A power cable is an electrical cable used specifically for transmission of electrical power. It is an assembly of one or more electrical conductors, usually held together in a single bundle with an insulating sheath, although some power cables are simply rigged as exposed live wires. Power cables may be detachable portable cords (typically coupled with adaptors), or installed as permanent wirings within buildings and structures, buried in the ground, laid underwater or run overhead. Power cables that are bundled inside thermoplastic sheathing and that are intended to be run inside a building are known as NM-B (nonmetallic sheathed building cable). Small flexible power cables are used for electrical devices such as computers and peripherals, mobile devices, home appliances, light fixtures, power tools and machinery, as well as household lighting, heating, air conditioning and rooftop photovoltaic and home energy storage systems. Larger power cables are used for transmission of grid electricity to supply industrial, commercial and residential demands, as well as a significant portion of mass transit and freight transport (particularly rail transport).
History The first power distribution system developed by Thomas Edison in 1882 in New York City used copper rods, wrapped in jute and placed in rigid pipes filled with a bituminous compound. Although vulcanized rubber had been patented by Charles Goodyear in 1844, it was not applied to cable insulation until the 1880s, when it was used for lighting circuits. In 1897, rubber-insulated cable was used for 11,000-volt circuits that were installed for the Niagara Falls power project. Mass-impregnated paper-insulated medium-voltage cables were commercially practical by 1895. During World War II, several varieties of synthetic rubber and polyethylene insulation were applied to cables. Typical residential and office construction in North America has gone through several technologies:
Early bare and cloth-covered wires installed with staples Knob and tube wiring, 1880s–1930s, using asphalt-saturated cloth or later rubber insulation Armored cable, known by the genericized trademark "BX" – flexible steel sheath with two cloth-covered, rubber-insulated conductors – introduced in 1906 but more expensive than open single conductors Rubber-insulated wires with jackets of woven cotton cloth (usually impregnated with tar), waxed paper filler – introduced in 1922 Modern two or three-wire+ground PVC-insulated cable (e.g., NM-B), produced by such brands as Romex Aluminum wire was used in the 1960s and 1970s as a cheap replacement for copper and is still used today, but this is now considered unsafe without proper installation, due to corrosion, softness and creeping of connection. Asbestos was used as an electrical insulator in some cloth wires from the 1920s to 1970s, but discontinued due to its health risk. Teck cable, a PVC-sheathed armored cable
Construction Modern power cables come in a variety of sizes, materials, and types, each particularly adapted to its uses. Large single insulated conductors are also sometimes called power cables in the industry. Cables consist of three major components: conductors, insulation, and a protective jacket or sheath. The makeup of individual cables varies according to application. The construction and material are determined by three main factors:
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