Function
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The purpose of the service drop and the service entrance is to get electricity safely from the utility into your house.
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Overhead Wires To House
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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.
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Underground Wires
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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.
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Drip Loop
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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. The drip loop is typically 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. The drip loop 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 may just be a cable. They may be above the roof or below it, attached to the house wall.
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Old Systems
Connections To The Roof
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Some old service drops do not have a drip loop. In warm climates, the service wires 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 are then susceptible to pulling out of the rotted wood.
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Responsibilities
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The utility usually provides the service drop and the homeowner is responsible for the service entrance, including the drip loop. The utility may be responsible for maintaining the service drop wires.
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Often Smaller Wires Than Service Entrance Wires
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It is incorrect to use the service drop wires to gauge the size of the electrical service. These wires are very often smaller than the service entrance wires and will mislead you. These wires are in open air and can carry more electricity because it’s so 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.
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Usually Three Wires In Service Drop
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The number of wires coming in through the service drop will tell you some things about the house service. There will usually be three wires coming in through the service drop: a black, a red and a white (neutral). Sometimes the neutral is also the support cable for the red and black. Sometimes 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.
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240 Volts
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Are there three wires spliced into the service entrance? If so, this will be a typical 240-volt, single-phase residential service.
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Two Wires For 120-volt Services
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Two wires spliced into the service entrance cable indicate a 120-volt service. This is rare and not adequate for most modern lifestyles.
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Four Wires Mean 3-Phase Service (Commercial)
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Four wires coming into the house indicate a three-phase system. This is a commercial electrical system. Three-phase services are rare in single family residences.
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Underground Wires
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Where the service is underground (service laterals) you can’t see very 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 is usually some slack created at the point of connection to the building to allow for frost heaving or building settlement.
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Maybe In Conduit
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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 future.
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Conduit On Vertical Only
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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 conduit bottom so the cable doesn’t get cut.
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No Service Entrance Wires
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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.
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