Service drop

A service drop is an electrical line running from a utility pole to a customer's house. When these lines are insulated and twisted together, they are referred to as a triplex cable.

Usually, a service drop is made up of two 120 volt lines and a neutral line. These lines enter the customer's house by first passing through an electric meter, and then entering the main service panel. The service panel will usually contain a "main" fuse or circuit breaker, which controls all of the electrical current entering the building at once, and a number of smaller fuses/breakers, which will protect individual circuits.

Since the service drop provides the building with two separate 120 volt lines, circuits of both 120 volts (which power most lights and appliances) and 240 volts (which power high-power devices, such as air conditioners, clothes dryers, and boilers, to name a few examples) are possible. A 120 volt circuit will be connected to the neutral line and either of the two 120 volt lines; a 240 volt circuit will be connected to both 120 volt lines, with no neutral connection.

The above description applies to residential service in the United States (and perhaps other parts of North America). In much of the world, residential service is a single phase at 200–240 volts.

Commercial and industrial service drops can be much bigger, and are usually three phase. In the USA, common services are 120Y/208 (three 120V circults 120 degrees out of phase, with 208V line to line), 240V three phase, and 480V three phase. 575V three phase is common in Canada, and 380-415V or 690V three phase is found in many other countries. Generally, higher voltages are used for heavy industrial loads, and lower voltages for commercial applications.