Cable, Electric

Cable, Electric, cable composed of one or more electric conductors, covered by insulation and sometimes a protective sheath, used for transmitting electric power or the impulses of an electric communications system.

For electric-power transmission, three-wire cables sheathed with lead and filled with oil under pressure are employed for high-voltage circuits; secondary distribution lines usually employ insulated single-conductor cables. In residential electric wiring, B-X cable is often used. This type of cable contains two insulated conductors, which are wound with additional layers of insulation and covered with a helically wound strip of metal for protection. The ignition cable used to carry high-voltage current to the spark plugs of an internal-combustion engine is a single-conductor cable; it is covered with cloth impregnated with shellac for insulation.

In communications systems, cables commonly consist of numerous pairs of paper-insulated wire, encased in a lead sheath; the individual pairs of wire are intertwined to minimize induced interference with other circuits in the same cable. To avoid electrical interference from external circuits, cables used in radio broadcasting are often shielded with a winding of metal braid, which is grounded. The development of the coaxial cable was an important advance in the communications field. This type of cable consists of several copper tubes; each tube contains a wire conductor that extends along its centre. The entire cable is sheathed in lead and is generally filled with nitrogen under pressure to prevent corrosion. Because the coaxial cable has a broad frequency range, it is valuable in the transmission of carrier-current telephony (see Telephone) and television.

See also Fibre Optics; Wire.