A power cable is an assembly of two or more electrical conductors, usually held together with an overall sheath. The assembly is used for transmission of electrical power. Power cables may be installed as permanent wiring within buildings, buried in the ground, run overhead, or exposed.
Medium and high-voltage power cables, in circuits over 2000 volts, will have a shield layer of copper or aluminum tape or conducting polymer. If an unshielded insulated cable is in contact with earth or a grounded object, the electrostatic field around the conductor will be concentrated, resulting in corona discharge, and eventual destruction of the insulation. As well, leakage current and capacitive current through the insulation presents a danger of electrical shock on contact. The grounded shield equalizes electrical stress around the conductor, diverts any leakage current to ground, and blocks capacitive current from flowing into objects (or persons) touching the exterior of the cable.