor. (See Figure 106)

Figure 106 – Side tie – 2 buttons on each side.

  1. Make two buttons on each side of the insulator.
  2. Cross the right end to the left and left end to the right around the back of the insulator. Pass the tie wire below the conductor. Make two more buttons on each side. (See Figure 107)

Figure 107 – Side tie– 4 buttons on each side.

  1. On each side of the insulator, wrap six 1 inch spaced, spiral wraps. Bend the ends back and cut off the excess tie wire as seen in Figure 108)

Figure 108 – Side tie.

7.13.0 Protective Devices

Transformers and other equipment on pole lines are very expensive to purchase and very time-consuming to install. To keep them in good working order, you must protect them from overcurrent and overvoltage conditions. You do this by installing protective devices.

7.13.1 Purpose

You must protect transformers from overvoltage and overcurrent conditions that can cause damage. The two devices that provide this protection are lightning arresters (shown in Figure 109) and fuse cutouts. (See Figure 110)

Figure 109 – Lightning arrestor.

7.13.1.1 Lightning Arresters

The purpose of lightning arrestors is to protect against overvoltage. They provide a low impedance path to ground for lightning and transient over voltages, such as those arising from operating high voltage switches, without injury to line insulators, transformers, or other connected equipment. When there is an overvoltage condition, the lightning arrestor provides a path to ground to drain off the excess voltage. Once the overvoltage condition has dissipated, the arrestor restores the circuit to a normal condition and prevents the further flow of current to ground. Overvoltage protection is only one function of protective devices; you must also protect against overcurrent conditions.

Lightning arresters are designed to permit normal circuit operations at designed voltages. Lightning arresters are essential in all areas of power line construction. These include distribution, secondary, intermediate, and station distribution. The four different specifications of arresters, mentioned above, have different spark over voltages, current discharge capabilities, and maximum surge discharge capabilities.

Secondary arresters are used on service and other low-voltage alternating-current circuits. Distribution arresters are used on primary distribution systems to protect insulators, distribution transformers, and other equipment. The intermediate type of lightning arrester is often used on substation exit cables and other locations on the distribution system needing a high level of lightning and surge protection. Substation types of arresters are used in substations and generating stations to provide a high level of surge protection for the major pieces of equipment. Surge voltages can be generated by operating switches in the electric transmission system as well as by lightning.

Various types of lightning arresters are in use today. The valve, pellet, and air gap are the most common and likely-to-be-seen types in the field.

7.13.1.2 Fuse Cutout

The purpose of fuse cutouts is to protect against overcurrent. Fuse cutouts are inexpensive protective devices put in the circuit to open the circuit when an overcurrent condition occurs. The fuses are made from a short piece of wire, which is a weak link intentionally placed in the circuit. When this wire heats up due to overcurrent, it melts. This is commonly referred to as “blowing the fuse.” This creates an open, which de- energizes the connected equipment to prevent or limit damage from current overloads and short circuits. See Figure 110.

Figure 110 – Fuse cutout.

7.13.2 Types of Protective Devices

7.13.2.1 Lightning Arrestor

Lightning arrestors have evolved over the years. The valve type arrestor, seen in Figure 109, is the most common type in use today, and consists of a porcelain or polymer (plastic) housing filled with silicon carbide or metal oxide valve blocks.

These valve blocks act as non linear resistors, which keep normal line voltage from passing through the arrestor but conduct surge voltages to ground. The valve-type arrestors using metal oxide valve blocks are the most modern, and provide more precise control of the voltage level at which the arrestor begins conducting surge voltages to ground.

Valve type arrestors are normally equipped with an isolation device, the function of which is to separate the ground lead from the arrestor if the arrestor should fail. In Figure 109, the black portion on the bottom of the arrestor is the isolation device. If the arrestor fails to limit normal line voltage from flowing to ground through the arrestor, the isolation device will heat up due to current flow, and an explosive rivet will blow the ground lead clear of the arrestor. This is the only visual indication an electrician has of a problem with the arrestor.

The valve type arrestor comes in four classes: secondary, distribution, intermediate, and station. Secondary arrestors are used on low voltage circuits ranging from 175 to 650 volts. The distribution arrestors are the most common and range from 3 to 30 KV. These are used to protect transformers and other equipment. Intermediate arrestors are used on substation exit cables and where high levels of surge protection are needed. They range in size from 3 to 120 KV. Station type arrestors are used in substations and generating stations for protection of major equipment and range are 3KV and higher.

7.13.2.2 Fuse Cutout

Anything worth protecting from overvoltage is worth protecting from overcurrent. A fuse cutout (see Figure 111) provides this protection. Like lightning arrestors, fuse cutouts have evolved over the years. There is more than one variety in use, but the one we are going to discuss is the “open type” which is the type most commonly used on overhead distribution lines today.

Figure 111 – Fuse and fuse cutout.

The open type distribution cutout houses the actual fuse link in a barrel, as shown in Figure 111. When the fuse link blows, the barrel swings down, creating an easily visible indicator. The fuse links come in two different types: “K” (kwick) and T (tardy). The K type fuse provides a means of protection against instantaneous fault currents. The T type fuse will withstand the rated current for a set period of time before it will blow.

7.13.3 Sizing of Protective Devices

Before installing a protective device in your distribution system, you must know what voltage and/or current ratings are required of the distribution system.

7.13.3.1 Lightning Arrestor

A lightning arrestor is sized according to the voltage of the wire it is protecting.

Wye System. On a wye system you multiply the phase voltage by 1.25. For example: on a wye system of 7200/12470 VAC the phase voltage is 7200 VAC. Multiply this by 1.25 (7200 X 1.25) to give you 9000. Use a 9kV lightning arrestor.

Delta System. On a delta system the arrester must be equal to or greater than the line voltage. If you have a delta circuit of 13,800 VAC, your lightning arrestor has to be equal to or greater than13,800 VAC. If an arrestor is not available in the exact voltage you need (like 13,800), go with the next-largest size.

7.13.3.2 Fuse Cutouts

Fuse cutouts are sized according to voltage and amperage. The cutout should be sized according to the voltage of the system in which it is installed, while the fuse it holds should be sized according to the Full Load Current of the equipment it is protecting. To determine the proper size fuse, consult a fusing chart in one of the reference books in your shop, such as The Lineman’s and Cableman’s Handbook. A good practice is to print up a chart of proper fuse sizes (see Table 4) and keep it in the truck or your tool bag.

Table 4 – Fuse size chart.

FUSE SIZES
KVA 12,470Y / 7200 12,470 12,470
Wye primary
1- and 3-phase
Delta primary
single phase
Delta primary
three-phase
 3 1 1 1
5 1 1 1
1 2 1 1
15 3 1 3
25 5 3 5
37.5 6 5 6
50 8 6 10
75 12 8 12
100 15 10 15
167 30 15 30
250 40 25 50
333 50 30 65
500 80 50 80

7.13.4 Installation Procedures

Lightning arrestors and fuse cutouts are mounted together, either on a crossarm or armless hardware. Mount the devices as close as possible to the phase to which they will be connected and to the equipment they are protecting. This keeps the jumper wires short. Ensure that when you mount the fuse cutout, it has sufficient room to allow the fuse barrel to swing freely.

If mounting to a crossarm, use L brackets (shown in Figure 112) and carriage bolts. If mounting to armless hardware, simply bolt to the standoff arm.

Figure 112 – L-brackets.

7.13.5 Connection Procedures

When making connections on protective equipment, use soft- or medium drawn wire. Either copper or aluminum is acceptable. Make the wires as short as possible.

7.13.5.1 Lightning Arrestor

Connections on a lightning arrestor are simple. Connect the top of the arrestor to the primary phase with a hotline clamp. Connect the bottom of the lightning arrestor to the pole ground with a compression fitting or a split-bolt connector.

7.13.5.2 Fuse Cutout

To connect a fuse cutout, install a jumper wire from the top of the fuse cutout to the top of the lightning arrestor. (See Figure 113)

Figure 113 – Protective device connections.

 

Note

One piece of wire is often used to connect both the fuse cutout and the lightning arrestor to the primary phase. Connect the bottom of the fuse cutout to the H1 bushing on the transformer.

 

7.14.0 Grounds

Grounding in the power distribution system is important. The grounding system protects you and the distribution system when faults occur and aids in the suppression of noise. Grounds are required every quarter mile on a power distribution line and at every pole when equipment, such as transformers, regulators, capacitors, switches, circuit breakers, and lightning arresters, is installed. The maximum resistance of any distribution ground is 25 ohms, but a lower resistance is desired.

7.14.1 Installing Grounds

The electrical configuration of the primary distribution system, (Wye or Delta), will determine how to install the grounding system. Wye connected electrical distribution systems should be provided with a grounded neutral connection. The neutral wire is physically connected to earth with a wire that runs down the pole and either attaches to a ground rod or is wrapped around the butt of the pole. Such intentional grounding minimizes the magnitude and duration of over voltages, thereby reducing the probability of insulation failure and equipment damage.

Where systems are delta-connected, no ground will be provided. Neutrals for each voltage level should be grounded independently at each electric power source, at transformer secondaries and at generators.

7.14.1.1 Connecting to the Neutral

The two common ways to connect a grounding conductor to the system neutral in a Wye connected electrical distribution systems is by way of a split bolt connector or a compression (sometimes called a “crimp”) connection. The preferred method is to use a compression connection, as it provides a tighter connection and requires no maintenance. Split-bolt connectors have to be periodically re-tightened.

The ground conductor shall have an ampacity of not less than 1/5 that of the conductor (neutral) to which it is attached. A common size ground conductor used for the system ground is No. 6 AWG soft-drawn copper. This is the same size conductor often used for lightning arresters, pole grounds, and transformer (case) equipment grounds.

7.14.1.2 Connecting to the Equipment Ground

If system and equipment grounds are on the same pole, they are bonded together and will usually share the same down conductor. All equipment mounted on poles are required to be grounded and will have some type of connection terminal built in for this purpose. Connections are made with the down conductor using these terminals.

7.14.1.3 Connecting to the Pole

The down conductor is secured to the pole using in one inch staples. The staples are hammered in place at 2 foot intervals along the length of the pole. (See Figure 114) Locate the grounding conductor on the same side of the pole as the neutral and in a quadrant opposite the climbing space (face) of the pole.

Figure 114 – Pole ground.

7.14.1.4 Connecting to the Grounding Electrode

In general, use a minimum 5/8 inch diameter, 8 foot long copper-clad ground rod as the ground electrode. Install the rod 1 to 2 feet away from the pole, and drive the rod until its top is 2 feet below the surface. Attach the down conductor to the ground rod using an exothermic weld, a compression connector, or a ground rod clamp. The exothermic weld is the preferred method of connection since it is a maintenance free connection. See Figure 115.

Figure 115 – Exothermic weld.

Since the resistance of the earth varies, depending upon the soil’s composition, moisture content, and temperature a singular ground rod may not enable you to obtain the required ground resistance of 25 ohms or less.

When one ground rod does not provide the required ground resistance, you will have to install additional ground rods or use longer rods as necessary. The space between additional ground rods should never be less than six feet. Since the ground’s resistance usually decreases with depth (because of increased moisture), the use of longer ground rods is normally the first approach you will want to take to obtain a suitable resistance reading. The reason is purely a matter of economics.

Another option available in obtaining a suitable ground is to make a connection of the down conductor to metallic-water pipes. While connections to a metallic-pipe water system usually provides a very low ground resistance, there is the possibility that water pipe maintenance or other work might result in accidental disconnection of grounds and create a hazardous condition. Therefore, such connections should only be provided as a secondary backup to driven ground rods.

In areas of very low soil resistivity, you may use butt wraps (see Figure 116) and butt plates; however, only use these types of grounding electrodes as system grounds (a ground rod must be installed for all equipment grounds). A butt wrap is a spiral of wire placed on the bottom of the pole. It starts at the outside circumference of the butt and circles inward making seven turns. The coil is “shorted out” to itself to prevent it from acting as an inductor which would try to limit current flow. Shorten it by stapling the ground wire to each coil as it crosses on its way back out to the edge of the pole. It starts at the outside circumference of the butt and circles inward making seven turns. The coil is “shorted out” to itself to prevent it from acting as an inductor which would try to limit current flow. Shorten it by stapling the ground wire to each coil as it crosses on its way back out to the edge of the pole. The process of installing a butt ground on a pole is obviously something that needs to be done prior to setting the pole in the ground.

Figure 116 – Pole with butt ground plate.

The process of installing a butt ground on a pole is obviously something that needs to be done prior to setting the pole in the ground.

7.15.0 Transformers

Transformers are an essential part of any overhead distribution system. Without transformers, you could not provide useable power to the customer. See Figure 117.

Figure 117 – Pole mounted transformers

7.15.1 Pre-installation Considerations

Before installing a transformer into a distribution system, you need to conduct a few checks.

7.15.1.1 Proper Voltage Ratings

Check the data plate on the transformer (the data plate is a steel tag the manufacturer attaches to the transformer that lists all the important information about the transformer) to ensure the high voltage rating matches your system voltage and the low voltage rating matches the customer’s needs. Also, ensure the KVA of the transformer is sufficient to supply the load.

7.15.1.2 Condition of the Unit

Regardless of whether the transformer is new, rebuilt or used, always check the condition of the unit before installing it.

7.15.1.2.1 Electrical

Use a megohmeter (also called a megger) to test the windings of the transformer for faults. A megger is just a high powered ohmmeter, used to measure very high resistance. In this application, you will be using it as a continuity tester to determine if any of the windings in the transformer are open, shorted, or grounded.

To test the primary winding for opens, connect the megger to the primary bushings. If the megger measures zero resistance (meaning there is a continuous piece of wire from one bushing to the other, with no resistance to the flow of electricity), then there is no open. (See Figure 118) If the megger reads infinity (the megger reads an infinite amount of resistance because there is no path for electricity to flow) that means there is an open in the winding. (See Figure 119)

Figure 118 – Checking primary - no opens.

Figure 119 – Checking primary – open.

Test the secondary windings for opens in the same way you checked the primary winding. If the secondary windings are connected in series, you can test both at the same time. Again, a megger reading of zero indicates that there is no opens in the winding. (See Figure 120) A megger reading of infinity means there is an open, and the transformer is unusable. (See Figure 121)

Figure 120 – Checking secondary – no opens.

Figure 121 – Checking secondary – open.

When testing for a short, you are checking to see if the primary winding and the secondary winding are touching. The windings are wound together in layers on the core of the transformer, insulated from each other by a thin coating of varnish and oil-impregnated paper. If the insulation fails, the transformer will not work properly, and could even explode if the short is bad enough. To test for a short, connect one lead of the megger to the primary winding and connect the other lead to the secondary winding. A reading of infinity means there is no short, meaning the windings are not touching and there is no path for electricity to flow. (See Figure 122) A reading of zero means the windings are shorted (see Figure 123) together and the transformer is unusable.

7-122 – Windings not shorted

Figure 123 – Windings shorted.

Checking for a ground means you are testing to see if one of the windings is touching the case of the transformer, which will be connected to ground when it is installed. You test for a grounded winding by connecting one lead of the megger to the transformer case and connecting the other lead to each of the windings. A reading of infinity means there is no ground (Figure 124); a reading of zero means the winding you are connected to is grounded (Figure 125) to the case, and the transformer is unusable.

Figure 124 – Testing primary – no ground.

Figure 125 – Testing secondary – ground.

7.15.1.2.2 Oil

Before installing and applying power to any equipment that is filled with oil, test the oil in an oil tester to make sure it retains the proper di-electric strength. If the oil is contaminated, it will not insulate properly and the equipment will be damaged or destroyed if voltage is applied to it. The oil is tested between two circular electrodes set in a test cup. Space the electrodes one-tenth of an inch apart, and apply and increase voltage until an arc jumps across the electrodes. The voltage level at which this happens is an indication of how much dielectric strength the oil has. When you dielectrically test oil:

  1. Take sample from the bottom of the oil tank. This will be the most contaminated oil, and you want to check the worst of the oil (if the worst of the oil passes, you know the remaining oil will also pass).
  2. Allow the sample to sit for at least 8 hours to allow air bubbles to dissipate.
  3. Before filling test cup, gently swirl sample jar to distribute impurities (do not shake – this will introduce air bubbles).
  4. Slowly fill test cup to a level not less than 2 centimeters above the electrodes.
  5. Place cup in tester and allow to stand not less than two minutes or more than three minutes.
  6. Apply voltage and increase (no faster than 3000 volts/second) until an arc jumps across the electrodes, and note the reading on the voltmeter.
  7. Empty test cup into second sample jar for return to transformer.
  8. Repeat steps 4-7 for a total of five tests.

Check for consistency in readings. If readings are consistent, average the five readings and compare the result to a chart such as the one shown in Table 5. This chart was developed by the ASTM.

Table 5 – Acceptable breakdown values.

DIELECTRIC BREAKDOWN VOLTAGE

NEW OIL AS REC'D 28KV MIN/36KV AVG
NEW OIL PROCESSED 30KV MIN/36KV AVG
NEW OIL TAKEN FROM NEW EQUIPMENT 30KV MIN/36KV AVG

OIL FROM EQUIPMENT IN SERVICE

 
69KV AND BELOW 25KV MIN
69KV TO 288KV 29KV MIN

If the oil does not meet the minimum requirements, it must be replaced or filtered to remove impurities. Ensure the oil is at the proper level before putting the transformer into service.

7.15.1.2.3 Mechanical

Once you complete the electrical tests and verify the condition of the oil is, check the mechanical condition of the unit. Check for cracked or leaking bushings, cracked welds and rust. Ensure the mounting brackets are not bent, and the lift points are in good condition.

7.15.2 Installation Locations

When CE’s conduct overhead construction, transformers are usually installed on the utility poles, but occasionally they may be mounted on concrete pads. When more than one transformer is mounted to a pole, the weight must be distributed equally on both sides of the pole.

7.15.2.1 On Poles

Transformers can be mounted directly to the pole. This type of installation is the cheapest way to install a transformer because it requires very little hardware. The size and weight restrictions depend largely on the class of the pole. Three phase transformer banks (consisting of three single phase transformers wired together) can be installed on a pole by using a cluster bracket. Cluster brackets come in two types: through-bolt and radial (sometimes called wrap around). The through-bolt bracket mounts on two through bolts installed in the pole. The radial bracket requires no holes to be drilled; it is clamped around the pole and tightened, squeezing the pole. Up to three 100 kVA transformers can be installed using a cluster bracket. See Figure 126.

Figure 126 – Pole mounted transformers.

7.15.2.2 On Pads

Even in an overhead distribution system, transformers are sometimes placed on concrete pads. This requires a riser pole to transition the overhead primary phases to underground cable, which is then run to the pad. The main benefit of mounting on a pad is that any size transformer can be placed on a pad. An added benefit is that a pad mount transformer being fed from underground makes for a more attractive installation.

7.15.3 Installation Methods

Transformers can be installed directly to poles using either the manual method or the truck method. The equipment available to you, as well as the location of the work, will determine what method you use. To install a transformer manually, you will need a transformer gin, as shown in Figure 127, a large block and tackle, a transformer sling, and a tagline. If you use a truck to install a transformer, you will need a transformer sling and a tagline.

Figure 127 – Transformer gin.

7.15.4 Installation Procedures

7.15.4.1 Manual

To install a transformer to a pole manually, gather the equipment listed above, along with hand tools, a handline, and mounting hardware (two through-bolts, two flat washers, two nuts). The climber ascends the pole to the appropriate working height and belts in. He/she will then install the handline above the work area in order to raise and lower equipment and tools.

Consult the specification sheet, and drill the holes for the two through-bolts in the proper location. Use a brace and bit to drill the holes from the side of the pole where you will install the transformer. When you have drilled both holes, raise the transformer gin and install it directly over the through-bolt holes as high as possible.

Raise the block and tackle next and hang it in the ring of the transformer gin. Install the throughbolts so the bolt heads extend 2 inches. on the transformer side of the pole. No washers are required under the bolt heads. Ensure the through bolts are the proper length; no more than 2 inches. of a through-bolt should extend from the pole after tightening. While the through bolts are being installed, the ground support person can prep the transformer to be raised.

Move the transformer to the base of the pole directly below where you are going to install it. When you move a transformer, NEVER lift it by the bushings. In order to raise the transformer, you must hook a transformer sling over the lifting points and then attach it to the block and tackle. You must also attach the tagline using a timber hitch.

The ground support person raises the transformer with the block and tackle, while guiding it away from obstructions on the pole by using the tagline. When it is within reach, the electrician on the pole will help guide the transformer until the mounting brackets are slightly above the through bolts. The climber directs the ground support person to raise or lower the transformer while he/she guides the mounting brackets to capture the heads of the through bolts.

With the through bolt heads captured in the mounting brackets and the weight of the transformer on the through bolts, the climber tightens the top bolt and then the bottom bolt. When the transformer is secure, the lifting equipment can be removed.

7.15.4.2 Truck

Installing a transformer using a truck differs from a manual installation only in the method of raising the transformer. All procedures are the same, except the ground support person raises the transformer with the winch line of the truck instead of a block and tackle.

7.16.0 Service Drops

Service drops are a critical part of delivering electricity to our customers. The service drop conductors take power from the transformer and distribute it to the various loads. This section will explain the purpose and application of this critical portion of your distribution system.

7.16.1 Purpose of the Service Drop

The purpose of a service drop is to distribute the low voltage (secondary) from the transformer to the customer(s).

7.16.2 Types of Service Drops

7.16.2.1 Single-Phase

Single phase service drops are used mostly for residential housing and streetlights. The term “single phase” refers to the fact that the service drop is distributing power from a single phase transformer. Since single phase distribution transformers can provide one or two voltages, single phase service drops can be one phase and a neutral or two phases and a neutral.

7.16.2.2 Three-Phase

Three phase service drops are used mostly for industrial and commercial areas. The term “three phase” refers to the fact that the service drop is distributing power from a three phase transformer or from three transformers connected together to give three phase power. Facilities with large lighting loads or large motor loads require three phase power. A three phase service drop will have three conductors and may also have a neutral.

7.16.3 Pre-installation Considerations

7.16.3.1 Types of Conductors

Before installing a service drop, consider the type of conductor best suited to your needs. A service drop is merely a bundle of conductors. You can hang these conductors as several single conductors or use “plex” conductors. If the secondary will use very large conductors (due to a large amount of current), you will want to use a single- conductor installation. If the load is not very large, plex conductors are the wise choice.

Single Conductors. Single conductors are used for large secondary loads. The large load requires large conductors and this makes a plex conductor arrangement too awkward to handle.

Plex Conductors. Plex conductors consist of a piece of ACSR with one, two, or three insulated aluminum conductors twisted around it. The ACSR holds the weight of the entire assembly and acts as the neutral, while the insulated conductors carry the low voltage to the customer.

If there is one insulated conductor and one bare piece of ACSR, it is called duplex. Triplex is two insulated conductors wrapped around one bare ACSR conductor.

Quadraplex is three insulated conductors wrapped around one bare ACSR conductor.

7.16.3.2 Size of Load

The size of the load determines the size of the conductor you will install. The conductor must be large enough to safely carry the amount of current the customer needs.

7.16.3.3 Span Length

Another consideration is span length. Span length is the distance a conductor runs between two supports. The maximum span length for a service drop is 125 feet. If the span is longer, it requires an intermediate support pole.

7.16.3.4 Clearances

Base the clearance height for conductors on both the voltage they carry and where they are located. Service drops not subject to vehicular traffic require a minimum clearance of 12 feet Service drops that span an alley or a street require a minimum clearance of 16 feet The clearance is measured at the lowest point of the sag.

7.16.3.5 Attachment Devices

The last pre installation consideration is how to secure the service drop. You can use a number of different attachment devices to secure service drops.

Spool Racks. Spool racks are rows of spool insulators placed on a steel support that separate the spools and provide an attachment point to poles or other supports. (See Figure 128) Spool racks are used for single conductor installations. Attach the conductor to the spool by passing the conductor around the insulator and wrapping it back onto itself.

Figure 128 – Spool rack.

Clevis. A clevis and spool insulator, as seen in Figure 129, are commonly used to support plex conductors. You will most often see spool insulators mounted directly to the pole with a clevis supporting distribution system neutrals.

Figure 129 – Clevis.

Installing a clevis and spool insulator is relatively simple. you can see that a through bolt is fitted through the clevis. Mount the through bolt/clevis assembly to the pole, and then secure the spool insulator in the clevis with a clevis pin and cotter key. Be sure to correctly orient the spool insulator with the grooved end on top and drop the clevis pin through the clevis/spool from above with the cotter key inserted on the bottom side.

J-hook. A J hook is a lag screw with a curved h resembles a "J". (See Figure 130). You drive it into the pole like a lag screw and use it in conjunction with a wedge clamp.

Figure 130 – J-hook.

House Knob. House knobs, as shown in Figure 131, are small insulators either screwed in like a lag screw or clamped around a pipe. They are designed for smaller sized conductors because they cannot withstand the strain of large conductors.

Figure 131 – House knobs.

Wedge Clamp. A wedge clamp (see Figure 132) is a wedge-shaped piece of steel with a wedge shaped sliding sleeve that is placed on the ACSR conductor in a plex arrangement. The clamp tightens as strain is placed on it. It has a wire that fastens and unfastens to allow attachment to a spool insulator, J hook or other device. The wedge clamp is sized according to the size of the conductor, and is the quick, easy way to attach plex conductors.

Figure 132 – Wedge clamps.

7.16.4 Installation Procedures

The first step in installing a secondary service is to roll out the conductors. The secondary conductor comes on a wooden reel or coiled up. Place the conductor at the service pole (the load side), and roll it out to the utility pole (line side). Stretch the conductor across the ground from the service pole to approximately 5 feet. beyond the utility pole and then cut. It is important to have conductors of adequate length because splices are undesirable.

After cutting the conductors, attach the service drop to the support device at the service pole. Leave enough extra wire to make your connections. When the connection is secure, climb the utility pole and raise the service drop conductors on a handline. Sag secondary conductors by hand to achieve the proper clearance, and attach them to the attachment device. Again, leave enough conductor to make connections, and then cut off any excess wire.

Once you have properly sagged and secured the conductor at both ends, make the electrical connections. Before making any connections, ensure the customer’s service equipment is deenergized, and if possible also deenergize the transformer. This ensures that voltage is not provided to the customer until you have checked it. Make the load-side connections first, then the line-side connections.

To make the load-side connections, you must splice the service drop conductors to the customer’s service entrance cable. Use either compression connections or mechanical connections, and when the connection is complete, tape over the exposed connection and any exposed conductor. Tape the connections thoroughly to prevent shorts and grounds. It is not necessary to tape the neutral connection.

To make line side connections to the transformer, simply strip the insulation from the conductors and clamp them in the appropriate secondary bushings.

Once you complete the line side connections, energize the transformer. Before you turn on the customer’s service equipment, take voltage readings to make sure the output is the correct voltage and within allowable tolerances for the customer. Once you determine that the correct voltage is coming from the transformer, you can energize the customer’s service equipment.

7.17.0 Transformer Connections

We use transformers every day and don’t even realize the important role they play in our lives. In this section you will learn how to connect a single-phase transformer, including the factors to consider when making the primary and secondary connections.

Transformers step up or step down voltage to a usable level for the customer. As an example, the voltage coming into an installation is 69,000 volts, which is stepped down to 7200/12470 volts before being distributed throughout the base. Another transformer steps down the 7200/12470 voltage to 480/277 volts. This voltage is used for power and lights.

7.17.1 Basic Connection Considerations

7.17.1.1 Ground Connection

The first connection made to all transformers once they are in position is the equipment ground (sometimes called the case ground). (See Figure 133) Make this connection by installing a ground lug, then installing a piece of wire from the ground lug to the pole ground. You must attach the pole ground to a ground rod; a butt wrap cannot be used for an equipment ground.

Figure 133 – Ground connection.

7.17.1.2 Primary Connection

After safetly grounding the case, connect the primary. You will connect the primary in one of two ways, depending upon the distribution system voltage and how the high voltage rating of the transformer matches up. You will use either a line voltage connection or a phase voltage connection. (See Figures 7-134 and 7-135)

Figure 134 – Line connection.

Figure 135 – Phase connection.

Line Voltage Connection. Make the line voltage connection by connecting the H1 bushing to a phase and the H2 bushing to a different phase. This connection utilizes the system line voltage to power the primary winding of the transformer.

Phase Voltage Connection. Make the phase voltage connection by connecting the H1 bushing to a phase and the H2 bushing to the system neutral. This connection utilizes the system phase voltage to power the primary winding of the transformer.

7.17.1.3 Secondary Connections

Single phase pole mount distribution transformers have two identical secondary windings which can be connected in one of two ways. If the low voltage rating of the transformer is 120/240 volts, then each winding provides 120 volts. If you connect the windings in parallel, the transformer will provide only 120 volts (see Figure 136). If you connect the windings in series, you can still get 120 volts from one winding, but you can also get 240 volts by measuring across both windings (see Figure 137).

Figure 136 – Parallel connection.

Figure 137 – Series connection.

7.17.2 Three-Phase Connections

Industrial, commercial and institutional facilities use three- phase power. One way to provide this power is with a three phase transformer. Another way to provide three phase power is to “bank” three single phase transformers together. See Figure 138. Banking transformers involves hanging three transformers on a pole and making internal, primary and secondary connections to provide three-phase power to the customer.

Figure 138 – Bank of three transformers.

Just like the primary distribution system, three-phase secondaries can be either wye or delta. The needs of the customer will determine what kind of secondary

they need. Delta secondaries are used for heavy power loads (like factories), while wye secondaries are used when the load is evenly split between power and lights (like the schoolhouse). You can provide either a delta or a wye secondary, depending on how you make the internal and secondary connections on the transformer bank.

 

- To Table of Contents -


8.0.0 UNDERGROUND DISTRIBUTION SYSTEMS

8.1.0 Confined Space

8.1.1 Basic Facts about Confined Spaces

Confined Space is addressed in an Occupational Safety and Health Agency (OSHA) program that pertains to private industry and agencies throughout government. Since this program is very extensive, you should only be concerned with knowing the sections that directly affect you as an apprentice electrician and that the program’s standards require mandatory compliance. In particular you need to know that the most common confined spaces to which you will likely be exposed are manholes, trenches, crawl spaces, underground vaults, and hardened missile and communication silo complexes. Manholes are a key subsystem of any Underground distribution system.

8.1.2 Manholes

Manholes, by definition, are holes in the ground that allow entrance to utilities such as electrical, water, and sewer.

A confined space is an area that has the following three features:

  1. Is large enough to enter and perform work.
  2. Has limited or restricted means of entry or exit (something you can not easily get into or out of). For example: tanks, silos, trenches, manholes and crawl spaces.
  3. Is not designed for continuous employee occupancy (like an office or lab area).

Since manholes have these features, you are required by federal standards to follow certain procedures for safe entry.

8.1.3 Types of Entry

8.1.3.1 Permit Required

Confined spaces are classified as permit required or nonpermit required. A permit required confined space has one or more of the following characteristics:

Permit required spaces are those that have need of the following: entry supervisor, attendant, and entrant. All entry personnel must be trained in confined space entry, rescue procedures, and safe work practices. Workers must posses an entry permit that outlines the conditions of the space upon and during entry into the confined space.

The entry supervisor, normally the crew leader at the job site, has overall responsibility on the site. This supervisor ensure that personnel on the site are trained, that all safety equipment is available ready for use, and permit conditions are met.

The attendant must maintain communication with the entrants at all times. They are to remain outside the space and not attempt any rescue that involves entry until the rescue team has arrived. They are to make rescue attempts only by means of a lifeline prior to the rescue team’s arrival. If the attendant must leave for any reason, they are to order the entrants to exit the confined space. They also prevent unauthorized persons from entering the permit-required space.

The entrant must follow all safe work practices required by supervisory personnel. The entrant will wear a harness and be connected to the rescue equipment at all times. He or she must also notify the entry supervisor when hazards exist that have not been corrected and if they are taking any medication.

8.1.3.2 Non-Permit-Required Space

A non-permit-required confined space is a space that does not contain or, with respect to atmospheric hazards, have the potential to contain any hazards capable of causing death or serious physical harm. Most manholes fall into this category.

A non-permit-required confined space will be evaluated at least annually to ensure conditions have not changed to make it a permit-required space. A non-permit environment does not require permit, attendant, or site supervisor. The only requirement is to test the atmosphere prior to entry to verify that the work environment is a safe. It is an industry standard to have a minimum of two workers at the job site of a non-permit confined space.

8.1.4 Safety

8.1.4.1 Physical Hazards

Even if a confined space is classified as a non permit required space, the space may still contain other physical hazards, such as rodents, poisonous snakes, insects, slippery surfaces and deteriorated ladders.

8.1.4.2 Introducing Hazardous items onto Confined Spaces

Workers often intentionally or unintentionally introduce hazards into the confined space area. For example, some cleaners and heat sources used during the cable splicing process may create a hazardous condition within the confined space. Using a cigarette lighter as a light source or failing to redirect the exhaust fumes of work vehicles or gasoline powered manhole pumps or blowers can inadvertently introduce hazardous conditions. You must be constantly aware of the equipment and chemicals in your work area to avoid creating a hazardous confined space.

8.1.5 Test Manhole

8.1.5.1 Prepare Manhole Area

Knowing the procedures to test and prepare a manhole can help minimize the hazards associated with confined spaces. Because manholes are generally located in populated areas that are subject to pedestrian and vehicular traffic, you as well as the general public are subject to the hazards created by open manholes and the unavoidable presence of motor vehicles. These factors will obligate you to provide safe guards and perform preliminary actions prior to the work actually being performed. Examples of safe guards and preliminary actions are: set up traffic control equipment, remove manhole cover, and pump out water as required.

8.1.5.2 Setup Traffic Control Equipment

Several devices provide protection for personnel working in and around a manhole. Some of these are manhole guards, barricades, cones, and signs (see Figure 139.) If a manhole is in a vehicle traffic area, use cones to redirect the flow of traffic around the manhole and signs to control the flow of traffic. If the manhole is on a sidewalk, place barricades around the manhole to prevent people from falling into the open hole. These traffic-warning devices are of little value unless properly displayed.

Figure 139 – Barricades, cones, and signs.

8.1.5.3 Remove Manhole Cover

Manhole covers vary in weight depending on the type of manhole and its location. It is not uncommon for a manhole cover to weigh 200 to 350 pounds. Because of this, two people are required for safe removal and reinstallation. They lift the cover using manhole hooks and the leg muscles. They must never lift with their backs.

If snow, ice, or other conditions cause insecure footing around the manhole cover, clear the working area with a shovel or broom. Other options are to spread ashes, sand, or other suitable material around the cover to ensure firm footing. Your feet must be placed so they will be clear of the cover as it is removed. Since two people will be involved in the removal, good communications and coordinated action will be essential to the task at hand.

If the manhole cover is encased in ice do not strike it with a steel or iron tool. The striking of steel or iron against a steel cover may cause an explosion if the manhole contains a combustible gas. Use a hardened bronze cold chisel to remove the ice. The bronze cold chisel will not cause sparks when it strikes the manhole cover.

Do not use an open flame or salt to thaw ice around or over the cover. An open flame may also cause an explosion if a combustible gas is present in the manhole. A salt solution seeping into the manhole may contribute to cable and equipment corrosion. As a last note, never strike the center of a manhole cover to break it loose of ice; this may cause it to crack, especially in extremely cold climates.

You must wear personal protective equipment when working in a manhole. This equipment will include safety toed boots, gloves, and a hard hat. Use gloves to protect your hands as you grip the manhole cover hook and maneuver the cover out of the way. Safety toed boots protect your feet, and a hard hat protects your head while you are in the general work area and down inside the manhole.

8.1.5.4 Pump out Water as Required

In order to perform preliminary atmospheric detection testing or work in a manhole, you must first remove any water that may be present. Use powered water pump equipment to remove the water in a timely manner. There are two categories of water pumps, permanent and portable. Each will pump water out of a manhole, and each has its own particular area of use.

An example of a permanently installed water pump is the automatic sump pump. As the water level rises, a float closes a switch activating the pump. These pumps are not used in many manholes mainly for two reasons, cost and power supply. Installing pumps in every manhole would be very expensive, and most manholes are not equipped with available power. Manholes with an automatic sump pump generally contain critical components or equipment (i.e., transformers or load break elbows) supporting the underground distribution system and are entered often in support of maintenance on that equipment.

An example of a portable pump is the submersible pump, seen in Figure 140. This type of pump is brought to the job site by the worker. Some models require a 120 volt AC power source, while others run from a vehicle battery or hydraulic system. This type of pump can extract any amount of water that may be found within a manhole, however, if time is a factor it is not the pump of choice Since it can only pump a relatively small volume of water per minute. (All pumps are rated by gallons per minute).

Figure 140 – Submersible pump.

In cases where “time” is a factor a gasoline powered pump, seen in Figure 141, is better suited. This pump can remove large quantities of water in a short period of time. These pumps come in several different styles depending on the manufacturer. When you operate the pump, ensure the unit is located downwind from the manhole. This will prevent exhaust fumes from entering the manhole.

Figure 141 – Portable gasoline-powered pump.

The discharge line on all three types of pumps should be placed approximately 10 feet downhill from the manhole opening to prevent the water from running back into the hole.

8.1.6 Gas Detection

8.1.6.1 Description of Gas Detector

Before entering a manhole, always check the atmospheric conditions with a gas detector. The gas detector is a rechargeable, battery-powered instrument that uses three independent sensing elements operating simultaneously. Gas detectors are designed to detect combustible gases, toxic gases, and oxygen deficiency conditions. Most detectors have both audible and visual alarms. If the detector senses an unfavorable condition, a light will illuminate and a buzzer will sound.

8.1.6.2 Combustible Gases

Combustible or explosive gases are usually natural gas or hydrocarbon fuels. Two examples of hydrocarbon fuels are gasoline and jet fuel. These fuels are highly explosive; therefore, be careful when you encounter them in a manhole.

 

Warning

Do not smoke or bring open flames near a manhole. Use only approved lighting and heating equipment in a manhole since the making or breaking of an electrical circuit may cause an arc.

8.1.6.3 Toxic Gases

There are several toxic (poisonous) gases you may come in contact with while working in and around manholes. Some of the more common gases are carbon monoxide, hydrogen sulfide, and mangrove gas (swamp gas). These gases are very dangerous and in the case of hydrogen sulfide, respiratory paralysis may result within a matter of seconds.

8.1.6.4 Oxygen Deficiency

The normal amount of oxygen in the air is 20.8%. When the amount of oxygen is reduced to 12% or less, blood starvation begins and will cause death within one to three minutes. Sometimes, difficulty in breathing or a ringing sensation in the ears can be a sign of oxygen deficiency, but this does not always happen. For this reason, air in manholes containing less than 19.5% oxygen is considered dangerous and no one will enter the manhole until corrective action has been taken to correct the deficiency. Too much oxygen is also dangerous. The gas detector will detect that occurrence as well. A reading of more than 23.5% oxygen is considered a dangerous condition.

8.1.7 Inspect Gas Detector

It is very important you inspect the gas detector prior to each use. Make sure that you follow the inspection procedures outlined in the operation manual; your life may depend on it. During the inspection procedures, you are required to purge the detector prior to each use. This cleans off all contaminants from the sensors, ensuring that no faulty readings occur during calibration. Do this in a fresh air environment to prevent any contaminants from entering the meter during calibration.

8.1.7.1 Test Procedure

Once you have pumped the water out of the manhole and inspected the gas detector, you must test the manhole’s atmosphere using the following procedures.

Lower Meter and/or Hose. Since some gases are heavier than air; they still can be present at the top of the manhole while other types may be towards the bottom. For this reason you must take air sample readings at several levels by slowly lowering the meter or the meter’s hose towards the bottom of the manhole. Do not allow the meter or meter’s sample tube to contact the floor of the manhole as the gas detector could draw in dirt or water, obstructing the airflow to the meter.

If the test indicates it is safe to enter, you may climb into the manhole and check the corners and duct openings as well. If the non-permit confined space is determined safe, then you can remove the detector and put it away. However, it is highly recommended to leave the detector in the space during the entire time the space is occupied. In a permit-required space, the meter must remain in the space and continuously monitor the environment.

As stated previously, most detectors will have both audible and visual alarms. If one or both of them are activated during the initial test, you must ventilate the manhole to correct the deficient condition prior to entering.

Retest as Necessary. If the initial test proves the atmosphere is safe, you may enter the manhole and begin working. Conduct a retest of the atmosphere in any of the following situations:

Each installation will have its own local policy on how often you should retest the atmosphere. Know what the local policy is and retest the atmosphere accordingly.

8.1.8 Safety

It is important to always keep safety in mind while working in and around manholes. Manhole work can be fatal if you do not take the proper procedures. Always prepare the work area by setting up and using traffic control equipment. This will draw attention to the work site and prevent people from getting too close. Never, under any circumstances, enter a manhole without testing for both explosive and toxic gases and oxygen deficiency. Remember, testing manholes is done to ensure a safe environment. Do not forget prior to each use to test the gas detector to ensure it is functioning properly. Once you enter the manhole, it is recommended that you leave the detector on. Do not take hazardous materials into the manhole; this may create an unsafe work environment. Remember, a manhole can be a killer if you do not follow proper procedures and remain alert to the signs and symptoms that may be indicators of a serious atmospheric problem.

8.1.9 Ventilate a Manhole

8.1.9.1 Purpose of Ventilation

If the manhole atmosphere proves to be unsafe, you must ventilate the manhole. Ventilating procedures prevent or correct hazardous atmospheres in manholes by supplying fresh air. There are three methods of ventilation: forced air, natural, and sail.

Forced Air. This is the best method of ventilating a manhole. The forced air method uses a gasoline powered power blower (see Figure 142) to force fresh air into a manhole. Like the portable pumps that you learned about in an earlier course, power blowers are brought to the job site by the worker. A blower hose and/or manhole saddle are attached to the power blower and routed into the manhole, forcing in fresh air.

Figure 142 – Power blower.

Natural. The natural method is simply taking the manhole cover off of the manhole being worked and letting the air naturally circulate. This method of venting a manhole is the least effective. One reason this method is so ineffective is that a gas heavier than air could lie in the bottom of the manhole and not be forced to rise out.

Sail. The sail method uses the wind to ventilate a manhole. Use a piece of plywood or some other material for this method. Lift up the edge of the plywood facing the wind until the plywood forms about a 45 degree angle with the manhole opening. The wind is thus trapped and forced into the manhole, removing the bad air.

You can enhance the effectiveness of both the natural and sail methods by opening several adjacent manholes along the route of the manhole to be worked. This process works on the same principle as opening a window on one side of your house and then opening an outside door, creating a draft between the two points.

8.1.9.2 Procedures to Ventilate

8.1.9.2.1 Forced Air

Setup Equipment. Just like every other piece of equipment, you must first inspect the power blower and its accessories prior to use. If it is gas powered, check the oil and gas levels to ensure they are adequate. Place the power blower downwind from the manhole. This will prevent the exhaust fumes from entering the space being ventilated. Connect the hose to the blower and to the saddle. Lower the saddle into the manhole and secure it with the manhole cover.

Turn Unit On. Once the pre operation check and initial set up of the unit and accessories have been completed the blower can be started. Move the choke lever all the way over to the “on” position. Pull the pull rope to start the engine. Once the engine starts, slowly move the choke lever towards the “off “position while keeping the engine running. Allow the engine to warm up prior to applying any load.

Retest Requirements. Local installation policies and procedures will govern additional testing of non permit confined spaces. In addition to that guidance you must comply with the following requirements:

8.1.9.3 Safety

It is very important that you keep safety in mind at all times when working in and around manholes. The process of ventilating a manhole or other confined space is not hazardous in itself; however, failure to comply with required safe practices and retesting requirements could lead to catastrophic results. Wear ear protection if the situation warrants it. Open only as many manholes as you can provide adequate protection for.

Remember, you are responsible for protecting not only yourself and fellow team members, but also the general public. When off loading portable power equipment at the job site, ensure you have help. This equipment can be heavy and is often awkwardly designed. Use proper lifting procedures where required. Also, be aware of hot exhaust ports and never refuel gasoline powered equipment until it is allowed to cool.

Remember, do not permit anyone to introduce an open flame into or in the proximity of a manhole and ensure that any gas operated vehicle or equipment’s exhaust is kept downwind of the opening. It is your responsibility to ensure that these precautions are being met. The life you save may be your own!

8.2.0 Manhole Rescue

It is very important that you keep safety in mind at all times when working in and around manholes. The process of ventilating a manhole or other confined space is not hazardous in itself, however, failure to comply with required safe practices and retesting requirements could lead to catastrophic results. The wear of ear protection should be considered if the situation warrants it. Only open as many manholes as you can provide adequate protection for. Remember, you are responsible for not only protecting yourself and fellow team members, but also the general public.

When off loading portable power equipment at the job site, ensure you have help. This equipment can be heavy and is often awkwardly designed. Use proper lifting procedures where required. Also, be aware of hot exhaust ports and never refuel gasoline powered equipment until it is allowed to cool. Remember do not permit anyone to introduce an open flame into or the local proximity of a manhole and ensure that any gas operated vehicle or equipment’s exhaust is kept downwind of the opening. It is your responsibility to ensure that these precautions are being met. The life you save may be your own!

8.2.1 Perform Manhole Rescue

8.2.1.1 Equipment Requirements

Tripod. The tripod provides a firm anchoring point for the rescue winch (see Figure 143.) It is made mostly of lightweight aluminum and is easy to set up and transport. At the top of the tripod, on the underside, are two rings. These rings enable two rescue winches to be attached (if two people are working in the manhole) or a rescue winch and a pulley with rope to lower material into the manhole. The legs are extendable and should be fully extended prior to use.

Winch. The winch assembly has a retractable lanyard and is designed to act as a fall restraint (see Figure  143). The retractable lanyard gives individuals attached to it the ability to move around without having cable slack around their feet. As they climb down the ladder, the cable will pay out. As they climb up, the cable will retract. If a person were to fall climbing into the manhole, the fall restraint would activate, stopping the individual. A person using one of these devices must be wearing a full body harness. The rescue line is connected to the “D” ring of the harness.

Figure 143 – Tripod/winch assembly.

On the side of the unit is a handle to crank the individual up if a rescue is deemed necessary. Inspect the tripod and winch prior to set up at the job site. Inspect the tripod for cracks in the legs and make sure the nuts and bolts are tightened. Pull the cable out of the rescue winch and ensure it is good repair.

Rescue Rope. A manhole rescue requires two rescue ropes. Both should be at least 1/2 inch in diameter and as long as the depth of the manhole plus 15 feet.

8.2.2 Rescue Procedures

The Confined Space program provides specific guidance as to the who, what, where and when of manhole rescues based on the category of the confined space. While it will be important for you to be intimately familiar with the guidance once you are assigned to an operational unit, for now all that is important is that you know that you cannot attempt a rescue that involves entering a permit required confined space until a rescue team arrives.

The only rescue you are permitted to attempt is one that uses rescue equipment to which the victim is already connected by way of a lanyard and harness. There are many ways (dependent on available equipment) to perform a confined space rescue.

8.2.2.1 Evaluate Situation

Before ever attempting a rescue, you must first determine if a rescue is even warranted. Take note of the worker’s position and call to him or her to see if you get a response.

Call out a second time if you do not get a response from the first inquiry. The worker may be preoccupied with work or cannot hear you due to a high noise level from outside. If you get no response then consider a rescue. Check to see what position the victim’s body is in with respect to any hardware or equipment that may hinder the rescue. Try to detect what might have caused the victim to lose consciousness. Do this by using your sense of sight, smell and taste. Is there evidence of fire, smoke or an acrid taste to the air? Anyone of these conditions are good indicators that the victim may have been electrocuted. Keep your surroundings in mind and know what you’re going to do prior to committing yourself. In a non-permit required confined space rescue be prepared to get in and out with the victim as soon as possible.

8.2.2.2 Provide for Personal Protection

This “step” should be happening throughout the entire process. A rescuer’s personal safety is of primary importance. If the rescuer is injured, nobody will be saved. The first thing you do is wrap a rescue rope twice around your chest and secure it with 3 half hitches. This is your rescue you if you should be overcome by whatever affected your victim.

Use caution when entering the manhole. Make sure you remain conscious of your surroundings. Don't get caught up in the rescue rope. To ensure you do not become electrocuted, attempt to turn off suspected energized circuits or physically isolate the circuit either by moving it or moving the victim from it prior to attempting the rescue. Don personal protective rubber equipment. If the victim appears to have been overcome by dangerous gases, and you have help, turn on a power blower to ventilate the space during your rescue attempt.

8.2.2.3 Call for Help

If the victim did not respond to you and you feel a rescue is necessary, call for help prior to entering the confined space. You are not an expert in rescue or medical care, even if you have received some training in these areas. It is always better to call the experts to the job site. In today’s military most electrical work centers have radios installed in their trucks and/or have hand held radios for you to use at the job site. These radios give you ready access to contact emergency personnel if the need ever arises. If no radio is available, send a runner to the nearest phone or do whatever is necessary to get help.

8.2.2.4 Raise Victim out of Manhole

Using pre attached rescue equipment (i.e., Tripod/Winch assembly, Windlass crank), or rescue ropes, raise the victim out of the manhole using the applicable procedures:

  1. Rescue lanyard and harness equipment already attached to victim. (Tripod/Winch)
  1. Rescue rope to be tied onto victim.

8.2.3 Safety

In addition to hazardous gases and oxygen levels, there are certain other hazards that you need to be aware of so that you can exercise proper ground safety practices in order to avoid accidents.

8.3.0 Underground Duct Systems

Underground distribution systems provide the highest degree of reliability, protection, and ease of maintenance of any type of system construction. These advantages are derived through the use of duct systems and manholes. An added benefit of underground duct systems is that the general public sees it as a way of improving the appearance of their surroundings. Because of this, most newly constructed power distribution systems supporting population centers are now installed underground. As an electrician who will be pulling stand-by duty, you will want to ensure that your efforts toward the installation of a duct system are of the highest standards. If you do otherwise, you may find yourself being called out to make repairs during the worst of times.

8.3.1 Install Duct System

Duct systems provide a means to distribute power to the customer while enabling you to install, access and repair the power cables with relative ease. This type of system provides better protection of power cables than Overhead or Direct burial systems. It is much more expensive to install; however, the benefits far outweigh the cost.

8.3.1.1 Manholes

A manhole is a chamber in the underground duct system, large enough for personnel to enter, to and from which cable is pulled. (See Figure 144) The manhole's main purpose is to allow access for splicing and testing of underground cables.

Figure 144 – Manhole.

Manufacturers generally construct pre-cast manholes of concrete at the factory and truck them to the site where they will be installed in the ground. These manholes must provide the same inside dimensions, strength, and sealed joints as the monolithic (made of one piece) cast-in-place manholes constructed of reinforced concrete or brick. No matter what type of construction method is used manhole sizes will not be less than 4 feet wide, 6 feet long, and 6 feet deep. The access opening to the surface must be at least 32 inches in diameter. The shape and size of the manhole depends on the number and size of ducts and the directions in which they leave the manhole.

Spacing. To limit the stresses placed on power cable being pulled through the ductwork of a manhole, engineers have determined that the following maximum distances must be observed. These maximum distances limit the pulling tensions to acceptable values for installation of common types and sizes of cable.

Note

A riser (see Figure 145) is used on utility poles to transition the cable from the ductwork to a surface device (transformer, capacitor bank or switch) installed on the pole. The cable will be run from the manhole to the riser where a 90 degree sweep is used to make the one and only authorized change of cable direction permitted when transitioning an underground cable to an overhead connection.

Figure 145 – Riser.

Installation. The area used for manhole installation must be clear of gas lines, water mains, and other utilities. Use a backhoe to dig the opening for the manhole. The bottom of the hole should be level compacted soil without any large rocks or obstructions that could prevent the manhole from settling properly.

A crane is often used to lift the manhole from the trailer and place it in the hole. Ducts are installed prior to backfilling around the manhole. The area around the manhole must be backfilled and compacted with sand or excavated material that is fine and dry. A manhole neck is used to extend the manhole opening to the finished grade.

8.3.1.2 Ducts

In the simplest of terms ducts are hollow tubes commonly called conduit. A section of conduit is placed together with other conduits to form an underground duct system. The underground cables are pulled into the ducts between manholes. The duct system provides maximum protection for the cable and allows easy maintenance of the system

Construction. Ducts can be made out of fiber, plastic (PVC-polyvinyl chloride), metal, concrete, tile, or composite materials; however, you will most commonly will work with PVC (polyvinyl chloride) or metal. The size of the duct depends on the size of cable(s) being installed. The duct diameter should be at least 1/2 inch to 3/4 inch larger than the cables installed. Four inch ducts are normally used in Underground distribution systems.

Duct runs should be as short and straight as possible. Bends should be laid out on the greatest possible radius to avoid sharp curves. The run should also be slightly sloped toward one or both manholes to allow water drainage from the ducts and into the manholes. The slope should be 4 inches for every 100 feet of duct length (see Figure  146).

Figure 146 – Duct slope.

Configuration. Ducts, as shown in Figure 147, are arranged in the manhole in various ways. The number of ducts in a run depends on the ducts required and the number of spare ducts needed for future growth. This number may vary from two to the recommended maximum of nine ducts in the run.

Figure 147 – Duct.

 

Note

Experience has proven that installing just the exact number of ducts needed has not been favorable in the long run. In order to accommodate future load growth, the established practice is to install at least 25% more duct work than what has been planned for use at the time of initial installation. For example, if the plan calls for four ducts to be used, you would install at least one extra duct run for future growth.

The distance between ducts should be at least 2 inches. The cables installed in these ducts will generate a small amount of heat that will ultimately affect the current carrying capability of those cables. The space between the ducts will help dissipate the heat. If the ducts are to be encased in concrete, at least 3 inches of concrete should be placed around the outside as well.

Installation. As a general rule, install ducts where they will cause the least amount of disturbance. Do not run a duct system through the middle of a parking lot when you can go around it. This is to avoid subjecting the duct system to the weight of vehicles as well as having to dig up pavement during the installation and possibly when repairs are required.

Avoid crossing over or under other utilities i.e., water, sewer, and communications, as much as possible. If you have to cross them, you must follow strict separation standards. Avoid placing duct runs through muddy, shifting, or corrosive soils when possible. If there is no option, construct the duct runs in such a manner as to minimize movement and direct exposure to corrosion. This will usually entail encasing the duct work in concrete.

Ducts which run near roadways should be installed parallel to the road and under the shoulder to limit the possibility of damage by traffic. If they are run parallel under the road, ducts should travel under only one lane of traffic.

Specific procedures to install duct are as follows: Begin by laying the duct midway between two manholes and work toward the manholes. Install the ducts in spacers (see Figure 148) placed at no more than 5 foot intervals along the run. These spacers will provide the minimum 2 inches between ducts and 3 inches between the duct and the bottom of trench required to dissipate the heat from cables placed in the duct work. If the duct work is to be encased in concrete, the concrete should extend 3 inches on top, bottom and to the sides of the ducts supported by the spacers.

Figure 148 – Duct spacers.

Plastic (PVC) ducts are joined together with a driven sleeve (coupling). Usually the driven sleeve is manufactured onto one end, which is commonly referred to as the bell-end. PVC conduit can be cut to the required lengths using any coarse-toothed saw. The PVC is then cleaned of all dirt or other contaminates prior to joining. Once assured that the PVC is clean the pieces are joined together using PVC cement to ensure a watertight seal.

Metal ducts are joined with a scre-on coupling. Pipe wrenches are used to tighten the ducts to the coupling to give it mechanical stability. No sealant is required.

8.3.1.3 Cable Racks

Cable racks are attached to the walls of a manhole and are made of galvanized metal with insulating porcelain saddles.

Cable racks are used to support high voltage cable within a manhole. They enable the cable to be secured off of the floor and out of the way of personnel entering and exiting the manhole. Besides protecting the cable and its splices from accidental damaged by inadvertent contact, cable racks also provide for placement of the cables within the manhole in a neat and organized fashion, enhancing the ability to perform maintenance and troubleshooting actions.

Spacing. Cable racks should be positioned so that every splice rests between two racks. There must be at least six inches of cable between the edge of the splice and the porcelain saddle on which the cable rests. Rack spacing will normally be about 3 to 4.5 feet apart for electric power cables. Actual spacing depends on the size of the cable and its maximum bend radius. At least two racks should be located on each wall except where that would interfere with duct entrances.

8.3.1.4 Advantages and Disadvantages of Duct Systems

Advantages. Underground duct systems provide increased electrical service reliability, and greater physical protection compared to Overhead and Direct burial cable systems. In addition, they allow for ready access by electricians for testing, repair, and replacement of cables, system equipment, and components.

Disadvantages. The disadvantages of underground duct systems are few. The biggest drawback is that the initial cost of installing one is significantly higher than the other two types of construction. Of lesser concern is that manholes are restrictive in terms of work area and may contain dangerous gases, insects, reptiles, and water.

8.3.2 Safety

Installation of an underground duct system will pose a whole new array of safety related hazards not previously discussed. Where there are excavations, as is the case when installing manholes and digging lengthy trenches, there will usually be heavy construction equipment. This equipment is dangerous not only to operate, but also to work around. The large areas of ground that will be opened up will require barricading to make unauthorized people are made aware of the hazardous construction area and keep them out. Holes and trenches dug deeper than they are wide and capable of engulfing the personnel working in them will be classified as confined spaces and require compliance with a host of new safety related standards, such as shoring up the sides of the trench and holes.

The use of proper lifting procedures when moving ducts and having enough workers on site will be especially important to any safe installation project. Projects are usually accomplished in phases and build off of existing systems, so it is important that no one let their guard down and become complacent. Check the manholes, even if they are newly installed, for dangerous gases before entering. Wear personal safety equipment and goggles while drilling holes in concrete to mount cable racks and while operating other powered equipment.

8.4.0 Buried Cable

New cable technology and improved methods of installation are responsible for the growing trend toward direct burial cable systems. Direct burial means the cable is buried directly in the ground and covered with earth. This type of installation gives satisfactory service where only a relatively few buildings or load centers are involved and a suitable cable route is available.

8.4.1 Basic Concepts of Direct Buried Systems

8.4.1.1 Trenches

A trench is a long narrow cut in the ground with steep sides. The trench is the key feature that characterizes the direct burial system. Because of this the trench warrants further discussion. A trench can be a permit required confined space if it meets established criteria under OSHA’s Confined Space program. You do not need to know the specific criteria, but what is important for you to know is that trenches cannot be taken for granted. A key characteristic that classifies trenches as a permit required confined space is that they contain a material, dirt that has the potential of engulfing the entrant. Because a trench can easily cave-in causing the “entrant” to become engulfed, you must always maintain an awareness of your as well as your co-workers’ position when working Direct burial installation projects.

Trenches are dug using construction equipment or by hand. The method of excavation will depend on a number of factors such as the availability of equipment, length of run, and proposed route of the trench.

A trench’s depth is also based on a number of factors; however, all will meet the minimum depths listed below. These depths are based on the amount of voltage the cable will be carrying.

Other factors that may require you to bury cables deeper are extremes in temperature or wet areas. In extremely frigid locations such as the Arctic and Antarctic, a condition known as permafrost exists. Permafrost is a permanently frozen layer of ground that is comparable in hardness to concrete. Under these conditions, cables will need to be buried more deeply than previously mentioned.

In extremely cold areas the earth is subject to freezing, and it will be important to bury the cable below the frost line to avoid damage by the expansion and contraction of the earth during freezing and thawing. The frost line is the depth in the soil where the earth is not subject to freezing. In areas that are extremely wet, cables may need to be buried more deeply then previously mentioned to keep them from “floating” to the surface.

8.4.1.2 Ground-level Equipment

Laying cable in a trench is just part of the installation of a Direct burial system. The ultimate reason for installing cables is to supply power to a piece of equipment that will supply power to the customer. At the end of Direct burial trenches, there will need to be a transformer, switch, or some other piece of equipment to serve the end purpose.

Pad-mounted Transformers. Pad mounted transformers, as shown in Figure 149, are used to change the primary voltage to a secondary voltage. In a Direct burial system, these transformers are generally placed on pads, hence the name pad mounted transformer. These pads are normally made of concrete, but are sometimes constructed using other types of material such as plastic.

Figure 149 – Pad-mount transformer.

Enclosures. An enclosure is another type of pad-mounted equipment (see Figure 150). It can house a wide variety of electrical components, such as switches, cable terminations, and even pole type transformers.

Figure 150 – Enclosure.

8.4.1.3 Power Cables

The cables you are burying to distribute electricity around the base fall into two categories, depending on the voltage they carry.

Feeder. The high voltage cable run from the substation to the transformer is known as the feeder. It will supply power to the general areas requiring it. The transformer and secondary circuits will further distribute the power to the customer.

Lateral. Service laterals are the buried service conductors from a transformer to the first point of connection on a building. The service lateral is similar to the service drop you learned in the Overhead block of instruction. The only real difference is that the conductors are installed directly in the ground rather than being supported in the air.

A service lateral can come from a pad mount transformer, an enclosure, or down a riser from a pole-mount transformer. Service laterals can be installed in a duct or directly buried. The procedures for the installation of service laterals are the same as for Direct burial cable. Refer to Figure 151 to see an example of what a service lateral coming from a pad mount transformer looks like.

Figure 151 – Service lateral example.

8.4.1.4 Advantages and Disadvantages of Duct Systems

Advantages. There are a few advantages to a direct burial system. It is cheaper to install than an underground duct system, yet affords a good amount of protection from storm damage. It also has lower maintenance cost than an overhead system. Like the underground duct system, it is also aesthetically appealing. Since the cables are thermally insulated by the earth, their year-round temperature only varies by a few degrees, which extends the useful life of the cable.

Disadvantages. The disadvantages of a Direct burial system are that the cables, no matter how well designed, are susceptible to damage from all conditions that may exist in the soil such as corrosion, water leakage, and shifting of the ground. These cables are also easily damaged when subjected to compressive forces and digging operations. In addition to the physical susceptibilities, direct burial systems are difficult to troubleshoot and maintain (no access to cable except for termination points) and replacing a damaged cable is nearly impossible.

8.4.2 Installing Direct Burial System

Installing a Direct burial system is a fairly simple process and requires less effort and expense than the underground duct system. The steps are: dig the trench, install the bedding material, cable, and cable marker tape, then back fill and, finally, install cable route markers.

8.4.2.1 Excavate Trench

As stated earlier, trenches can be dug either by hand or using heavy equipment. Two of the most common types of excavating equipment are trenchers and backhoes.

The backhoe, as seen in Figure 152, is used for wide trenches or when no other equipment is available. Buckets of different widths can be used depending on the desired width of the trench.

Figure 152 – Backhoe.

The trencher is the preferred equipment with which to install a Direct burial system (see Figure 153). They are available in a variety of sizes and models and are specifically designed with the task of excavation in mind. Trenchers used to support military requirements are capable of digging trenches of various widths, usually ranging from 8 inches to 24 inches and depths of as much as 84 inches depending upon the type of trencher used. Trenchers can also be equipped with a hydraulically controlled dozer blade for back filling operations. The cable plow, shown in Figure 154, is a type of trencher ideally suited for wide open unobstructed trenching operations. Most cable plows open the trench, lay the cables, and cover the cables all in one operation. Cable plows will offer the distinct advantage of saving time and money and minimizing the disturbance to an area.

Figure 153 – Trencher.


Figure 154 – Cable plow.

8.4.2.2. Install Bedding Material

The trench must be free of rocks or sharp objects that might damage the cable. If the ground is rocky or you suspect that the ground could damage the cable, use a cushion of sand. The most common practice is to trench 3 inches deeper than the required cable depth and place 3 inches of sand in the bottom of the trench before installing the cables.

In areas where vehicular traffic is likely (roads, driveways, etc.), the cable must be protected, at a minimum, with rigid conduit. Conduit protects the cable from the compression forces of the vehicles and makes replacement easier. An additional benefit of placing the cable in conduit is that there will be no need to replace pavement that would otherwise have been removed had re-trenching been required.

8.4.2.3 Install Cable

The cable is placed in the trench as soon as possible either during (as in the case of a cable plow) or immediately after the trenching operation. All cable placement will be done under constant supervision to be certain that no damage to the cable occurs during the laying operation. Clear all tools and equipment not needed for this process from the trench area. Whenever possible, pay out the cable from a reel mounted on a moving vehicle or trailer. Support the cable reel so that it can be turned easily without placing undue strain on the cable. Place the cable carefully in the trench by hand. Lay the cable in the trench with some slack in it, since a tightly stretched cable is likely to be damaged as back fill material is added, and the slack will allow the cable to expand and contract during extreme temperature changes. Do not drag the cable should over sharp edges of the pay-off equipment, parking lots, roadways, or anything else that may damage it.

8.4.2.4. Install Marking Tape

Cable marking tape serves as a warning that there are energized high voltage cables buried below. It is generally a roll of brightly-colored plastic tape about two inches wide, usually marked with the words “CAUTION – ELECTRIC CABLE BELOW” or some similar statement. See Figure 155. This cable marking tape will let future excavators know there is an electrical line below. It must be placed at least 12 inches above the cable it protects for the entire length of the cable run and is unrolled into the trench midway through the back filling process.

Figure 155 – Marking tape.

8.4.2.5 Back Fill using Suitable Material

If sand is protecting the cable, add an additional 6 inches of it on top of the cables after they are installed to further protect them from the back fill material. When you back fill the trench, it should be as free of rocks as possible so as not to cut or damage the cable during tamping operations and as the ground settles. Tamp the back fill material well to keep the trench from settling when it rains. Remember to install the cable marking tape at the appropriate time during the back filling process.

8.4.2.6 Install Cable Route Markers

The primary purpose of cable route markers is to identify the location of buried cable and any splices that have been made in it. Markers are available in different styles and made of different materials. Most of them provide the capability to stamp identification information such as the circuit/splice ID number, size and type of cable etc. You will use these markers to locate circuits requiring repair or maintenance on associated system components.

Cable markers must be placed every 200 feet or anywhere a cable changes direction.

They are also required at every splice in the direct burial system. The markers are to be installed 2 feet from the right side of the trench being marked as you look toward the circuit's supply point (line side). When cables are used in lighting circuits and if the lighting poles show the direction and change in the system, cable markers are not required.

8.4.3 Protection Options

8.4.3.1 Above Finished Grade

Direct buried cables emerging from the ground shall be protected by an enclosure or rigid conduit extending at least 8 feet above the finished grade (see Figure 156). This is required to protect them from physical damage caused by lawn mowers or vehicular traffic and to prevent personnel from coming in direct contact with the cables.

Figure 156 – Riser.

8.4.3.2 Below Finished Grade

Protection shall extend below grade a minimum of 18 inches. Generally, the cable is run through a riser to protect it as it enters and exits the ground.

8.4.4 Safety

Keep these safety items in mind as you install direct buried cables:

Determine whether the trench is considered a confined space or not. If you have any doubts, ask your supervisor about it. If it is, you will need to process a confined space permit and shore the trench walls prior to entry.

8.5.0 Underground Cable

Today, more and more distribution systems are being built underground to leave the area looking as natural and undisturbed as possible. These systems perform in different environments and the materials from which they are constructed must be adapted.

Unlike overhead construction, underground distribution systems use cable to distribute power from the substation to the customer, and more than one cable can be installed at the same time. As an CE, it is important you keep this in mind. This economy of effort will serve you well should you ever have to repair cable or cables within an underground duct system.

8.5.1 Install Cable in a Duct

8.5.1.1 Rigging Set Up

Rigging set up refers to the actions required to pre position equipment used to physically pull cable through the ducts into the manholes.

Pulley Diameter. During the cable pulling process, you will be running the cables over several pulleys. If the diameter of the pulley is too small, the cable will bend too sharply, resulting in damage to the internal layers of the cable. Depending on manufacturer specifications and the reference you use, the minimum bending radius may vary.

As a general rule, the minimum bending radius of primary cable is 12 times the overall diameter of the cable. This means if your cable has a diameter of 1inch, the minimum size pulley you could use while pulling cable would have a diameter of 24 inches, with a radius of 12 inches. As a rule, the minimum bending radius for secondary cable is 6 times the diameter of the cable.

Pulley Position. Pulley position is the most important part of rigging. Proper placement will prevent damage to the cable while it is being pulled into the duct. If you are pulling cable into a manhole, adjust the pulleys to keep the cable from scraping against the top or bottom of the duct opening. Also, place them to prevent the cable from coming in contact with the manhole opening.

If you are pulling cable into or out of an enclosure, position the pulleys to keep the cable from rubbing on the duct openings as well as the enclosure.

When it comes to pulley positioning, keep in mind that you want to prevent the cable from rubbing on anything so neither the cable nor the equipment is damaged. There are several different types of pulleys available, each having its’ own purpose.

Anchoring.Anchoring the pulley is important as well. You must use chain or rope capable of handling the tension of the pulling operation. Manholes will have a “pulling-in iron” (also referred to as a pulling eye) constructed into the wall of the manhole (see Figure 157). Its sole purpose is to provide an anchoring point to attach pulleys.

Figure 157 – Pulling-in iron.

If you are pulling into an enclosure, you may use the boom of the line truck as one of your anchoring points. Positioning the boom over the duct opening and hanging a pulley from the winch line may be all you need to prevent the cable from rubbing on the duct opening and/or enclosure.

There is more than one way to position and anchor pulleys when pulling cable. The manhole or enclosure’s configuration and size may be different every time. Check out your surroundings and find the best scenario to position and anchor your pulleys.

8.5.1.2 Installation Procedures

Select the Duct.

Before pulling cable, you must determine which duct or ducts are going to be used. For the most part this information will be provided to you on prepared blueprints or drawings. If no blueprints or drawings are available, then you will be required to make a decision based on established practices used in the career field.

Blueprints/drawings. During the planning phase, an electrical engineer will assign the ducts to use. The electrical engineer will make this clear using blueprints or drawings that will be included in the work order package. Your responsibility is simply to install the cable or cables through the ducts and manholes he or she has designated. Experience has shown that because of the long periods of time that elapse between envisioned projects and their actual installation, changes to the initial planned drawings are sometimes required. If this situation arises, you will have the responsibility of proposing recommended changes to the engineer based on established practices.

Location of Cables. Select the duct to be occupied throughout the entire length of the proposed run while maintaining the same relative position in the duct bank throughout all manholes where possible. When selecting the duct for any particular cable, do not assign a duct whose occupancy of cables may block other vacant ducts or block a racking position. Try to select a duct that will allow the heat that is generated to dissipate.

Typically, the outer ducts in the duct configuration are the coolest and are generally reserved for high voltage cables while the inner center ducts are filled with low voltage and control cables.

Try to place longer cable runs in the bottom ducts and shorter cable runs in the upper ducts. This is possible if you are running several cable runs during the same job. If not, use the lower ducts first and then work upwards so you use the upper ducts last. This prevents you from having to install cables under an existing run at a later date.

Prepare Cable and Duct for Installation. Once you have selected the duct into which you will be pulling cable, you are ready to prepare the duct and cable for installation.

Test Cable. It is always best to test a cable prior to its installation, since installing a faulty cable is obviously a waste of valuable time. All cable should receive an initial acceptance test, using a DC high potential test set when it first arrives from the manufacturer. Since cable may be sitting around in a storage yard or warehouse for years before it is needed, you will conduct a second test for cable faults, using a megohmmeter (megger), prior to transporting the cable reel from the storage area.

Rodding the Duct. Before you can install cables, you need to check the duct system for structural integrity and then clean it as necessary. This is done through a process called rodding. Rodding is accomplished by inserting a number of short, jointed wooden rods or a flexible fiberglass or steel rod into the duct starting at one manhole and going to the next. Two types of wooden duct rods that you may encounter are the screw and quick-coupling.

Both types generally come in 3 or 4 foot long sections and are approximately 1 inch in diameter. They fasten together, as their names imply; screw type rods are connected by screwing one section into the next, while quick-coupling rods use an interlocking joint to join one rod to the next. The actual process of rodding is accomplished by linking one rod to the next, inserting them into the duct, assembling more rods, pushing the joined rods farther into the duct until the first rod appears at the distant manhole. While you may encounter wooden duct rods, the most common duct rod used today is a continuous piece made of fiberglass or steel as shown in Figure 158. It is inserted into the duct and pushed the entire length of the run.

Figure 158 – Fiberglass rod.

Rodding is done from one end of the conduit run to the other and not from both ends to the middle. If the conduit run is on a slope, rodding operations should proceed from the top toward the bottom of the slope (let gravity help you). If you encounter an obstruction, you can use various leaders to try to dislodge it. If you run into problems, report them to your supervisor

Once you have pushed the rod through the entire length of the run, attach the “cleaning” rope and pull it back through the duct. This rope will then pull in a heavier pull rope. Cleaning mandrels can be attached between these ropes, cleaning the duct as you pull in the pull rope.

Cleaning mandrels are used to clear obstructions from the duct that may damage the cable during the pulling process.

They come in different types depending on the application (large objects, small pieces of concrete, dirt). Figure 159 shows two different types of cleaning mandrels. Figure 160 shows one way a mandrel is connected for use. In some cases, the pull rope will be pulled in using the duct rod and not the “cleaning” rope. If you use this method, attach one side of the mandrel to the pull rope and the other end to the cable to be installed. In either situation, the duct requires cleaning prior to cable installation.

Figure 159 – Flexible steel and wire brush cleaning mandrels.


Figure 160 – Cleaning mandrel being pulled through duct.

The duct cleaning process includes the following steps:

  1. Use the duct rod to pull in the pull rope.
  2. Attach a cleaning mandrel between the pull rope and the cable to be installed.
  3. Pull the cable into the duct.
  4. As the cable is being pulled in, the duct is being cleaned at the same time.

Prepare Manholes. After you have tested the cable, cleaned the duct, and installed a pull in rope through the duct, you are ready to rig the pulling-in manhole with pulling apparatus. There are two methods in which you can install cable and each method is dependent on the type of pulling apparatus to be used. One method uses a pulling frame (Figure 161) and the other a pulling-in sheave (Figure 162) and manhole sheave (Figure 163).

 

Note

If a manhole contains pulling in irons, either type of equipment may be used. However, if no pulling in irons are present, only the pulling frame can be used.

Figure 161 – Pulling frame.


Figure 162 – Pulling sheave.


Figure 163 – Manhole sheave.

Set Up Cable Pulling Apparatus. The pulling frame consists of a pulley near the top and one near the bottom to guide the cable. Set up of this equipment entails adjusting the height of the two pulleys to prevent the cable from rubbing on the duct and/or manhole openings as it is being pulled in.

Adjustments are required at each and every manhole in which the pulling frame will be installed, since the depths and the height of ducts are subject to change depending on the type and size of the manholes.

The other method of cable installation requires the use of a pulling sheave and a manhole sheave. In order to rig a manhole using this method, attach the pulling sheave to a pulling-in iron in the manhole and install the manhole sheave over the manhole collar. The pulling sheave is anchored by a chain or heavy-duty rope to the pulling-in iron embedded into the wall of the manhole. You will need to make adjustments to the length of the chain or rope in order to position the bottom of the pulling sheave so that it is in line with the duct into which the cable will be pulled.

The manhole sheave consists of one or more pulleys and just fits over the manhole collar. Its purpose is to prevent the cable from rubbing on the manhole collar as it is being pulled out of the manhole towards the line truck. There is no adjustment for the manhole sheave.

No matter what method of installation you use, be sure to check all equipment for proper alignment and operation before actually beginning the cable pull. Failure to do so will more likely than not result in damage to the equipment or cable and possibly injury to you or your co-workers.

Placing Cable Reel, The cable reel may be set on a trailer or on cable jacks as shown in Figure 164. Regardless of the method used, the reel has to be set up at the feeding manhole on the same side of the manhole as the duct run in which the cable will be installed.

Figure 164 – Feeding manhole using cable jacks.

The cable will be payed out carefully from the top of the reel. If you are using cable reel jacks, inspect them prior to use to ensure they operate correctly and are clean, lubricated as required, and capable of supporting the required cable reel. The stand will support a lot of weight, so it is important that they work properly during the pulling process.

Never pay out the cable from the bottom of the reel since this will put a reverse bend on the cable, causing interior damage to the cable components. This affects the way that the layers seat, causing air pockets that could lead to cable failure. If the duct run contains a curve, set up the cable reel at the manhole nearest the curve. Pulling through the curve first will make for an easier pull. If you use cable reel jacks, ensure they are set on a firm, level surface to prevent them from sinking into the soil or falling over.

Rig Feeding Manhole. The first thing you do when rigging the feeding manhole is to set up the cable guide and the cable lubricator if one is used. The cable guide is a flexible metal tube that protects the cable as it is pulled into the duct (see Figure 165). Cable guides come in different sizes depending on the size if the duct. The nozzle (the end that will be placed inside the manhole) slips into the duct opening. The cable enters the cable guide through the funnel at the top.

Figure 165 – Cable guide.

Cable lubricators are sometime used in cable pulling operations. Their use depends on a number of factors such as the size of the cable to be pulled, number of cables already in the duct being pulled into, the length of the duct run, and the number of bends or angle of bends expected to be encountered. If you use a cable lubricator, the cable will feed through it and the cable guide before entering the duct.

The lubricator is used to coat the cable sheath with a lubricant that helps the cable slide through the duct. Special cable lubricant is put into the lubricator. As the cable is pulled, it will draw some of the lubricant into the duct with it. The lubricant should be applied very liberally. The average amount of lubrication is 6 to 8 pounds per 100 feet of one 3 inch diameter cable or three 1inch diameter cables.

Install Cable. Once you have installed the pulling-in apparatus and positioned the cable reel, the cable is ready for installation. Prior to actually pulling in the cable three final actions are required. They are sealing of the end of the cable that is being pulled, attaching the pull rope or winch line, and setting up the line truck.

Clean and Seal Cable Ends. You must seal the cable ends to prevent moisture and dirt from entering the cable while you pull it through the duct. If moisture or dirt is allowed to enter the cable during the pulling process, cable failure may occur and cause you to repeat the entire cable-pulling process. Attention to small details such as this can prevent unnecessary damage to cable and save you a lot of time in re-accomplishing the job.

Attach Pulling Rope/Winch Line to Cable. After sealing the cable end, attach the pull rope or winch line to the end of the cable using a basket grip (see Figure 166). Slide the basket grip is slid over the cable end to use as the attachment point for the rope or winch line. If the basket grip does not have a swivel manufactured into it, placer one between the grip and the pull rope or winch line. This swivel will prevent the cable, pull rope or winch line from twisting as you pull in the cable.

Figure 166 – Basket grips.

When installing or removing basket grips, be alert for broken strands as they become worn with use.

After attaching the pull rope, place a marker on it approximately 20 feet ahead of the cable to alert personnel at the pulling end that the cable is nearing the manhole entrance. This marker could be something as simple as electrical tape wrapped around the pulling rope or winch line.

Use Line Truck to Pull Cable. The capstan on the line truck is normally used when pulling cable into a duct using a pull rope; otherwise the bed winch is used. The speed at which the cable is drawn into the duct will vary and be dependent on such factors as the number and the size of the cables, the length of the pull, and curves in the duct. It is always a good practice to begin the pull slowly and adjust the speed from there.

The average cable pulling speed is 40 feet of cable per minute for a single cable and 20 feet of cable per minute for two or more cables. Pulling speeds below 20 feet per minute are considered to be low, while speeds above 60 feet of cable per minute are considered to be high speeds. Avoid pulling at high speeds as much as possible due to the difficulty in properly lubricating and inspecting the cable as it comes off of the reel.

Once the 20 foot advance marker appears in the pulling manhole, reduce the pulling speed significantly. You will need to pay close attention at this point in the pull to ensure that the cable continues to roll unobstructed over the pulleys. For safety purposes, no one should be inside the pulling manhole during any part of the pulling-in operation and everyone needs to stay clear of the pulling rope or winch line while it is under tension.

Ropes and winch lines can break while under strain, whip out, and cause serious injury to anyone in the wrong place at the wrong time.

Cable Slack. Once the cable comes out of the duct opening, it will follow the contour of the manhole wall and be placed on the cable racks. Additional cable must be pulled to allow for splicing, testing, removal of damaged ends, and proper racking. The length of cable required in each manhole depends on the size of the manhole and whether the cable will be spliced or not. As a general rule, the length of excess cable required for splicing and testing usually amounts to 1 1/2 feet per cable or 3 feet per section. Specific lengths should be recorded on the blueprint or drawing of the cable being installed.

Remove Damaged Ends. During the pulling process, the cable ends are sometimes damaged. If this occurs, remove the ends prior to racking and splicing. Remove the basket grip and cut the damaged cable ends off with cable cutters. Once you have cut the cable ends you must seal them to prevent moisture and dirt from entering the cable while it is waiting to be spliced or terminated.

You should perform an insulation resistance and continuity test on the cable immediately after installing it. These tests will enable you to determine if the cable has sustained any damage during the pulling in operation and enable you to replace it, if it is defective, prior to repositioning your rigging apparatus, cable reels, barricades, manhole guards etc.

Clean Up Job Site. Once the cable has been pulled in, been confirmed as being good, and sealed, clean and properly store tools and equipment. Although not a popular task, these actions are important to the job. By taking care of your tools and equipment you can be assured that they will continue to provide safe dependable service and be where you will expect to find them when the next job comes along.

Cable in Duct Upgrades. Under ordinary circumstances, underground cable is removed only when repair in the field has become impracticable or the load requirement has been upgraded. In these situations you may be able to install replacement cable, while cutting out the steps of rodding the duct, installing a pulling in wire, and installing a pulling in rope or winch line. If the pull is expected to be relatively easy you may be able to use the existing cable as the “pull rope”. Attach the new replacement cable to the existing cable using basket grips and a swivel between them. Perform all other procedures as required.

Safety. There are some safety factors to consider when installing cable in an underground duct system. Of primary importance is that all work crew members assigned to the installation be intimately aware of their position responsibility and be thoroughly acquainted with all applicable sound and hand signals. The crews should have a full compliment of trained personnel to perform the position duties required at each manhole. As a minimum, the cable feeding manhole must have a crew consisting of a crew supervisor, cable reel tender, and cable feeder/lubricator. The crew supervisor is responsible for monitoring the overall job, interpreting signals, relaying communications, and acting as the worksite safety monitor. The cable reel tender is required to inspect the cable for damage as it is being fed into the manhole and to ensure that the cable comes off of the reel in a controlled manner. The cable feeder/lubricator is needed to ensure that the cable feeds properly into the cable guide and monitors the lubricant level. The crew assigned to the pulling manhole should consist of a manhole supervisor, a rigging equipment tender, and truck operator. The manhole supervisor interprets signals, relays communications, and acts as the manhole safety monitor. The rigging equipment tender monitors the pull rope or winch line as it feeds through the rigging equipment and watches for the advanced cable marker. The truck operator controls the pull rope or winch line take-up speed.

Other safety factors to consider when undertaking cable installation or removal operations are:

  1. Before entering a manhole or excavation, test for dangerous gases or oxygen deficiency using correct testing procedures.
  2. Protect all open manholes, trenches, or other excavations with guards, barricades, covers, flags, or other suitable warning devices.
  3. Do not bring flames closer than 10 feet to a manhole.
  4. Use only standard, approved lighting apparatus in manholes.
  5. Stay clear of the pulling equipment when placing cable in and removing it from the manhole.
  6. Before the initial pull is made on the cable, personnel should leave the manhole. Also, at any other time when the pulling line is tensioned to an unusually high degree, no one should be inside the manhole area.
  7. Exercise caution when entering and leaving manholes located on traveled thoroughfares.
  8. Always use a ladder to enter or leave manholes and have hands free of materials or tools when ascending or descending the ladder.
  9. A co-worker should always be stationed by the manhole entrance to provide help and perform the duties of a safety person. As the safety person, that co-worker should initiate conversation with the worker at 10 minute intervals to make sure everything is all right.

8.6.0 Underground Transformers

Transformers used in support of underground distribution systems will serve the same purpose as pole mounted transformers used in an overhead system. However, the procedures to install them are very different.

Underground transformers are either installed on pads (pad mounted) or in vaults. The term “Vault” identifies an enclosure above or below ground which is used for the purpose of installing, operating or maintaining electrical distribution equipment or cables. See Figure 167.

Figure 167 – Underground vault.

How a transformer is installed will depend largely upon where it will be located in the system and what it is being connected to. Besides providing power to the customer, transformers must be installed properly to ensure that they are kept at a safe distance from other equipment and people.

8.6.1 Pre Installation Requirements

8.6.1.1 Transformer Size

Prior to the actual installation, your first order of business is to determine the size or KVA rating of the transformer to be installed. The electrical engineer or shop supervisor will normally select the size of the transformer; however, if that does not occur, you will be able to make the determination based on the customer’s proposed load requirement.

If the transformer being installed is replacing a faulty one, the same size is normally installed. The KVA rating, voltage levels, and all necessary information about the transformer can be found on the data plate usually located inside the transformer cabinet on the secondary side.

Other factors that affect the selection process are the physical size and weight limitations posed by the customer’s facility. You will need to determine if there is enough room in the vault or outside pad area large enough to accommodate the size of a particular replacement transformer. Is the doorway large enough to accept the transformer, and is the floor or support pad sufficient to support the weight? The physical size and weight will also help you decide what type of vehicle is required to transport the transformer to the job site.

8.6.1.2 Transformer Weight

You must know the weight of the transformer to determine the kind of vehicle and rigging equipment you will need to transport and install the transformer. The weight of most transformers can be found on the data plate. With this information, you can select installation equipment and a sling capable of lifting and moving the transformer. If either of these items is underrated they may fail, causing the transformer to crash to the ground during the installation process. This could obviously cause external and internal damage to the transformer. If you cannot determine the weight, notify the shop supervisor for assistance.

8.6.2 Installation Methods

The methods used to install transformers in Underground distribution systems will be based on the type of equipment used to perform the task and the actual location of the installation. Because of size and weight considerations, installation of most transformers will require the use of heavy equipment of some sort and experienced licensed operators.

8.6.2.1 Line Truck/Crane

Most transformers you will install on outside pads can normally be transported and placed in position using a line maintenance truck. However, some of the power transformers (see Figure 168) might exceed the lifting capacity of the line truck. In this case, you may require a crane or heavy capacity forklift to assist you in positioning larger transformers.

Figure 168 – Power transformer.

8.6.2.2 Roll on Conduit

Some transformer installations will be performed inside a vault. Since the final positioning of a transformer inside an enclosed room would be difficult using a large support vehicle, you will need an alternate means of moving and positioning the transformer.

Rigid metal conduit (RMC) can be used to roll transformers to their final position inside a vault. A line truck or crane can be used to position the transformer near the doorway and on top of the conduit that has been placed on the ground.

8.6.2.3 Forklift

You can use a forklift if the vault has a door large enough and a ceiling high enough to allow it to enter. No matter what piece of equipment you use to position the transformer, the equipment and the attachment slings must be of sufficient size to handle the weight of the transformer.

8.6.3 Installation Procedures

8.6.3.1 On Pad

To install a transformer on a pad, attach the sling(s) to the “manufactured” lifting points already on the transformer (see Figure 169). These lifting points are positioned over the tank containing the oil and transformer windings since this is where the majority of the weight is located. Do not attach slings to any point other then those designed by the manufacturer. Attach the other end of the sling(s) to the piece of equipment being used to lift the transformer. Position taglines near the bottom of the transformer prior to lifting. These taglines will enable you to maneuver the transformer as needed and keep you a safe distance away from it and any crush points should it fall or swing out of control.

Figure 169 – Lifting point on a pad-mount transformer.

8.6.3.2 In Vault

The procedures to install a transformer in a vault are basically the same as those for installing a transformer on a pad. The only exceptions are the use of taglines and support vehicles. Because of the space limitations of vaults, the support vehicle will only be used to transport the transformer to a close proximity of the vault’s entrance. From there, unless the support vehicle is a forklift capable of driving through a door, the

transformer is laid on top of rollers (Rigid conduit) and pushed to the desired location. As the transformer is pushed, it will roll over top of the conduit. As it rolls over and past each stick of conduit, that piece of conduit is taken from the back and placed in front of the transformer to continue the moving process until the transformer reaches its final position.

8.6.3.3 Anchor

Whether the transformer is installed on a pad outside or within a vault it will need to be anchored down. Anchoring ensures the transformer does not move and cause damage to the conduits and/or the cables being connected to it. Bolting it down to the floor or concrete pad generally does this.

8.6.3.4 Restricted Access

The last step in the installation process is to either install or verify the installation of a secure fence and posted warning signs for transformers installed outside. (Note: An enclosed fence is not required for enclosed pad-mount transformers) All transformers must have warning signs identifying the equipment as being a “High Voltage” danger. These warning signs can be posted either directly on or around the transformer’s immediate area.

8.7.0 Isolate, Troubleshoot and Trace Underground Cable

When a system’s circuit or equipment does go down, you will be required to find the problem (troubleshoot) and make the necessary repairs. Obviously you will want to perform these tasks with the system power turned off. When you take the necessary actions to de-energize the circuit or equipment, it can be said that you have "isolated" them from the energized distribution system. You will need to locate underground cable, identify what type of faults the cable may have, and create a safe work environment to perform troubleshooting and make repairs as necessary.

8.7.1 Ground and Isolate

8.7.1.1 Reasons for Isolating and Grounding of Circuits

There are many reasons you may need to isolate and ground a portion of your distribution system. It may be required to perform maintenance or repairs to the system or to prepare to install larger transformers for a system upgrade.

Whatever the reason, you must perform isolation and grounding procedures whenever you open or close a switch or device that is out of sight of the work area and whenever the power will be turned off to a section of a circuit or piece of equipment.

The procedures have been developed to protect life and property. They must be used to clear cable circuits and equipment for the safe accomplishment of work in a DE- ENERGIZED condition. These actions will enable you to perform work on electrical circuits and equipment in a safe, systematically controlled manner.

8.7.1.2 Tools and Equipment Required to Isolate and Ground Circuits

Electrical Switchgear. The main piece of equipment used to isolate a circuit is some type of switchgear. Switchgear provides a means to stop the flow of electricity to the entire distribution system or just a portion of it. Switchgear can be found in the substation, at the junction of feeders, in between two circuits, or anywhere the engineer decided it was necessary to provide a means to isolate the circuit. The main purpose of switchgear is to isolate the circuit.

Out-of-Service Protection. Before performing any repair on a piece of electrical equipment, be absolutely certain the source of electricity is open and tagged or locked out of service. Whenever you leave your job for any reason or whenever the job cannot be completed the same day, be sure the source of electricity is still open or disconnected when you return to continue the work. Seabees have died because they did not follow proper tag and lockout procedures. These procedures are a must. It takes time to do it, but it is worth the time to save your life.

Safety Color Codes. OSHA has established specific colors to designate certain cautions and dangers. Table 6 shows the accepted usage. Study these colors and become familiar with all of them.

Table 6 – OSHA safety color codes.
OSHA SAFETY COLOR CODES
RED Fire protection equipment and apparatus; portable containers of flammable liquids; emergency stop buttons; switches
YELLOW Caution and for marking physical hazards, waste containers for explosive or combustible materials; caution against starting, using, or moving equipment under repair; identification of the starting point or power source of machinery
ORANGE Dangerous parts of machines; safety start buttons; the exposed parts (edges) of pulleys, gears, rollers, cutting devices, and power jaws
PURPLE Radiation hazards
GREEN Safety; location of first aid equipment (other than fire fighting equipment)

Lockout/Tagout Procedures. Utilization of proper Lockout/Tagout procedures is required as described in 29 CFR 1910.147. This standard covers the servicing and maintenance of machines and equipment in which the unexpected energization or start up of the machines or equipment or release of stored energy could cause injury.

Lockout Device.A Lockout Device is a positive means to hold an energy-isolating device in a SAFE position in order to prevent the energizing of a machine or equipment. A single padlock may be used for single, individual lockout procedures. See Figure 170. Examples are:

Figure 170 – Locking devices.

8.7.1.2.2. 8

Tagout Device. A tagout device is a prominent warning device which can be securely fastened to an energy isolating device. It will indicate that the energy isolating device and equipment being controlled WILL NOT BE OPERATED until it’s removal. The tagout device is constructed and printed so that exposure to weather conditions will not cause it to deteriorate. It shall be substantial enough to prevent inadvertent or accidental removal with the use of excessive force or unusual techniques. Tag attachment means, shall be of a non-reusable type, hand self-locking non-releasable with strength of no less than 50 pounds. The tag shall warn against hazardous conditions if the machine or equipment is energized. The tag shall include a legend such as:

* DO NOT START

* DO NOT OPEN

* DO NOT CLOSE

* DO NOT ENERGIZE

* DO NOT OPERATE

It should have the name of the person installing the tagout as well as the date of installation. The tag will be affixed to the individual lockout device. If it cannot be attached directly it will be placed as close as possible. Lockout and Tagout devices will be standardized within the activity by color, shape and size. Tagout devices will also be standardized in print and format. An example of a Tagout Device is shown in  Figure  171.

Figure 171 – Tagout device.

Ground Set. Grounding is accomplished by using a grounding set. Grounding sets come in many styles, but all are designed to short the phases together and then take them to ground. In the previous block you were introduced to grounding sets specifically designed for overhead distribution system grounding operations. It is important for you to understand that those same grounding sets will not be used in support of underground distribution systems due to the differences in equipment design and the use of cable terminations verses open conductor. A quick way to identify an underground grounding set is by the end clamps. Underground grounding sets use clamp-type clamps or elbows on the end of the cable. Because of the importance of grounding, perform a visual inspection of any and all grounding sets prior to leaving the work center. Make sure that you have the proper type of grounding set for the type of electrical system you are going to be working on. While doing the visual inspection, pay particular attention to the condition of the grounding set’s cable and clamps.

Cable. The cable of any grounding set must be large enough to handle the induced current and maximum fault current that the source, such as a substation breaker, can deliver. During a fault condition the cable can whip back and forth. Therefore, it must be made of a flexible, stranded conductor. The conductor will also have a 600 volt insulation rating. Most shops will have a ground set large enough to be used anywhere on the installation.

Clamps. The clamps of an underground grounding set must be approved grounding clamps of the highest quality of construction designed for the specific purpose of grounding. As is the case with the grounding cable, the grounding clamps must be of such size and construction as to carry the induced current and maximum fault current that could flow at the point of grounding for the time necessary to clear the line. Clamps on the “hot” end of the cable may have insulated sticks permanently attached or be operated by using an insulated “shotgun” or rigid splice stick. See Figure 172.

Figure 172 – Shotgun stick.

The use of hot line clamps is not acceptable. Hot line clamps are not designed to handle large fault currents. The approved grounding clamp must also be permanently attached to the cable. A live front transformer, shown in Figure 173, requires the use of a clamp type ground set, shown in Figure 174.

Figure 173 – Live-front transformer.


Figure 174 – Clamp-type underground ground set.

If grounding a dead front type transformer, the ground set may use elbows instead of clamps. Again, an approved elbow must be used as part of the ground set. As a general rule, if you purchase a ground set from a manufacturer, you are buying approved equipment. If you make a ground set out of material you have laying around the shop, you are asking for trouble. Do not make your own grounding set. Buy an approved grounding set from a manufacturer.

Plan and Record Outage Details. Isolating a circuit or system component requires careful planning. Even in an emergency, you will need to develop a plan prior to working on any circuit or high voltage equipment. Any plan you develop will require you to refer to base distribution maps and draw on the knowledge of co-workers familiar with the distribution system in order to document the blocking and tagging procedures on the Lockout/Tagout Log. The more detailed you make the locking and tagging instructions, the better off you are.

When developing your plan, keep the customer in mind. Limit the isolation to areas that will have the least affect on customers. Once you have finished developing your plan, have others review it and get their opinion. No matter how much knowledge you may have about the system, you may have left out important steps. Others may be able to fine-tune your plan, making it the best possible product.

Isolate Section. Once you have devised a plan, it will be time isolate the circuit or equipment. However, before the work actually starts it is common practice for the shop supervisor to brief every member that will take part in the job on all of the step-by-step procedures to accomplish the job, starting with the isolation procedures, through the procedures required to perform the installation, repair, or maintenance, and finally the procedures required to re-energize the circuit or equipment. Everyone must know exactly what must be done and when, before any work begins. When working with electricity, safety must be your prime concern.

After completing the required actions, make sure you record the time on the Lockout/Tagout Log. If at any time something seems out of place, stop the operation and discuss it with your co-workers and/or supervisor.

Block Movement of Switchgear Operation. Opening a switch does no good if you do not lock it out. Locking the switch in the open position and applying the appropriate tag to warn others will ensure your personal protection and that of your coworkers. Make certain the tags are completely filled out with the correct information. Wrong information on a tag is just as bad as not tagging it at all. See Figure 175.

Figure 175 – Lock.

If a switch is operated by a motor, the motor must be disconnected from the system. Some switches can be operated from a remote location such as inside the blockhouse at the substation. In this instance, the motor on the switch must be disconnected and tagged to prevent it from being inadvertently operated. Group maintenance requires a lockout device enabling EACH WORKER a place to position an individual lockout device.

8.7.1.4 Procedures to Install Grounding Set

Isolate the Circuit. Prior to installing a ground set, you obviously need to de-energize the system. That was the purpose of the detailed locking and tagging plan. Remember, your first priority when working on any high voltage circuit is the protection of personnel. Always think safety!

Check for Voltage. Use a high voltage phase tester to verify that the circuit or equipment you will be working on has been de-energized prior to installing a grounding set. One thing of which you need to be aware is that underground high voltage cable acts like a capacitor. It will store a charge even after the cable is de-energized. Because of this, do not make contact with any exposed conductor or elbow electrode prior to grounding it.

Prior to testing, you must know the system voltage so that you will know what reading to expect during the test with the high voltage phase tester and that your tester is capable of reading the level of voltage on the system. If the system voltage is higher than the rating of your high voltage phase tester, the meter may fail and cause you serious injury.

When testing dead front equipment, use adapters on the high voltage phase test set. Screw bushing adapters to the end of the phase tester to test the bushings on the equipment for voltage. Along with bushing adapters, you may need feed thru bushings (see Figure 176).

Feed-thru bushings allow you to “park” a loadbreak elbow on one side of the bushing so you can test the other bushing of the feed thru for voltage. Remember to treat these cables as though they are energized. They are not safe until they have been grounded.

Figure 176 – Feed-thru bushing.

Always use universal hot sticks (Figure 177) when using the high voltage phase test set, see Figure 178. Do not use the phase test set with your bare hands or with just a set of rubber gloves on. If you detect voltage, leave the meter on long enough to get a clear meter indication. This meter is not designed for continued contact with energized circuits for long periods of time. However, make sure you leave the meter on long enough to provide a clear and concise reading. This is no time to “think” you know what the meter indicated. You must be certain.

Figure 177 – Universal stick with switch stick attachment.


Figure 178 – High voltage phase tester.

When you test cable or equipment for voltage, you must follow a very definite set of procedures. First, test the operation of the meter by measuring the voltage of a known "live" conductor. Next, use the meter to test each phase of the cable that is supposed to be "dead". If no voltage was indicated on the de-energized cable, again test the meter on a "live" conductor to ensure it is still working properly. See Figure 179.

Figure 179 – Voltage detector.

Other voltage meters may be used to test the cable. They are the digital voltage indicator and the high voltage audible indicator. Some phasing sticks use a glow lamp to indicate the presence of voltage instead of a meter reading

8.7.1.4.3

Install Ground Set. Once you have determined there is no voltage present on the cable or equipment, it is time to apply the grounding set. You must securely ground the grounding set before making connections the cable or equipment. Do this by firmly clamping the ground clamp to a good ground, such as a counterpoise, primary neutral or grounding electrode.

Most underground equipment has a grounding rod already installed and connected to the case. If for some reason there is not ready access to an established ground, you must install a temporary grounding rod. After you have done so, attach the free clamps of the grounding set to the conductor(s), see Figure 180, using an approved and tested hot stick. As a further safeguard, stand as far away as you safely can in the event an arc develops because the equipment is energized. Once all the phases have been grounded, the circuit or equipment is considered safe and ready to be worked. In removing grounds, the clamps must be detached from the conductors first.

Figure 180 – Ground set clamps and lead.

8.7.2 Safety

The task of isolating a circuit or equipment and installing grounding sets is filled with safety concerns. Of paramount importance is that you know your system voltages. Only by knowing these voltages will you know what to expect when taking voltage readings. When taking readings using a phase test set or applying grounding leads, you will want to make sure you use hot sticks and personal rubber equipment. Never assume a cable or equipment is de-energized. Always check for voltage before installing a grounding set and only use ground sets that will handle the maximum fault current of the system you are working.

Prior to installing a ground set, perform a pre-use inspection. Check the cables to see that none of the strands are broken. Make sure that all the cables are securely attached to the clamps and inspect the clamps to see that they operate freely.

You must strictly adhere to and 100% complete isolation procedures before attempting to work on any cable or line equipment without personal protective gear. Remember, if a cable or equipment has not been grounded, it is not dead!

 

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9.0.0 TEST of POWER DISTRIBUTION SYSTEMS

9.1.0 Basic Measuring Equipment Precautions

When using measuring instruments, you must observe certain precautions. For example, it is especially important to be careful in using an ammeter because of its low internal resistance. If mistakenly placed across a voltage source, the meter can be damaged. Always break the circuit and CONNECT AN AMMETER IN SERIES with one meter lead going to each point of the circuit breaker to measure an unknown quantity. Be sure to de-energize the circuit before making or breaking the connections.

When using either ammeters or voltmeters ALWAYS start at the HIGHEST meter range. Then drop down to a lower scale range if necessary. This practice protects the meter from injury if an attempt is made to read a high value in a low range. You will also minimize damage to instruments if you form a habit of placing the range selector switch in the highest range position after you have finished using the instrument.

Observe polarity on all direct-current measurements. Take care to connect the positive terminal of the source to the positive terminal of the meter and the negative terminal of the source to the negative terminal of the meter. This action ensures that the meter polarity matches the polarity of the circuit in which the meter is placed.

Be careful to avoid dropping a meter or subjecting it to excessive mechanical shock. Such treatment may damage the delicate mechanism or cause the permanent magnet to lose some of its magnetism.

Take care to avoid connecting the ohmmeter across circuits in which a voltage exists, since such connection can damage the instrument. Secure power first.

 

Note

All capacitors must be discharged before the ohmmeter prods are connected in the circuit. Charges remaining on capacitors after the applied voltage has been removed can severely damage the instrument.

Always turn ohmmeters OFF when finished. This action will avoid discharge of the internal battery if the test leads are shorted inadvertently.

It is important that you remember to use a low voltage megger to test low-voltage insulation. Application of high voltage may initiate insulation breakdown. Do not use low voltage meggers to test high voltage insulation because an inaccurate reading may result from the comparatively small output voltages available from this instrument. Be careful whether using high or low range meggers. Dangerous voltages exist at meter terminals and leads.

9.2.0 Test Equipment

9.2.1 Digital Multimeters

There are many different types and styles of autoranging digital multimeters designed for the professional at work in the field. These instruments stand up to the use and abuse of everyday service and electrically insulate the user from potential shock hazards. They have electronic overload protection against accidental application of voltage to resistance and continuity circuits. These characteristics, combined with their rugged construction, make them durable and reliable instruments. See Figure 181.

Figure 181 – Digital multimeter.

Maintaining and cleaning these instruments is easy. Maintenance consists of periodic cleaning, battery replacement, fuse replacement, and recalibration. Perform calibration on these meters every year. Clean the exterior of the instrument with a soft, clean cloth to remove any oil, grease, or grime from the exterior of the instrument. Never use liquid solvents or detergents. If the instrument gets wet for any reason, dry it using low pressure “clean” air at less than 25 psi. Use care and caution while drying around the display protector and areas where water or air could enter the interior of the instrument.

 

Caution

All resistance measurements should be taken on de-energized circuits ONLY

 

Warning

When using compressed air for cleaning, wear chemical splash goggles. Do not direct the air toward eyes or skin.

9.2.2 Vibroground

The vibroground functions on the null balance principle. The current flows through a calibrated potentiometer that causes a voltage drop, which is fed to the primary of the ratio transformer, inducing a voltage drop in the secondary causing a current flow in the measuring circuit. See Figure 182.

Figure 182 – Vibroground.

This current cancels the current in the measuring circuit due to the voltage drop across the ground resistance between the electrodes connected to terminals X and 1.

When the potentiometer and range switch are adjusted so that the two currents exactly cancel, the galvanometer needle will rest in the zero position.

9.2.3 Biddle Direct Reading Meter

The Biddle direct reading meter (Figure 183) measures the resistance of ground connections to earth, thereby helping to determine the effectiveness and integrity of such grounding systems. It can also measure soil resistivity and determine optimum locations for earth electrodes. The resistance to earth ground should be less than 25 ohms and as close to 5 ohms as possible.

Figure 183 – Biddle direct reading meter.

An AC test current, generated by the instrument, is passed between the ground under test and a current electrode (or reference ground). This potential drop to a separate electrode (or reference ground) is applied to a bridge circuit and nulled with a three-decade variable resistance. At balance, ground resistance in ohms is read instantly from the digital decade switches. This null balance method means that at balance no current flows through the potential electrodes, and therefore, their resistance does not affect the reading.

9.2.4 Clamp on Ammeter

The Clamp On ammeter is used to check current on secondary distribution mains, service drops, and individual dwelling circuits. The clamp on ammeter allows it to fit around a conductor to measure AC or DC current without breaking the circuit. See Figure 184.

Figure 184 – Clamp-on ammeter.

9.2.5 Phase Rotation Meter

Phase rotation meters are used to check for proper phase rotation of three-phase equipment being put into service for the first time. See Figure 185.

Figure 185 – Phase rotation meter.

It is also used to check phase rotation of alternators (generators) that will be operated in parallel.

 

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10.0.0 MAINTENANCE of DISTRIBUTION SYSTEMS

10.1.0 Overview

The elements, accidents, and willful vandalism cause most damage to power distribution equipment. To repair these damages, the lineman requires experience, a total commitment to safety, and the knowledge repair the system as quickly and economically as possible.

10.2.0 Maintenance of Poles, Timbers, and Crossarms

The maintenance required on the poles, timbers, and crossarms in a power distribution system is minimal. Normally, this equipment lasts for 20 years or more. The following problems may occur, however, and create a need for maintenance action:

10.3.0 Wood Pole Maintenance

Wood poles are treated with preservatives to prevent decay, but small organisms, insects, and fungi all contribute to the breakdown of the wood preservatives. The life of a pole can be extended by inspections and treatment, when necessary, to stop pole decay.

The inspection would normally include sounding the pole by hitting it with a hammer from belowground level to approximately 6 feet above ground to determine obvious defects. It also includes boring the pole to determine the presence of internal voids. Poles with internal decay can be treated with insecticides. External decay is removed, and the area treated with preservatives and wrapped with a moisture-proof barrier. Poles weakened excessively by internal or external decay must be reinforced or replaced.

10.4.0 Maintenance of Hardware, Conductors, Accessories, and Guys

Other items that may require maintenance are the hardware, conductors, accessories, and guys.

10.5.0 Interference Elimination

Another important area of maintenance is noise interference elimination in the power distribution system.

Power lines may be a source of interference with radio communications. Conductors, insulators, and hardware contribute to this interference by spark discharges, localized corona discharge, and cross modulation.

10.5.1 Spark Discharges

Spark discharges occur when localized excessive voltage stress exists. A conductor may become partially insulated by corrosion products or an insulator partially conductive because of cracks. A third source of stress occurs when a conductor is separated from another metallic part on a pole only by a small air gap.

10.5.2 Corona Discharge

“Corona” is defined as the luminous discharge due to ionization of the air in the vicinity of a conductor when the voltage gradient exceeds a certain critical value.

10.5.3 Cross Modulation

Cross modulation (often the result of a corroded connection that causes nonlinear rectification of currents) may occur when splices are made by twisting the conductors, rather than using a tighter mechanical splice. Additionally, when conductors of dissimilar metals are joined, corrosion occurs unless special connectors designed for the specific combination of metals are used.

Remedies for conductor, insulator, and hardware interference are relatively simple. Remember, the condition for hardware interference exists whenever two pieces of hardware are not securely bonded to each other or are permanently separated by too short an air gap.

10.6.0 Transmission Line Inspection

Transmission lines should be inspected periodically, especially after construction or severe weather.

10.6.1 What to check for

10.6.2 Inspection Intervals

10.7.0 Distribution Line Inspection

Linemen frequently work on distribution lines to provide facilities for new customers or to make modifications. Linemen should thoroughly check the pole line and equipment each time they perform such work.

10.7.1 What to check for

10.7.2 Inspection Intervals

A scheduled inspection should be completed every 5 years or more often if a circuit has a record of poor reliability. These inspections must be done properly and as scheduled. Failure to do so can cause complete equipment or electrical service breakdown. BUT, most importantly could cause serious injury or death.

10.8.0 Capacitor Maintenance

Switched capacitors should be inspected annually, prior to the time they are automatically switched on and off.

Capacitor bank oil switches should be maintained on a schedule related to the type of on/off controls installed at each bank.

Capacitor switches are commonly removed from the line and replaced with a spare during the season they are not normally operated. The main switch is more effectively maintained in the shop. The maximum number of open and close operations between inspections should not exceed 2500.

10.9.0 Recloser Maintenance

There are various types of relcosers and their maintenance schedules vary by type.

All line reclosers will be installed with bypass provisions and a means for isolating the equipment for maintenance.

10.10.0 Pole Mounted Switch Maintenance

The lineman should check group mounted or single pole switches each time they are used.

10.10.1 What to check for

10.10.2 Inspection Intervals

Switches that have not been adequately inspected (rural areas) will be inspected at least every 5 years.

10.11.0 Underground Distribution Circuit Maintenance

Underground circuits originate at a substation or riser pole. Various components of these circuits, such as risers, switchgears, and cables must be inspected and the inspections properly documented.

10.11.1 Riser Maintenance

Risers should be inspected accomplished when overhead lines are being inspected and maintained.

10.11.1.1 What to inspect

10.11.2 Switchgear Maintenance

Switchgears should be inspected annually.

10.11.2.1 What to inspect

10.11.3 Underground Cable Maintenance

10.11.3.1 What to inspect

10.11.4 Records

Records must be accurate and maintained up to date. At a minimum, records should include the following information:

Records serve a vital function and are the basis for predicting equipment failure and for selecting future equipment needs.

10.12.0 De-energizing Lines for Maintenance

Prior to de-energizing a line for maintenance, you should make arrangements with the proper authority. You should also notify the affected customers prior to taking an apparatus out of service.

Before performing any maintenance, assure that:

Drawer breaker is removed from the switchgear.

Testing and grounding lines, requires the following equipment and safety gear:

The procedure for testing and grounding lines is:

  1. De-energize the circuit
  1. Test each exposed terminal
  1. Connecting the grounding cluster

 

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Summary

Your ability to safely install and troubleshoot distribution systems is paramount. This course addressed the components that make up both overhead and underground distribution systems. It also presented the safety and test equipment available to you. These are the tools of your trade. You need to understand these components on order to effectively design and construct a power distribution system

 

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Review Questions

1.  A power distribution system includes all the parts of an electrical system between the power source and the customer’s service entrance.

A. True
B. False

2. What is the primary purpose of a line crew?

A. To meet the project completion date
B. To ensure on the job safety
C. To control cost overruns
D. To assist the pole crew

3. A hard hat for a line crew member must be rated to withstand what maximum voltage?

A. 5,000
B. 10,000
C. 20,000
D. 30,000

4. What is the minimum required clearance, in feet, between crew personnel and a 20,000-volt circuit?

A. 8
B. 6
C. 3
D. 2

5. What is the most popular type of anchor?

A. Rock
B. Screw
C. Deadman
D. Expansion

6. A “down guy” used at the end of a pole line to counterbalance the pull of the line conductors is what type of guy?

A. Balancing
B. Counterbalance
C. Counteracting
D. Terminal

7. When should you install grounding sets on a jobsite?

A. When working on new construction
B. When the disconnecting means is not in sight
C. When the line crew is spread out over a long span of construction
D. Just prior to job completion

8. Guys installed to protect the facilities and limit the damage if a conductor breaks are known by what term?

A. Line guys
B. Storm guys
C. Span Guys
D. Both A and B

9.  An anchor guy with a horizontal strut at a height above the sidewalk sufficient to clear pedestrians is known as a head guy.

A. True
B. False

10. What type of guy is used to transfer the strain on a pole to another structure?

A. Arm
B. Head
C. Span
D. Stub

11. What type of guy is used on steep hills to counteract the downhill strain of the line?

A. Arm
B. Head
C. Span
D. Stub

12. What type of guy is often installed to obtain adequate clearance for guy wires extending across a street or highway?

A. Arm
B. Head
C. Span
D. Stub

13. What type of guy is used to counteract the force caused by an uneven number of dead-end conductors on one side of a crossarm than on the other?

A. Arm
B. Head
C. Span
D. Stub

14. What type of guy is installed between a line pole and a pole on which there is no energized equipment?

A. Arm
B. Head
C. Span
D. Stub

15. What is the purpose of guying a pole?

A. To maintain proper leveling of crossarms
B. To keep a pole-mounted transformer from pulling a pole out of alignment
C. Counteract the unblanced forces that dead end connectors impose on the poles
D. To aid in the proper sag of individual wire spans

16. When there is no excessive strain, single crossarms should be installed in a straight line in what manner?

A. Every other crossarm should face the same direction
B. All crossarms should face north if the distribution system is running north and south
C. All crossarms should face east if the distribution system is running east and west
D. All crossarms should face the same direction when line angle change is less than 10°

17. Double crossarms are used for which of the following purposes?

A. To eliminate excessive strain
B. Lines cross railroad crossings
C. To provide support when two or more transformers are mounted on the same pole
D. All of the above

18. When a branch line makes a right angle change from the main line, what type of crossarm is required?

A. Double
B. Buck
C. Side
D. Single

19. What factor determines the spacing of insulator pins?

A. The length of the crossarm
B. The size of insulator pins
C. The voltage design of the circuit
D. The quantity of insulator pins needed

20 What type of insulator should be used when the right-of-way is narrow?

A. Post
B. Pin
C. Suspension
D. Strain

21. What type of conductor wire is commonly used for line conductors with a wire size smaller than No. 2?

A. Hard-drawn copper
B. Annealed copper
C. Medium-hard-drawn copper
D. Aluminum and aluminum/steel

22. Aluminum wire when compared to copper wire has what percentage of conductivity?

A. 80%
B. 66%
C. 60%
D. 45%

23.  Conductors are classified as solid or stranded.

A. True
B. False

24. What is the AWG’s largest and smallest size of conductors used in distribution systems?

A. 5/0 and 0
B. 2/0 and 0000
C. 3/0 and 20
D. 4/0 and 30

25. What is the purpose of the distribution substation system?

A. It changes distribution circuit voltage to transmission voltage
B. It changes transmission voltage to distribution circuit voltage
C. It changes distribution circuit voltage to usable 120/240 volts
D. It changes three-phase voltage to single-phase voltage

26. What, if anything, can be done to suspension insulators to permit the same-size insulators to be used for higher voltages?

A. Redip the insulators in epoxy
B. Link the insulators in series
C. Insert fiber glass sheets between the insulators
D. Link the insulators in parallel

27.  A distribution transformer reduces the voltage of the distribution circuit to a usable voltage, usually 120/240 volts.

A. True
B. False

28. Which of the following cutouts, when blown, causes the resultant arc to attack the walls of the fiber tube?

A. Open link distribution
B. Closed link distribution
C. Enclosed distribution
D. Open distribution

29. What type of primary circuit is used when residential lighting makes up the substantial portion of the load?

A. Wye-delta
B. Delta-wye
C. Delta
D. Wye

30. What is the purpose of the distribution lightning arresters?

A. They protect the insulators
B. They protect the transformers
C. They protect the fuse cutouts
D. All of the above

31. High-voltage switches are divided into what general classes?

A. Air
B. Oil
C. Vacuum
D. All of the above

32. Of the following types of switches, which one quenches the arc that will possibly occur when a switch is opened by a high voltage situation?

A. Air
B. Oil
C. Vacuum
D. Manual

33.  A secondary circuit carries 600 Vac or less.

A. True
B. False

34. When installing a service drop over a driveway, you must maintain a minimum aboveground clearance of how many feet?

A. 18
B. 16
C. 14
D. 12

35. A three-phase, air-break switch is opened in what manner?

A. Manually, one phase opens at a time only
B. Automatically, one phase opens at a time only
C. Manually or automatically, all phases open at the same time
D. Manually or automatically, one phase opens at a time

36. What type of high-voltage switch should NOT be opened under load?

A. Air
B. Oil
C. Vacuum
D. Manual

37.  The purpose of a disconnect switch is to isolate a line so it is dead electrically.

A. True
B. False

38. High-voltage oil switches are immersed in oil for what primary reason?

A. To break the switch
B. To keep the switching mechanism lubricated
C. To break the circuit when the switch is opened
D. To keep the switching mechanism cool

39. An oil recloser can perform which, if any, of the following actions?

A. It automatically recloses the circuit which has opened for an overload condition in the system
B. It carries excessive current for a period of 5 minutes
C. It opens a circuit once an overload fault has cleared
D. None of the above

40. When linemen place a recloser in the “single-shot” mode, it is for what reason?

A. So it resets automatically
B. So it cannot reset automatically
C. So it resets only one time
D. So it resets only three times

41. When may you find all three phases of an oil switch in one container?

A. When the container is large enough to accommodate all three phases
B. When it is important to open all extremely high-voltage switches together
C. When they are pad-mounted only
D. When the voltage is not extremely high

42. An earth auger is designed to dig holes up to how many feet deep?

A. 5
B. 6
C. 7
D. 8

43. What type of construction vehicle is most commonly used to set poles?

A. Utility truck
B. Aerial bucket truck
C. Earth auger
D. Each of the above

44. What is the purpose of putting the face of the pole in the direction of hills?

A. To make all the poles uniform
B. To allow the strain on the crossarms to be against the curve of the poles
C. To eliminate the use of guy wires
D. To conform to a common practice used by all linemen

45. A gain should be installed how many inches from the top of a utility pole?

A. 12
B. 18
C. 24
D. 30

46. To allow for tamping backfill, you should ensure the hole is approximately how many inches larger than the base of the pole?

A. 10
B. 8
C. 6
D. 4

47. When you are raising a pole, which device is used to prevent the sides of the hole from caving in?

A. A butt board
B. A jenny
C. A cant hook
D. A crossarm

48. Normally, when conductors are being strung, they are taken from a reel that is

A. rolled over the ground
B. held solidly in place
C. mounted on an axle that revolves freely
D. placed on its side and left free to turn

49. For what purpose is the neutral conductor placed on a center crossarm pin?

A. To provide a clear space for the lineman to climb through
B. To serve as a way of identifying hot conductors
C. To conform to traditional Navy practices
D. To provide a path for grounding devices

50. Assume you are mounting a crossarm on a pole. After you have set the pole, what steps are necessary to complete the crossarm installation?

A. Leveling the crossarm and fastening the crossarm braces to the pole only
B. Leveling the crossarm and tightening the through bolt only
C. Tightening the through bolt and fastening the crossarm braces to the pole only
D. Leveling the crossarm, fastening the crossarm braces to the pole, and tightening the through bolt

51. When wires have been pulled to approximately the desired position, a lineman should measure the sag at what location(s)?

A. On the end nearest the cable reel
B. At the center of the span
C. In a span on either end of the group of spans
D. On the end farthest from the cable reel

52. To ensure that lines are installed correctly, you should use what method(s) to measure line sag?

A. Traction dynamometer
B. Target sighting
C. Timing vibration
D. All of the above

53. After stringing and sagging the conductors properly, when should you tie the conductors to the insulators?

A. After ½ hours to 4 hours, depending upon the length of the run
B. After 24 hours, regardless of the size of the wire or the length of the run
C. As soon a possible
D. After exactly 2 hours

54. Concerning the use of tie wire in tying-in conductors, which of the following statements is correct?

A. You should not wrap the tie wire too tightly
B. You should always use new fully annealed tie wire
C. You may reuse tie wires that are long enough
D. You should always use No. 2 tie wire

55. On power distribution lines, pole ground connections are required at which of the following intervals?

A. Every ½ mile
B. Every pole
C. Every pole with equipment
D. Every mile pole

56. On existing distribution lines, the pole ground rods should be (a) how many inches in diameter and (b) how many feet long?

A. (a) 5/8 (b) 8
B. (a) 5/8 (b) 10
C. (a) ¾ (b) 8
D. (a) ¾ (b) 10

57. What distribution system configuration is the simplest and least expensive to build?

A. Radial
B. Loop
C. Network
D. Primary

58. The loss of which of the following components in a radial distribution system will result in an outage on all loads served by the feeder?

A. Cable
B. Primary supply
C. Transformer
D. All of the above

59. Service to a radial distribution system can be improved by the installation of which of the following components?

A. Hand reset circuit breakers
B. Automatic circuit breakers
C. Auto-protected transformers
D. Additional lightning protective devices

60. A network system and a radial system differ in what respect?

A. The type of transformers used
B. The type of fuses used
C. The way the transformer secondaries are connected
D. The way the transformer primaries are connected

61. Which of the fallowing concerns is not addressed when installing a new power distribution addition?

A. Select the straightest and shortest route
B. Route the system in the general direction of future load demands
C. Make the system readily accessible for construction, inspection and maintenance
D. Pole material used

62. What type of pole is considered to be the most economical for power line support?

A. Fiberglass
B. Steel
C. Wood
D. Reinforced concrete

63. Lightning arresters for a distribution transformer should be located between which of the following areas?

A. Primary phase and pole grounds
B. Primary and secondary sides of the transformer
C. Fuse cutouts and the secondary bushings of the transformer
D. Secondary side of the transformer and the service drop

64. Which of the following types of distribution transformers require the installation of external protective devices?

A. Conventional
B. Self-protected
C. Both A and B
D. Completely self-protected

65. What feature does the completely self-protected (CSP) type of transformer have that differs from the other types?

A. A built-in current overload device
B. A fuse cutout mounted to the outside of the transformer
C. A beeper that sounds when there’s trouble within the transformer
D. Two tap changers: one primary and one secondary

66. Which of the following means of disposal should you use for a creosote treated wooden pole?

A. Burning
B. EPA approved landfill
C. Burying
D. Either B or C

67. Which of the following means is used to classify a wooden pole?

A. Length
B. Circumference at the top of the pole
C. Circumference measured 6 feet from the bottom of the pole
D. All of the above

68. The ground resistance between the ground wire and the ground distribution neutral should read no more than how many ohms?

A. 10
B. 25
C. 50
D. 66

69. Which of the following actions will lower ground resistance?

A. Drive additional ground rods
B. Connect additional ground rods in parallel
C. Use larger ground rods
D. All of the above

70. After a capacitor bank has been installed, it should be inspected and checked at what minimum interval?

A. Once a week
B. Once a month
C. Twice a month
D. Once a year

71. Maintenance for an oil switch operating a capacitor bank should be performed after the switch has been operated on and off for what maximum number of times?

A. 0,500
B. 1,500
C. 2,500
D. 3,000

72. What is the purpose of a recloser in a distribution circuit?

A. It opens the circuit in case of a fault, locks the switch in the open position, then recloses the circuit immediately after the fault is corrected
B. It recloses an open circuit automatically after the circuit has the sufficient amount of power
C. It recloses an open circuit only when it is signaled remotely by the substation operator to close
D. It opens the circuit in case of a temporary fault and recloses the circuit a few times until the fault is corrected

73. A recloser could be set to re-close at what maximum number of times?

A. One
B. Two
C. Three
D. Four

74. Which of the following statements describes a difference between a fuse link and a recloser?

A. fuse link has a lower ampere rating
B. A fuse link has a higher voltage rating
C. A fuse link can distinguish between temporary and permanent fault
D. A fuse link cannot distinguish between temporary and permanent fault

75. When working with de-energized power lines, which of the following precautions is the best way to avoid accidentally energizing the lines?

A. Post a watch stander by the power switch
B. Put a lock on the power switch
C. Install short circuiting and grounding: leads to the lines
D. All of the above

76. What is the maximum recommended distance between manholes?

A. 0,400 feet
B. 0,500 feet
C. 0,600 feet
D. 1,000 feet

77. What is the smallest allowable size of a manhole?

A. 2- by 3-foot
B. 3- by 4-foot
C. 5- by 7-foot
D. 6- by 6-foot

78. When determining the size of manhole to be used for transformers, how many cubic feet should you allow per kilovolt ampere rating of the transformer?

A. 1 to 1 l/2
B. 2 to 3
C. 3 ½ to 4
D. 4 l/2 to 5

79. Uppermost ducts installed on a manhole should have a minimum of which of the following depths from the ground?

A. 18 inches
B. 30 inches
C. 3 feet
D. 4 feet

80. Communication cables installed underground should be buried at what minimum depth?

A. 18 inches
B. 2 feet
C. 3 feet
D. 30 inches

81. Before you completely bury an underground cable, what should you place above the cable?

A. Concrete markers
B. Plastic streamers
C. Three-inch layer of sand
D. All of the above

82. A 600-volt direct burial cable should be installed at what minimum depth?

A. 12 inches
B. 18 inches
C. 24 inches
D. 30 inches

83. Which of the following means should be used for water drainage from a manhole?

A. Ducts that slope down from the manhole
B. Pumps installed in the manhole
C. A central drain hole, a dram line, and a sump for the manhole
D. A series of drainage holes bored on the deck of the manhole

84. When a duct line is set in concrete, there should be a minimum of how many inches of concrete around each line of duct?

A. 3
B. 6
C. 9
D. 12

85. Which of the following methods is used to clean ducts?

A. Wiping
B. Vacuuming
C. Rodding
D. Each of the above

86. You are pulling multiple cables through a duct. You should pull the cable at what rate?

A. 25 feet per minute
B. 35 feet per minute
C. 50 feet per minute
D. 75 feet per minute

87. An ammeter has which of the following electrical characteristics?

A. High internal resistance
B. High power consumption
C. Low internal resistance
D. Low voltage rating

88. When an ammeter is connected across a voltage source, which of the following conditions will occur?

A. The circuit will be overloaded
B. The circuit will consume excessive power
C. The ammeter will be damaged
D. The ammeter will read the current in the reverse direction

89. Before breaking a circuit connection for an ammeter, what should be your first step?

A. Set the meter at its highest range
B. Energize the circuit
C. De-energize the circuit
D. Set the meter at its lowest range

90. Before connecting an ohmmeter into a circuit, what step should you do first?

A. Place the meter to its highest range
B. Check the polarity of the meter
C. Make sure current is in the circuit
D. Secure power

91. Before placing the test leads of an ohmmeter into the terminals of a capacitor, what step should you do first?

A. Ground the case of the capacitor
B. Charge the capacitor
C. Discharge the capacitor
D. Ground the ohmmeter

92. You should not use a low-voltage megger to test high-voltage insulation breakdown for which of the following reasons?

A. The megger will be damaged
B. The megger will not read accurately
C. The insulation will be damaged
D. The megger will not indicate any reading

93. To dry a wet digital multimeter, you should use low-pressure clean air at what maximum pounds per square inch (psi)?

A. 10
B. 15
C. 20
D. 25

94. When working on distribution lines, what action should you take to protect your high-voltage rubber gloves?

A. Wear cotton gloves over them
B. Avoid handling sharp objects
C. Wear leather gloves over them
D. Use them only on de-energized circuits

95. How often should rubber gloves be given an air test?

A. Yearly
B. Monthly
C. Weekly
D. Each day, before using the glove

96. What action should you take to protect rubber gloves from mechanical damage?

A. Leave the rubber gloves inside the cotton gloves
B. Leave the rubber gloves inside the leather gloves
C. Store the gloves inside a canvas bag
D. Store the gloves in dry storage

97. Besides mechanical damage, rubber gloves should be protected from which of the following conditions?

A. Moisture
B. Dryness
C. Sunlight
D. Chemical exposures

98. A rubber insulating insulator hood is used to cover what distribution system component?

A. Bare conductor
B. Suspension insulator
C. Strain insulator
D. Post insulator

 

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