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cable

cable originally wire cordage of great strength or heavy metal chain used for hauling, towing, supporting the roadway of a suspension bridge, or securing a large ship to its anchor or mooring. Today a cable often refers to a line used for the transmission of electrical signals. One type of electric cable consists of a core protected by twisted wire strands and suitably insulated, especially when it is used to cross oceans undersea; a message transmitted by cable is known as a cablegram or cable. France and England were first successfully connected by submarine telegraphic cable in 1845. The first permanent transatlantic cable was laid in 1866 by Cyrus West Field , although demonstrations of its possibility had been made in 1858. The first telephone message was transmitted from New York to Philadelphia in 1936; the first transatlantic telephone cable was laid in 1956.

The coaxial cable, which is virtually immune to external interference, consists of two concentric conductors separated by an insulator; the current in the inner conductor draws the current in the outer conductor toward the center rather than letting it dissipate outwards. Because they can carry a large number of signals simultaneously, coaxial cables are also used in cable television systems. The newest form of cable is the fiber-optic cable, developed in the 1970s. Instead of a copper conductor, a silica glass fiber carries digitized signals as pulses of light.

The insulated wire that conducts electricity from generator to consumer is also called a cable; it often contains multiple conductors and must be of sufficient gauge to carry large currents. Its insulation must withstand high voltages.