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A power cable is an assembly of one 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. ==History== Early telegraph systems used the first forms of electrical cabling, transmitting tiny amounts of power. Gutta-percha insulation used on the first submarine cables was, however, unsuitable for building wiring use since it deteriorated rapidly when exposed to air. 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.〔"undergrounding electric lines" A J Pansini, ISBN 0-8104-0827-9, 1978〕 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.〔''Underground Systems Reference Book'', Edison Electric Institute, New York, 1957, no ISBN〕 Rubber-insulated cable was used for 11,000 volt circuits in 1897 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.〔R. M. Black The History of Electric Wires and Cables, Peter Pergrinus, London 1983 ISBN 0-86341-001-4〕 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〔http://www.thisoldhouse.com/toh/article/0,,562098-12,00.html〕 - introduced in 1906 but more expensive * Rubber-insulated wires with jackets of woven cotton cloth (usually impregnated with tar), waxed paper filler - introduced in 1922 * Early two-wire PVC-insulated cable, known by the genericized trademark "Romex", 〔 1950s * Aluminum wire was used in the 1960s and 1970s as a cheap replacement for copper, but this is now considered unsafe due to corrosion〔http://www.thisoldhouse.com/toh/article/0,,562098-8,00.html〕 * Asbestos was used as an Insulator (electricity) in some cloth wires from the 1920s to 1970s. * Modern three-wire PVC-insulated cable, also known as "Romex" - see thermoplastic-sheathed cable 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Power cable」の詳細全文を読む スポンサード リンク
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