Most older homes have an overhead electrical service connection, where the primary power arrives from the utility company's power lines from a transformer mounted on the power pole high above a street or alley. This overhead power line running to the house is called a service drop, and building codes require that the overhead wires be at least 12 feet above the driveway or yard. The point of attachment to a house's service connection must be a minimum of 10 feet above the ground.
The Components of the Service Drop
The service drop is connected to the electrical service entrance wires via a service assembly that is usually attached to the side of your house. The service assembly consists of an electric meter and electric meter base that is attached to a vertical pipe, or service mast, fitted with a rounded piece known as the weather head, which covers the electrical wires run up the mast and connecting to the utility company's service drop. If you observe how the wires enter the weather head, you will notice that they droop in a downward loop. This is the part of the system known as the drip loop, and it exists so that rainwater and moisture gathering on the wires will flow downward and drip off the bottom of the loop rather down through the service mast toward the electrical meter.
Note: many overhead services don't use a mast, but rather simply run a cable up from the meter base to the location where the service drop attaches to the house. There is still a weather head made to fit on the cable versus the type that attach to the mast.
The Drip Loop
The term "drip loop" refers to this downward-facing, half-moon loop formed by the incoming feeder wires of the electrical service, just before they enter the weather head that sits atop the service mast. The electrical service consists of three wires—two black hot wires, each delivering 120 volts of hot current, and a white neutral wire or, in the case of service entrance cable, a bare neutral wire. There is also a support cable running from the service mast to utility pole, around which the service wires are wrapped in a spiral fashion. When the utility company runs the service wires, they are careful to provide some excess wire—generally 2 to 4 feet—so the two hot wires and the neutral wire can be positioned with a drip loop at the weather head.
The drip loop functions by simple gravity. If rainwater or other moisture collects on the service wires, it naturally flows down to the bottom of the loop, where it drips harmlessly to the ground, rather than down into the service mast.
A drip loop can be a feature of other wiring systems as well, such as low voltage wiring or cable TV entry wires. It is a method used wherever there is a need to control the flow of rainwater. If you are running this wire yourself, make sure to leave plenty of excess wire—2 to 4 feet—so that a drip loop can be properly formed.
If the Drip Loop Is Missing
In the unfortunate event that you are without drip loops on your service wiring, a simple phone call to the utility company to explain the situation may be all it takes to prompt a quick visit from a service crew to fix the situation. Utility companies are generally very eager to fix this problem in order to avoid complicated damage in the future.
Be proactive and get the crews out to fix the problem now, not when you are actually having problems with the electrical service. Water that drips down past the weather head and through the service mast can cause very serious problems to a home's electrical system, and just because you haven't experienced problems thus far does not mean you're not begging trouble for the future. Even in very dry climates where there is little rainfall, occasional dew or frost can cause moisture to flow down into the service mast and cause damage unless there is a drip loop to prevent it.