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. Fiber-optic cable began to be replace earlier forms of undersea cable in the 1980s. The importance of undersea cable has grown enormously with the development of the Internet, and more than 700,000 mi (1.1 million km) of undersea cable is now in use.

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.

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