Electrical Systems and Plans

As an engineering technician, you will be working with drawings to accomplish various tasks depending on your specific assignment. Just as you need to be familiar with wood framing plans and concrete plans for structural elements, and mechanical plans for plumbing and waste removal, you must also be familiar with electrical plans for power service and distribution. An engineering tech working on a set of drawings or plans must clearly convey his or her ideas (or instructions) to the installer, usually a construction electrician. To do so, you must understand and be thoroughly familiar with the basic methods and functions of materials and fixtures used to install an electrical system. In conjunction with the previous chapters on wood, concrete and masonry, and mechanical systems, this lesson will enable you to prepare construction drawings, revise as-built drawings in the field, and easily incorporate minor design changes.

When you have completed this lesson, you will be able to do the following.

1. Describe the different types of electrical power distribution systems.
2. Interpret different types of electrical plans.


  1. Electrical Systems
  2. Electrical Plans
Review Questions


Occupied buildings, as well as most other structures, require an electrical system to provide power for lighting and various appliances and equipment. An electrical system has three distinct elements:

This lesson only presents the external power transmission and the interior wiring distribution system, with its various materials and fittings used in installation.

1.1.0 Electrical (Power) Distribution System

A complete electrical distribution system brings power from the generating plant through substations, feeders, and transformers to a building’s premises by overhead power poles or underground lines.

This delivery network is generally considered a combination of two sections, the transmission section and the distribution section. The difference between the two sections depends on the function of each at a particular time.

In a small power system, the distinctive difference tends to disappear, and the transmission section merges with the distribution section. The term “distribution section” normally designates the outside lines but the distribution system frequently continues inside the building to include power outlets.

Most power systems use alternating current (AC) rather than direct current (DC), principally because transformers can be used only with AC. An AC distribution system usually contains one or more generators (technically known as alternators in an ac system); a wiring system of feeders, which carry the generated power to a distribution center; and the distribution center, which distributes the power to wiring systems called primary mains and secondary mains. Figure 10-1 illustrates a typical transmission and distribution system.


Figure 10-1 — Typical electrical transmission and distribution system.

Power from the generating station may be distributed by overhead transmission and distribution lines, by underground cable, or by a combination of both.

In most facilities, builders commonly use overhead feeder lines because they are cheaper to build, simpler to inspect, and easier to maintain than underground cables, but underground cable is preferred at airports and runways to prevent hazardous flight conditions.

1.1.1 Overhead Power Distribution

A system may be a three-wire or a four-wire system, depending upon whether the alternators are connected in a delta or wye configuration. Figure 10-2A is a schematic diagram showing a delta connection. The coil marked “stator” represents the stationary coils of wire in the alternator; the one marked “rotor” represents the coils, which rotate on the armature.


Figure 10-2 — Delta- and Wye-connected alternator diagrams.

Power is taken off the stator from three connections, which in the drawing form a triangle or delta. All three wires are live (HOT) wires.

Figure 10-2B shows a Wye (Y)-connected alternator (three-phase, four-wire). N represents a common or neutral point to which the stator coils are all connected. The current is taken off the stator by the three lines (wires), 1, 2, and 3, connected to the stator coil ends; and also by a fourth line, N, connected to the neutral point. Lines 1, 2, and 3 are hot wires; line N is neutral.

In a delta-connected alternator system (Figure 10-2A), the voltage developed in any pair of wires, or in all three wires, is always the same; therefore, a delta-connected system has only a single voltage rating (220 V in Figure 10-2).

In a Y-connected alternator system (Figure 10-2B), the voltage developed differs depending on the combinations of wires. Note in Figure 10-2 that lines 1 and 2 take power from two stator coils (A and C), lines 1 and 3 from two stator coils (C and B), as well as lines 2 and 3 from two stator coils (A and B).

However, neutral (N) and line 2 take power from only one coil (A); neutral (N) and line 1 from one coil only (C), and neutral (N) and line 3 also from only one coil (B).

Therefore, a Y-connected alternator can produce two different voltages: a higher voltage in any pair of (or all three) hot wires and a lower voltage in any hot wire paired with the neutral wire.

Output taken from a pair of wires is single-phase voltage; output from three wires is three-phase voltage. Figure 10-3 demonstrates the voltage cycle of a three-phase system.


Figure 10-3 — One voltage cycle of a three-phase system.

Because of differing benefits derived from each of the two generating systems, some electrical equipment is designed to operate only on single-phase voltage, while other equipment is designed to operate only on three-phase voltage.

This includes the alternators themselves; a system with a three-phase alternator is called a three-phase system.

However, even in such a system, single-phase voltage can be obtained by tapping only two of the wires. 

Figure 10-4 shows an illustration of a three-phase, three-wire overhead power distribution system. Figure 10-5 shows a matching wiring diagram of Figure 10-4.


Figure 10-4 — Typical overhead three-phase, three-wire power distribution system.



Figure 10-5 — Wiring diagram of overhead three-phase three-wire power distribution system in Figure 10-4.

The system has an alternator generating 220 V. From the generating station, threephase, three-wire feeders carry the power overhead to the distribution points where two primary mains branch off.

One of these primary mains carries power to the motor pool for direct (note the three wires) wiring to a three-phase motor designed to operate on 220 V, and (through a transformer) for a lighting system and a single-phase motor, both designed to operate on 110 V (note the two wires).

The other primary main carries power to operational headquarters, living quarters, and the mess hall. This power is also carried through a transformer that reduces the power to the secondary main to 110 V single phase.

Figure 10-6 shows an illustration of a four-wire system serving the same facilities. Figure 10-7 shows a matching wiring diagram of Figure 10-6.


 Figure 10-6 — Typical overhead three-phase four-wire power distribution system.


 Figure 10-7 — Wiring diagram of overhead three-phase four-wire power distribution system in Figure 10-6.

In this scenario, there is a four-wire Y-connected alternator rated at 110/220 V and no transformers are necessary to reduce the power to 110 V single phase for the secondary mains. The neutral wire in a four-wire system exists so that lower voltage can be used in the system. The secondary mains are developed by simply tapping into pairs of wires, one a hot wire and the other the neutral wire. The 220-V, three-phase motor is tapped into the three hot wires delivering the 220 V, three-phase power from the alternator.

Since a three-wire three-phase 220V delivery system needs a transformer to reduce the voltage to the common usage 110 V, we need to know a little more about what a transformer is. A transformer (Figure 10-8) is a device for either increasing or reducing the voltage in an electrical circuit. It does this through a number of coil windings around a core.


Figure 10-8 — Example of step up and step down transformer coil windings.

Step down transformers can range in size from small portables like those for a cell phone charger to permanently mounted heavy ones like those commonly hung with cross-arm brackets attached to an electric pole. (Figure 10-9)


Figure 10-9 — Common step down transformer.

 Long-distance power transmission requires a voltage higher than is normally generated. In this case, a transformer is used to step-up the voltage to that required for long distance transmission (Figure 10-10).


Figure 10-10 — Step-up transformer for long distance transmission.

At the service distribution end, the voltage is reduced again to the voltage required for lights and equipment. A transformer is used there also, but this time it is a step-down transformer.

The voltage must be stepped-up for long distance transmission because of natural resistance; the greater the distance, the greater the resistance, so the greater the force needed to push the current through the transmission line.

Let’s look at Ohm’s Law.

I = E/R


I represents current (in Amperes),
E is electromotive force (in Volts) (also called Voltage)
R is resistance (in Ohms)

From the formula, given a constant voltage (E), than current (I) varies inversely to resistance (R). To maintain the required current (I) as the resistance increases, the voltage, or electromotive force (E), must increase accordingly. The voltage increase makes it possible to use smaller wires or cables. This in turn minimizes the support requirements for aboveground transmission lines and consequently minimizes the cost of the system.

1.1.2 Underground Distribution

Underground power distribution systems are widely used several reasons:

There are three principal categories of underground lines: duct lines, cables buried directly, and conduits located in tunnels. Underground duct systems (Figure 10-11), which consist of manholes, handholes, duct lines, and cables. In general, a representation of the system layout and a list of materials needed to install the system can be found in a standard set of drawings.


Figure 10-11 — Builders preparing to install an underground duct system.

1.2.0 Interior Electrical Wiring System

In electrical terminology, the term “service” means the electrical system that brings power from the exterior power distribution line to a point inside (or on) the building. From there, it is distributed to the building circuits. The key term is “service” and it is used in conjunction with other terms to identify specific segments:

This equipment is the main control and means of cutting off the power supply to the building. It usually consists of a circuit breaker or switch or fuses,

1.2.1 Service Conductors

A service drop conductor runs from a pole to the building. (Figure 10-12) It may be an approved multi-conductor cable or an individual (single) conductor.


Figure 10-12 — Typical service drop.

In either case, it must have thermoplastic, rubber, or other weatherproof insulation.

It must also be of sufficient current carrying capacity to ensure that a prospective maximum load will not create enough temperature change (heat) to damage the insulation.

The NEC® specifies the minimum size conductors allowable for different load (amperage) requirements. 

A service lateral conductor brings power into a building from below ground. (Figure 10- 13).Sometimes these conductors are tied to an overhead distribution system and run down the pole into the ground before they run into the building. In other cases, the entire distribution system, except for the transformer, is underground.


Figure 10-13 — Typical service lateral.

A service lateral may be connected directly to a secondary main or to a transformer if a separate transformer serves the building. It may be installed in rigid conduit (metallic or nonmetallic) or with underground service entrance (USE) cable. Figure 10-13 shows the layout of an underground service lateral run from a transformer to a junction box and through the service entrance to the service equipment.

1.2.2 Service Entrance

The service entrance is the starting point for interior wiring. It brings power from the service conductor (drop or lateral) to the service equipment. (Figure 10-14)


Figure 10-14 — Typical service entrance conductors.

The service drop conductor connects to the service entrance conductor just outside the building. The service entrance conductor may be an approved single conductor run through a protective raceway, such as rigid conduit (metallic or nonmetallic), or an approved type of service entrance cable that does not need raceway protection unless it is likely to be damaged by abrasions or from being struck by passing equipment.

Where single conductors are used, they must be insulated and of the wire size specified by the NEC®. 

Figure 10-14 also shows a service head (also called a weatherhead) which is used with a raceway to provide an entrance for the conductors. The weatherhead is designed to reduce abrasion to the insulation and has a downward facing opening to prevent rain from entering the raceway.

The service entrance conductor leads to the service equipment panel (Figure 10-15) that provides a means of disconnecting the supply source’s service conductors from the interior electrical wiring system.


Figure 10-15 — Typical service equipment panels.

The service entrance panel may consist of a single manually operated switch with a fuse or a circuit breaker. The NEC® sets 60 amperes (A) as the minimum size for fuse type entrance switches and 50A for the circuit breaker type. Rather than burning out like a fuse, a circuit breaker is a protective device that automatically opens the circuit when amperage exceeds its rating. Restoring power is a matter of reducing the amperage draw and closing the circuit again with a switch instead of replacing a fuse.

The NEC® recommends a minimum size of 100-A service for individual residences. However, when no more than two two-wire branch circuits are installed, a 30-A entrance switch may be used.

1.2.3 Panelboard

NEC® defines a panelboard as a single panel, or a group of panel units designated for assembly in the form of a single panel, including buses. (Figure 10-16).


Figure 10-16 — A-Panelboard with breaker panel. B-Panelboard with fuse panel.

A panelboard comes with or without switches and/or automatic over-current protective devices for the control of light, heat, or power circuits of individual as well as aggregate capacity. It is designed for placement in a cabinet or cutout box, in or against a wall or partition, and is only accessible from the front.

A breaker panel uses a thermal unit built into the switch with the breaker preset at the factory to open automatically at a predetermined ampere setting. It may be reset to the ON position after a short cooling-off period.

Lighting panels (Figure 10-17, View A) are normally equipped with 15A single-pole automatic circuit breakers, while power panels (Figure 10-17, View B) may have one-, two-, or three-pole automatic circuit breakers with a capacity to handle the designated load.


Figure 10-17 — A-Lighting panel. B-Power panel.

In most buildings, the service equipment’s entrance switch and panelboards can and should be mounted close to each other. However, they must be placed where service and maintenance can be easily performed. 

They should not block any passage but should be located as near as possible to the center of the electrical load to minimize any unnecessary electrical resistance due to long runs (remember Ohm’s Law). In addition, they should not be placed near exposure to corrosive fumes or dampness.

1.2.4 Conductors

Because of the conducting and ductile properties of copper and aluminum, electrical conductors are usually either drawn copper or aluminum formed into wire. They provide paths for the flow of electrical current. To protect personnel, conductors are usually covered with insulating materials to minimize the chances for short circuits. Atmospheric conditions, voltage requirements, and environmental and operating temperatures are factors to consider in selecting the type of wire with insulating materials for a particular job. Single Conductors

A single conductor (Figure 10-18) may consist of one solid wire or a number of smaller stranded solid wires that share in carrying the total current. A stranded conductor is more flexible, making it more adaptable for pulling through bends in a conduit.


Figure 10-18 — Typical insulated single conductors.

Conductors vary in diameter and use according to their intended electrical current load. Wire manufacturers have established a numerical system to eliminate the cumbersome use of circular mil (fractional-inch diameters) in describing wire sizes. The American Wire Gauge (AWG) Standard (Figure 10-19) provides an easy common reference for wire sizes. Notice the larger the wire gauge number, the smaller the diameter of the wire.


Figure 10-19 — American Wire Gauge (AWG) (partial) 

No. 8 and larger wires are normally used for heavy power circuits or as service entrance leads to buildings.

No. 12 AWG is a wire size used most frequently for interior wiring.

No. 16 or 18 AWG stranded wire is used to conduct current from outlet boxes to sockets in lighting fixtures and is called “fixture wire.”

Multi-wire (Cable) Conductors. A multi-wire conductor (called a cable) is an assembly of two or more conductors insulated from each other with additional insulation or a protective shield formed or wound around the group of conductors. (Figure 10-20) The covering or insulation for individual wires is color coded for proper identification.


Figure 10-20 — Typical insulated multi-wire (cable) conductors.

Two of these common types of cable need more attention. Romex (trade name) (Figure 10-20, View A) is a nonmetallic-sheathed cable (NMC). It comes in sizes No. 14 through 2 for copper conductors and No. 12 through 2 for aluminum or copper-clad aluminum conductors.

It comes with a bare (uninsulated) ground wire laid in intervals between the circuit conductors and under the outside braid. The ground wire is used to ensure the grounding of all metal boxes in the circuit, and furnishes the ground for the grounded type of convenience outlets. Nonmetallic-sheathed cable is used for temporary wiring in locations where using conduit would be unfeasible.

BX (Figure 10-20, View B) is a metallic-armored cable.

BX tends to ground after installation. Small metal burrs on the armor can, because of vibration, penetrate the insulation and cause a ground. The building codes of most cities restrict the use of BX cables to the control circuits for oil burners and similar usage.

BX cables come in sizes from No. 14 to 2 AWG, and each cable may contain one, two, three, or four conductors. The armor on the cable furnishes a continuous ground between boxes.

1.2.5 Insulation

Electrical conductors are available with various kinds of insulating materials. The more common are rubber, thermoplastic, and varnished cambric, but less frequently, special types of paper, glass, silk, and enamel are also used. Multi-wire (Cable) Conductors 

One factor to consider when selecting properly insulated conductors are the NEC® recommendations of insulation type for use in dry, damp, and wet locations. The NEC® considers installation in the following as wet locations:

Another factor to consider is temperature. Different insulations have different maximum temperature ratings. Check the NEC® and any applicable local codes to ensure you use the appropriate insulation for the location and temperature considered in the plans.

The following are a few examples of insulation composition, location application, and maximum temperature rating:

Thermoplastic insulation’s advantages are long life, toughness, a dielectric strength (capacity for insulating) equal to rubber, and it requires no protective covering over the insulation. Common types of thermoplastic insulation are:

Varnished cambric insulation has an insulating quality midway between that of rubber and paper. It is more flexible than paper; its dielectric strength is greater than that of rubber, and ordinary oil and grease do not adversely affect it. It is manufactured in either standard type (black finish) or heat-resistant type (yellow finish). Varnished insulation is restricted to dry locations with applications such as motor leads, transformer leads, and high-voltage cables.

1.2.6 Conduits and Fittings

An electrical conduit is a pipe, tube, or other means in which electrical wires are installed for protection from the elements or accidental damage. Much like plumbing, the conduit’s fittings depend upon the type of pipe or tubing used. Navy construction generally uses rigid, thin-wall, or flexible conduit. Rigid Conduit

Rigid galvanized steel or aluminum conduit is made in 10-ft lengths, in sizes from 1/2 in. to 6 in. in diameter, threaded on both ends, with a coupling on one end. Figure 10-21 shows rigid conduit and various fittings.


 Figure 10-21 — Rigid conduit and fittings.

Again like plumbing’s use of galvanized pipe, installing rigid conduit involves a good deal of cutting, bending, and threading.

An ordinary hacksaw or special wheel pipe cutter is used for cutting, and a ratchet type of mechanical die is used for threading the cut ends.

Bending can be done manually, using a bending tool commonly called a hickey (Figure 10-22), or hydraulically. A hydraulic bender is recommended for making smooth and accurate bends.


Figure 10-22 — Conduit bender (Hickey).

Condulets are a convenient way of making bends on sharp corners and reducing the number of bends made in a run of conduit, especially in conduit intended for exposure to the elements.

Another type of rigid conduit approved for use by NAVFAC is the polyvinyl chloride (PVC) pipe. (Figure 10-23) Plastic conduit is especially suitable for use in areas where corrosion of metal conduit is a problem.


 Figure 10-23 — Builders installing PVC conduit.

PVC’s advantages include light handling weight, ease of installation, and leak proof joints.

Intended primarily for underground wire and cable raceway use, it is available in two forms.

A solvent-type adhesive welding process joins rigid plastic conduit and fittings together.

PVC also comes in sizes of 1/2 to 6 in. in diameter with fittings available from the manufacturer. (For more information on PVC fittings, refer to Article 370 of the NEC®.)

Flexible conduit (called Greenfield) is a spirally wrapped metal band wound upon itself and interlocking in such a manner as to provide a round cross section of high mechanical strength and flexibility. (Figure 10-25)  It is used where rigid conduit would not be feasible. It requires no elbow fittings.


Figure 10-25 — Flexible conduit and fittings. Thin-Wall Conduit

Electric metallic tubing (EMT) or thin-wall conduit is a conduit with a wall thickness much less than that of rigid conduit. (Figure 10-24) It is made in sizes from 1/2 to 2 in. in diameter. Thin-wall conduit cannot be threaded; therefore, special types of fittings are used for connecting pipe to pipe and pipe to boxes.


Figure 10-24 — Thin-wall conduit and fittings. Flexible Conduit 

Greenfield is available in sizes from 1/2 to 3 in. in diameter and in two types: the standard plain or unfinished-metal type and a moisture-resistant type called sealtite, which has a plastic or latex jacket.

The moisture-resistant type is not intended for general use but only for connecting motors or portable equipment in damp or wet locations where connection flexibility is needed.

1.2.7 Wire Connectors

Figure 10-26 shows various types of connectors used to join or splice conductors.

The type used will depend on the type of installation and the wire size.

Most connectors operate on the same principle, that of gripping or pressing the conductors together.

Wire nuts are used extensively for connecting insulated single conductors (both solid and stranded) installed inside of buildings.


Figure 10-26 — Typical cable and wire connectors.

1.2.8 Outlet Boxes

An outlet box is simply a metal (or plastic) container, set flush or nearly flush with the wall, floor, or ceiling, into which an outlet receptacle or switch will be inserted and fastened. Outlet boxes used in Navy construction are usually made of galvanized steel. However, along with the increase of other plastic materials in construction, nonmetallic boxes made of rigid plastic compounds are being used for approved installation. Outlet boxes bind together the elements of a conduit or cable system in a continuously grounded system. They also provide a means of holding conduit in position, along with space and protection for mounted switches and receptacles, and working space for making splices and connections. Boxes can be round, octagonal, square, or rectangular. Commonly used outlet boxes are shown in Figure 10-27.


Figure 10-27 — Typical outlet boxes.

View A — a 4-in. octagon box used for ceiling outlets. This box is made with 1/2- or 3/4-in. knockouts—indentations that can be knocked out to make holes for the admission of conductors and connectors.

View B — a 4 11/16-in. square box used for heavy duty, such as a range or dryer receptacle. It is made with knockouts up to 1 in. in diameter.

View C — a single receptacle gang box used for switches or receptacles. Two or more boxes can be ganged (combined) to install more than one switch or receptacle at a location.

View D — a utility box, called a handy box, made with 1/2- or 3/4-in. knockouts and used principally for open-type work.

View E — a 4-in. square box with 1/2- or 3/4-in. knockouts, used quite often for switch or receptacle installation. It is equipped with plastic rings having flanges of various depths so that the box may be set in plaster walls of various thicknesses.

Besides the boxes shown, special boxes called conduit gang boxes are made to accommodate three, four, five, or six switches.

The NEC® requires outlet boxes be 1 1/2 in. deep except where the use of a box that deep would result in injury to the building structure or is impractical. In such cases, a box not less than 1/2 in. deep may be used. For switch boxes, 2 1/2-in. in depth is the most widely used.

Also per NEC® requirements, outside edges of outlet and switch boxes without flush plates cannot be recessed more than 1/4 in. below the surface of the finished wall.

1.2.9 Receptacles

Receptacles are used to plug in lights and appliances around the building. Figure 10-28 shows some of the most common receptacles


Figure 10-28 — Common receptacles.

A convenience outlet (Figure 10-28, View A) is a duplex receptacle with two vertical or T-slots and a round contact for the ground. This ground is connected to the frame of the receptacle and is grounded to the box by way of screws that secure the receptacle to the box.

A range receptacle (Figure 10-28, View B) may be either a surface type or a flush type. It has two slanted contacts and one vertical contact and is rated at 50 A. Receptacles for clothes dryers are similar but are rated at 30 A. Range and dryer receptacles are rated at 250 V and are used with three-wire, 115/230 V, two hot wires and a neutral.

An air conditioner receptacle taking 230 V (Figure 10-28, View C) is made with two horizontal slots and one round contact for the ground.

Strip receptacles (Figure 10-28, View D) used in the Navy allow movement of the receptacle to any desired location. These strips are available in 3-ft and 6-ft lengths and may be used around the entire room. They are particularly desirable with portable equipment or fixtures such as drafting tables and audio-visual equipment. Exterior locations require special weatherproof outlets to resist weather damage and minimize potential hazards from water contacting the conductors.

1.2.10 Switches

For interior wiring, single-pole, three- or four-way toggle switches are used. Most of the switches will be single-pole, but occasionally a three-way system is installed, and on rare occasions, a four-way system. 

A single-pole switch is a one-blade, on-and-off switch that may be installed singly or in multiples of two or more in a gang box.

In a three-way switch circuit there are two positions, either of which may be used to turn a light ON or OFF.

The typical situation is one in which one switch is at the head of a stairway and the other at the foot.

A four-way switch is an extension of a three-way circuit by the addition of a four-way switch in the line between the two three-way switches. This allows on/off switching from three locations.

Note that three- and four-way switches can be used as single-pole switches, and fourway switches can be used as three-way switches. Some activities may install all smallwattage, four-way switches for all lighting circuits to reduce their inventories.

However, three- and four-way switches are usually larger than single-pole switches and take up more box room. The size of a switch depends on its ampacity (related maximum amperage capacity). The ampacity and maximum allowable voltage are stamped on the switch.

Test Your Knowledge

1. Most power systems use alternating current (ac) because ________.

A. direct current voltage is unstable
B. alternating current is cheaper to produce
C. direct current requires heavier wiring
D. transformers can be used only with ac


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Like mechanical plans, electrical plan information and layout are usually superimposed on the plot plan and the building plan, thus providing common reference points for all the respective trades.

This lesson will address electrical plans pertaining to the electrical (power) distribution system (outside power lines and equipment for multi-building installations) and the interior electrical wiring system.

With electrical drawings, the layout for both light and power is your main concern as an engineering tech, and your tasking may include developing electrical drawings and layouts from notes, sketches, and specifications provided by the designing engineer.

You are not required to design the electrical wiring system, but you must be familiar with symbols, nomenclature, basic functions of components, and installation methods, as well as the transmission, distribution, and circuit hookups associated with the electrical systems.

In addition, you must be familiar with both NEC® and local codes, standards, and specifications, and be able to apply that knowledge in drawing electrical plans.

2.1.0 Standards and Specifications Requirements

Electrical system safety is of prime importance for both personnel and base operations. Consequently, it is imperative that all electrical installations conform to rigid standards and specifications. When preparing construction drawings, engineering techs, must follow the specifications issued by their organization.

In particular, an engineering tech working on electrical wiring and layout diagrams for electrical plans should refer to the latest edition of American National Standards Institute (ANSI) Y32.9 and ANSI Y14.15.

2.1.1 Codes

Installing electrical systems by code requirements and procedures offers protection for the consumer against unskilled electrical labor.

In addition to providing a common standard, the NEC® serves as a basis for limiting the size and type of wiring for specific use, circuit size, outlet spacing, conduit requirements, and other functions. Be certain you always have a copy of the latest edition of the NEC® available. A copy should be maintained in the technical library.

In addition to NEC® standards, local codes are also used when separate electrical sections are applicable to the building locale.

These local codes are similar to NEC® standards for the system wiring in that all of the electrical devices and fixtures that will connect to the wiring (in the electrical plans materials list) must meet certain specifications and minimum requirements.

Underwriters Laboratories (UL) is an independent organization that tests various electrical fixtures and devices to determine if they meet minimum specification and safety requirements as set up by UL. Approved fixtures and devices may then bear UL labels. (Figure 10-29)


Figure 10-29 — Underwriters Laboratory logo.

2.1.2 Permit

Utility drawings (both mechanical and electrical) receive a thorough review before the granting and issuing of an excavation (or digging) permit. This minimizes the hazards to personnel as well as underground utilities, supply lines, and structures during the construction process.

To achieve maximum safety, the reviewing agency must have accurate drawings of existing conditions. As-built and working drawings must note and reflect all minor design changes and field adjustments. Therefore, close coordination and cooperation must develop within and among all of the parties involved in the project. They jointly need to maintain periodic checks on red-lined prints so that they can compare information and verify it as up to date.

2.2.0 Electrical Symbols

There are a myriad of electrical symbols used in schematic drawings, electronics, avionics, shipboard lighting, and so on. The ones you will use as an engineering tech will be limited to those typical of the construction industry. An electrical plan’s symbols indicate general layout, units, related equipment, fixtures and fittings, and the routing and  interconnection of various electrical wiring. Figure 10-30 shows most common types of symbols used in electrical drawings for construction.



Figure 10-30 — Common electrical symbols for construction.

To see additional or special symbols, refer to ANSI Y32.9.

To add electrical symbols on a drawing, as in drawing a mechanical plan, it is best to use templates. For example, a wiring symbol is usually drawn as a single line but it also includes slanting “tick marks” to indicate the number of wires in an electrical circuit.

2.3.0 Exterior Electrical Layout (Plan)

Exterior distribution lines deliver electrical power from a source (generating station or transmission substation) to various points for service drop or service lateral. Figure 10-31 is a typical exterior layout plan, and this condensed layout shows:


Figure 10-31 — Typical exterior electrical layout plan.

As an engineering tech, you may be called upon to trace, modify, revise, and even review the workability of this or similar drawings. Therefore, you need to study and become comfortably familiar with electrical plans.

2.4.0 Interior Electrical Layout (Plan)

The interior electrical layout for a small building is usually drawn into a print of the floor plan. On larger projects, additional separate drawing sheets are necessary to accommodate detailed information needed to meet construction requirements.

Figure 10-32 shows an interior electrical layout of a typical public works shop. Note again that the electrical wiring diagram is superimposed on an architectural floor plan (Lighting circuits use three-wire No. 12 AWG).


Figure 10-32 — Typical interior electrical plan.

The drawing also provides additional specifics needed build this PW shop: a list of assemblies, an electrical load table, and a panel schedule for the 225-A three-phase circuit breaker. The service lateral entrance (item 10 on the list of assemblies) delivers a four-wire, 120/208-V power into the building.

Follow these basic steps as a guide in developing an interior electrical plan. Show:

  1. location of service panel and its rating in amps
  2. all wall and ceiling outlets
  3. all special-purpose outlets such as telephones, communications, doorbells, and so forth
  4. all switches and their outlet connections
  5. all convenience outlets

If required, complete a schedule of electrical fixtures, with symbols, legends, and notes necessary to clarify any special requirements in the drawing that are not stipulated in the specifications. Following these sequential steps will establish good working habits to minimize omissions or errors in your drawings.



This lesson has followed the electrical system from power plant generation through transmission lines to the substation distribution system and on through a service drop or service lateral to the interior of a building for the individual Seabee’s use in a 100 man camp or PWC shop.

As an engineering technician, your tasking is important in providing accurate and timely electrical system information through your drawings for installation, revisions, or as-builts for future reference.

Couple this with your knowledge of mechanical plans and you will soon be able to develop the “Utility” drawings for a project by application of the appropriate symbols for both mechanical and electrical plans.


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Review Questions

1. Which of the following descriptions best defines electrical distribution? A. An electrical transmission system that carries electrical current externally from the generating station via substations and transformers to building locations. B. A power plant that distributes electrical energy by conversion from some other energy source such as wind, geothermal, coal, etc. C. An internal electrical wiring system that distributes electricity to illuminate the building and provide power to appliances and equipment. D. A transmission tower that distributes electrical energy from a substation to a building without a transformer. 2. A complete electrical delivery network is considered a combination of the _____section and the _____section. A. generation, transmission B. transmission, distribution C. transmission, internal wiring D. distribution, internal wiring 3. What type of feeder lines do Builders use at most advance bases? A. Underground cable B. Automatic C. Overhead D. Internal 4. Alternators for a three-wire distribution system are connected in a _____ configuration. A. secondary B. primary C. wye (Y) D. delta 5. A delta connected alternator system has _____ voltage rating(s). A. 1 B. 2 C. 3 D. 4 6. A wye (Y) connected alternator system has _____ voltage rating(s). A 1 B. 2 C. 3 D. 4  10-33 7. What element in a three-wire power distribution system makes it possible to draw 110V from a 220V alternating generator? A. Transformer B. Ground Wire C. Neutral Wire D. Bridge 8. What element in a four-wire power distribution system makes it possible to draw 110V from a 220V alternating generator? A. Transformer B. Ground Wire C. Neutral Wire D. Bridge 9. What type of voltage is required for long-distance transmission? A. Exact voltage from power plant generator B. Voltage higher than normally generated C. Voltage lower than normally generated D. Voltage can be flexible depending on delta or wye (Y) connection 10. What type of transformer is placed between the transmission line and service distribution? A. 220V B. 110V C. Step-up D. Step-down 11. According to Ohm’s law, current varies _____ to _____. A. directly, resistance B. inversely, voltage C. inversely, resistance D. It does not vary 12. Which of the following reasons is NOT an advantage of installing electrical distribution systems underground, rather than overhead? A. Underground installation costs are less. B. Underground lines are secure against high winds. C. Underground lines are less susceptible to enemy attack. D. Underground installation provides open land areas free from distribution systems.  10-34 13. Which underground power distribution system do Builders most frequently install? A. Conduits located in tunnels B. Duct lines C. Cables buried directly D. Tunneled 14. What supplies power from the exterior distribution system to the entry point of the building? A. Panel board B. Switchboard C. Service drop or lateral D. Service entrance 15. What term is used for the starting point for interior wiring? A. Service equipment B. Service conductor C. Service entrance D. Service lateral 16. What amperage does the NEC® recommend for circuit breaker type entrance switches? A. 50A B. 60A C. 100A D. 110A 17. What amperage does the NEC® recommend for individual residences? A. 50A B. 60A C. 100A D. 110A 18. Lighting panels are normally equipped with _____ automatic circuit breakers. A. 15A single pole B. 20A single pole C. 30A paired D. 50A paired  10-35 19. Compared to a No. 4 AWG conductor, the size of a No. 16 AWG conductor is _____. A. smaller B. shorter C. larger D. longer 20. What wire size is most frequently used for interior wiring? A. 8 AWG B. 12 AWG C. 16 AWG D. 18 AWG 21. What is another term for multi-wire conductors? A. Pairs B. Doubles C. Triples with ground D. Cable 22. In which of the following locations is ROMEX NOT authorized for use? A. Embedded in concrete B. Garages C. Storage battery rooms D. All of the above 23. Which of the following types of insulated wire should be used for installation in wet locations? A. RH B. RHW C. RUH D. All of the above 24. A manual conduit bender is called a _____. A. turning tool B. curving tool C. hickey D. turn out 25. Instead of manually making a sharp bend in rigid aluminum conduit, which of the following fittings should you use? A. Coupling B. Conduit union C. Galvanized steel elbow D. Condulet  10-36 26. Which type of PVC conduit is designated for direct earth burial? A. Type I B. Type I R C. Type II D. Type II R 27. Thin-wall conduit _______________. A. must be threaded B. uses a solvent type adhesive weld C. can use rigid conduit fittings D. uses special types of fittings 28. Which of the following boxes would you normally use for a ceiling outlet? A. 4 11/16-in. square heavy duty B. Utility C. 4-in. octagon D. 4-in. square 29. According to NEC® requirements, what is the maximum recess allowed below a finished wall for switch boxes? A. 1/16-inch B. 1/8-inch C. 1/4-inch D. 1/2-inch 30.  If you use the National Electrical Code, NEC®, you do not need to follow local codes. A. True B. False 31. Utility drawings (both mechanical and electrical) are thoroughly reviewed before granting and issuing _____ permits. A. building B. construction C. excavation D. demolition  10-37 32. Which of the following definitions best describes the symbol for a specialpurpose receptacle outlet? A. A circle inscribed in a triangle B. A circle containing a smaller inscribed circle C. A triangle D. A solid triangle inscribed in a circle 33. Which of the following definitions best describes the symbol for a singlepole switch? A. An S B. A circle containing an inscribed S C. A square containing an inscribed S D. A vertically oriented rectangle with a horizontal line on the left 34. Which of the following definitions best describes the symbol for a ceiling outlet? A. A circle B. A circle containing an inscribed C C. A circle with four radiating lines in an X pattern D. A circle containing an inscribed L 35. What NAVFAC publication offers a wide variety of plans, drawings, and applications for use in Seabee Advanced Base Functional Component (ABFC) systems? A. NAVFAC P-307 B. NAVFAC P-405 C. NAVFAC P-437 D. NAVFAC P-300 36.  When drawing exterior or interior electrical plans, you should not superimpose them over site or building plans. A. True B. False