The purpose of the service drop and the service entrance is to get electricity safely from the utility into the house.
Overhead wires to house
The service drop is the collection of overhead wires coming from the utility pole (often at the street) to the point of connection to the house. People call these the overhead wires or overhead service. Electricians and utilities use the words service drop.
Some utilities use the word service laterals to refer to underground services. Here, the wires come from the street underground to the house. They may come up out of the ground outside the house to go to an outside meter or they may go straight into the house.
Where the service drop or service lateral ends, there is a splice, sometimes called the service point. This means two wires are joined together. In a service drop, this will be at the drip loop. The drip loop is a U-shaped bend in the wires that allows water to drip off so it won't go into the service entrance. Typically, it is part of the service entrance and is the responsibility of the homeowner. The loop is not part of the service drop. The drip loop also shows that the wires are properly secured to the building and are relaxed. It is at the top of the masthead (also called service cap, entrance cap, pothead, weatherhead or servicehead). The wires running from this connection down into the service box are called the service entrance. The wires may be in a conduit or just may be a cable. They may be above the roof or below it, attached to the house wall.
Some old service drops do not have a drip loop. In warm climates, the service wires sometimes were fastened directly to the roof surface rather than to a service mast. This is not a good arrangement because it makes roofing repair and re-roofing difficult. It also creates potential roof leaks. If leaks occur at these connectors, the wood roof structure may rot in this area. The wire connectors then are susceptible to pulling out of the rotted wood.
The utility usually provides the service drop and the homeowner is responsible for the service entrance, including the drip loop.
Inspect from the roof? Careful!
You have to decide whether you are going to get on the roof. Doing so gives you a better look, although please, resist the temptation to touch these wires. Electrical systems can look perfectly safe but be very dangerous.
Photo: The splices at the two insulated wires should not be bare.
Often smaller wires than service entrance wires
Some home inspectors use the service drop wires to gauge the size of the electrical service. These wires often are smaller than the service entrance wires and will mislead you. They are in open air; therefore, they can carry more electricity because it's easy for them to dissipate their heat. The wire sizes and ampacities that we normally use are for wires in conduit or cable, not for service drop wires.
Usually three wires in service drop
The number of wires coming in through the service drop will tell you some things about the house service. Usually, there will be three wires coming in through the service drop: two hot wires and a neutral wire. Sometimes, the neutral also is the support cable for hot wires. Other times, there is a separate cable supporting the three conductors. The neutral wire may be bare (no insulation) and in some cases is smaller than the hot wires.
240 volts and two wires for 120-volt services
Are there three wires spliced into the service entrance? If so, this will be a typical 240-volt, single-phase residential service. Two wires spliced into the service entrance cable indicate a 120-volt service. This is rare and not adequate for most modern lifestyles.
Four wires mean 3-phase service (commercial)
Four wires coming into the house indicate a three-phase system. This is a commercial electrical system and beyond the scope of a standard home inspection. Most home inspectors cannot competently inspect a three-phase system and will call for a specialist to help. Three-phase services are rare in single-family residences.
Where the service is underground (service laterals), you can't see much. The wires should be buried at least 24 inches. In some areas, where they go below driveways or parking areas, they have to be buried 3 feet. There usually is some slack created at the point of connection to the building to allow for frost heaving or building settlement.
May be in conduit
The cable may be buried directly or may be in a conduit. Burying the cable in an oversized conduit allows easy replacement or upgrading of the service in the future. The cable may enter a conduit that runs up the outside of the building to the above-grade meter. Again, you can't see the connections from the cable into the conduit, but there should be a bushing on the conduitbottom so the cable doesn't get cut.
No service entrance wires
The underground service laterals may head straight into the house to the main disconnect. In this case, there are no service entrance conductors as such.
Here are some of the service drop problems you'll find:
- Overhead wires too low
- Damaged or frayed wires
- Trees or vines interfering with wires
- Wires too close to doors or windows
- Wires not well secured to the house
- Poor connection between the service drop and service entrance
- Inadequate clearance from roofs
- Service lateral problemsa
These problems, and their associated causes, implications and strategies for inspection, are discussed in detail in the ASHI@HOME training program.
Image: The service drop wires should not be in contact with the metal gutters and the roof.
This article is from the ASHI@Home education system, developed by Carson Dunlop with ASHI. Individual modules are approved for ASHI CE credits. Choose the printed version or the online learning program. Call 800-268-7070, Ext. 251, to learn more.