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.
Flexible power cables are used for portable devices, mobile tools and machinery.
Higher voltages
For circuits operating at or above 2,000 volts between conductors, a conductive shield may surround each insulated conductor. This equalizes electrical stress on the cable insulation. This technique was patented by Martin Hochstadter in 1916;the shield is sometimes called a Hochstadter shield. The individual conductor shields of a cable are connected to earth ground at the ends of the cable, and at locations along the length if voltage rise during faults would be dangerous.
Cables for power distribution of 10kV or higher may be insulated with oil and paper, and are run in a rigid steel pipe, semi-rigid aluminum or lead sheath. For higher voltages the oil may be kept under pressure to prevent formation of voids that would allow partial discharges within the cable insulation.
A high voltage cable designed for 400 kv. Large center conductor carries the current, smaller conductors on the outside act as a shield to equalize the voltage stress in the thick polyethylene insulation layer.
Modern high voltage cables use polymers or polyethylene, including (XLPE) for insulation. They require special techniques for jointing and terminating, see High voltage cable.
Many multiconductor cables have a bare or insulated grounding or bonding wire which is for connection to earth ground. The grounding conductor connects equipment enclosures to ground for protection from electric shock.
Electrical power cables are often installed in raceways, including electrical conduit and cable trays, which may contain one or more conductors.
A hybrid cable can include conductors for control signals or may also include optical fibers for data.
Flexible cables
All electrical cables are somewhat flexible, allowing them to be shipped to installation sites wound on reels or drums. Where applications require a cable to be moved repeatedly, such as for portable equipment, more flexible cables called "cords" or "flex" are used. Flexible cords contain fine stranded conductors, not solid core conductors, and have insulation and sheaths to withstand the forces of repeated flexing and abrasion. Heavy duty flexible power cords such as those feeding a mine face cutting machine are carefully engineered — their life is measured in weeks. Very flexible power cables are used in automated machinery, robotics, and machine tools. See power cord and extension cable for further description of flexible power cables. Other types of flexible cable include twisted pair, extensible, coaxial, shielded, and communication cable.
X-ray cable is a special type of flexible high voltage cable.