Cable, in electrical and electronic systems, a conductor or group of conductors for transmitting electric power or telecommunication signals from one place to another. Electric communication cables transmit voice messages, computer data, and visual images via electrical signals to telephones, wired radios, computers, teleprinters, facsimile machines, and televisions. There is no clear distinction between an electric wire and an electric cable. Usually the former refers to a single, solid metallic conductor, with or without insulation, while the latter refers to a stranded conductor or to an assembly of insulated conductors. With fibre-optic cables, made of flexible fibres of glass and plastic, electrical signals are converted to light pulses for the transmission of audio, video, and computer data.
Fibre-Optic Telecommunication Cables
Cables made of optical fibres first came into operation in the mid-1970s. In a fibre-optic cable, light signals are transmitted through thin fibres of plastic or glass from light-emitting diodes or semiconductor lasers by means of internal reflection. The advantages of fibre-optic cables over conventional coaxial cables include low material cost, high transmission capacity, low signal attenuation, data security, chemical stability, and immunity from electromagnetic interference.
Like other types of cables, fibre-optic cables are designed and insulated for various applications overland, underground, overhead, and underwater. Such cables usually consist of a core embedded in a series of protective layers. The cable core contains a single solid or stranded central strength element that is surrounded by optical fibres; these are either arranged loosely in a rigid core tube or packed tightly into a cushioned, flexible outer jacket.
The number and type of protective layers surrounding the core depends upon the use for which the cable is intended. In general, the core is covered with a layer of copper to improve conduction over long distances, followed by a material (e.g., aluminum foil) to block the passage of water into the fibres. Steel wire or strands are added for tensile strength, and the entire cable is then wrapped in a polyethylene sheath, or jacket, for stability. See also fibre optics.
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