OVERHEAD SERVICES

Overhead and underground entrance systems are the conductors and the equipment used for the control and protection of electrical circuits, equipment, and personnel. The SE is the end of the interior electrical system. This lesson will teach you how to describe an overhead entrance system.

The conductors from the power pole to the building are called service drops as shown in Figure 1. The minimum height of a service drop above the ground and on the building is determined by its location.

Figure 1-1. Clearances for a service drop.
Figure 1. Clearances for a service drop.

Above foot-traffic areas, 10 feet of vertical clearance is necessary for service drops supported and wrapped on a ground messenger having 150 volts to ground between the current-carrying conductors (Figure 2). Remember, the 10-foot minimum clearance is measured from the lowest point of the SE cable. 

Figure 1-2. Service drop above a foot-traffic area.
Figure 2. Service drop above a foot-traffic area.

Above residential property, driveways, and areas not subject to truck traffic, 12 feet of vertical clearance is maintained for conductors having 300 volts to ground (Figure 3).

Figure 1-3. Service drop above residential property not subject to truck traffic (300 volts to ground).
Figure 3. Service drop above residential property not subject to truck traffic (300 volts to ground).

Above residential property, driveways, and commercial property not subject to truck traffic, 15 feet of vertical clearance is maintained for conductors having 600 volts to ground (Figure 4). Automobiles and small vehicles can clear an SE cable with a minimum clearance of 15 feet to ground.


Figure 4. Service drop above residential property not subject to truck traffic (600 volts to ground).

Above public streets and parking areas subject to truck traffic, 18 feet of vertical clearance is required in Figure 5. A 20-foot-high load did not clear the service drop.

Figure 1-5.  A high load damaging a service drop.
Figure 5. A high load damaging a service drop.

Above a peaked roof, having a 1:3 pitch or more, an 18-inch vertical clearance is necessary when the voltage between conductors is less than 300 volts and the SE is a mast within 48 inches of the roofs edge (Figure 6).

Figure 1-6. Clearance between the roof and the service drop (300 volts).
Figure 6. Clearance between the roof and the service drop (300 volts).

Conductors that carry more than 300 volts require an 8-foot vertical clearance (Figure 7).

Figure 1-7.  Clearance between the roof and the service drop (300 volts).
Figure 7. Clearance between the roof and the service drop (300 volts).

Conductors that are installed at the side of a window or below it must have a 3-foot clearance (Figure 8).

Figure 1-8. Conductor clearance from windows.
Figure 8. Conductor clearance from windows.

For fire escapes, porches, or platforms, conductors must have 3 feet of horizontal clearance from the object and 10 feet of vertical clearance from the ground (Figures 1-9 and 1-10). 

Figure 1-9. Fire escape/platform clearance.
Figure 9. Fire escape/platform clearance.

Figure 1-10.  Clearance above ground level.
Figure 10. Clearance above ground level.