A service conductor is the wire or set of wires that transmit electricity from a transformer on a distribution line to a customer facility. Service conductors have different names depending upon their location or type.
When run overhead, the service conductor is called a service drop or service drop conductor. When run underground, the service conductor is called a service lateral.
For overhead service, the service transformer is mounted on a pole near the customer and the service drop conductor carries power at the service voltage. The type of conductors that are used for overhead single-phase service are typically aluminum triplex cable. Notice in the illustration below that a triplex cable has three wires: two insulated wires (the phase conductors) and an uninsulated neutral or ground wire.
For three-phase overhead service quadraplex is typically run. Quadraplex is very similar to triplex except there are four wires, three of which are insulated corresponding to the three phases in the three-phase system and again the bare or ground wire.
For underground service, the conductors are run below ground from the pole or pad-mounted transformer to the meter enclosure. If underground service is provided from an above-ground system, a riser runs down the pole to contain the conductor that then goes underground. The service transformer may be located on the pole, in which case the conductor going down the pole would carry power at service voltages, or the transformer may be a pad-mount transformer located near the pole. In this case, the conductor going down the pole will carry power at primary voltages to the transformer. The service lateral running from the transformer to the customer meter will be at service voltage.
If service is provided from an underground system, a transformer may be pad-mounted or may be placed in a vault. When placed underground, a service conductor is called a service lateral or simply a service. Depending on the type of service, cables may be directly buried or may be run through a conduit. Directly buried conductors are made from specially manufactured and insulated cables that provide protection from moisture and corrosion. Often the individual insulated wires are packaged in a solid plastic covering, creating a prepackaged conductor called an Underground Service Entrance or USE cable. USE cable can be directly buried in the soil. The alternative is to run regular triplex or quadraplex cable in a conduit underground.