An electric service drop is the bundle of electrical cables that run from the electric utility company's power pole to the connection at your house. Because the power company lines are higher than your home, the cables that go to your home literally drop, descending from a higher spot to a lower spot. If your home does not have a service drop, it is supplied by similar cables running underground.
Service Drops Provide All Power
All electricity to your home comes through the service drop. If the service drop goes down, all power in your home will shut off. Catastrophic events, such as downed trees, large fallen limbs, or heavy ice buildup, can take down a service drop. Fallen service drops are extremely dangerous, since they carry enough electricity to power an entire house. Do not approach a fallen service drop.
A standard service drop includes three cables, or conductors. Two are insulated "hot" cables, each carrying 120 volts of electricity. A third cable, usually bare (uninsulated) aluminum, serves as the neutral conductor and provides structural support for the entire service drop.
Service Drops vs. Buried Power Lines
While overhead service drops were the standard for many years, more recent housing construction favors underground service lines. When the lines are underground, they are referred to as a service lateral rather than a service drop. Buried lines are preferred primarily because they are not vulnerable to falling trees, high wind, and other destructive effects of weather. The lines are also out of view and eliminate the danger of accidental contact with ladders or vehicles.
On the downside, underground service lines are at risk of being struck by construction crews or possibly even homeowners digging in their yards. Installing and repairing buried lines is much more costly and labor-intensive than with overhead service drops, and underground lines and related equipment can be affected by shifting ground.
The Service Head and Service Point
When the service drop reaches the house, it connects to an assembly called the service head, also know as the service mast or masthead. Typically, a service head consists of a rigid steel conduit (like a big pipe) that runs up through the roof or along an exterior wall and is topped with a shell-like fitting called a weatherhead or weather cap.
The open front of the weatherhead faces downward to keep out rain and snow. The bottom end of the service mast connects to the home's service panel, or breaker box. An additional set of service cables starts at the service panel (and the electric meter) and runs up through and out of the service head. These cables connect to the service drop cables near the outside of the mast. This connection is called the service point, and it represents the dividing line between the utility company's property and the homeowner's property (although the meter may be owned by the utility even though it is on the homeowner's side).
The Drip Loop
Near the service point, the service cables make a downward loop, known as the drip loop. This is a simple system that uses gravity to prevent water from running down the cables and into the service head. Beads of water traveling down the outside of the cables collect at the bottom of the loop, where they eventually drop off of the cable.
Service Drop Height Requirements
Minimum height requirements for service drop cables are determined by the local building or electrical codes, but most follow the recommendations of the National Electrical Code (NEC). In general, a service drop must be at least 12 feet above the ground (grade) as well as sidewalks and residential driveways. Minimum height above areas accessible only to pedestrians, such as porches or decks, is 10 feet. Minimum distance above a swimming pool is 22 1/2 feet. When service drops are suspended above public roads, they must be at least 18 feet high.
Service Drop Repairs
While homeowners in many municipalities are allowed to do their own electrical work, this applies to household projects, like replacing outlets and lights, running electrical cable, and maybe even installing new circuits. However, homeowners are not allowed to work on any part of the utility's service drop. For one thing, the service drop belongs to the utility company, not to the homeowner. For another, power in the service drop cables can be shut off only by the utility company.
Homeowners also should not attempt any work on the cables between the service drop and the home's electrical service panel. As with the service drop, power in these cables also is live at all times unless the power company shuts it off. If you have a problem with the service drop supplying your home, call the utility company. If you have a problem with the service head or the cables between the service point and your home's service panel, call a licensed electrician.