A cable is usually a rope-like cable consisting of several or groups of conductors [at least two] strands, each of which is insulated from each other and often twisted around a center, and the entire outer bread has a highly insulated covering layer. Installed in the air or underground, underwater, for telecommunications or power transmission.

In 1832, the Russian military officer Schuellinger buried the Telegraph line in the ground, six the wires between each other with rubber insulation and placed in the glass tube, this is the world's first underground cable. An insulated conductor consisting of one or more insulated conductive wire cores placed in a sealing sheath. The outer layer can be protected to transmit, distribute or transmit electrical signals.

The difference between it and the ordinary wire is mainly the cable size is larger, the structure is more complex. The cable is mainly composed of the following 4 parts. ① Conductive Core: made of high conductivity material (copper or aluminum). According to the requirements of laying conditions for the softness of the cable, each core may be stranded by a single conductor or multiple conductors. ② insulation: Insulating material used as a cable should have high insulation resistance, high breakdown electric field strength, low dielectric loss and low dielectric constant. The insulating materials commonly used in cable are oil-impregnated paper, polyvinyl chloride, polyethylene, XLPE, rubber and so on. Cables are often classified by insulating materials such as oil-impregnated paper insulated cables, PVC cables, XLPE cables, etc. ③ Seal sheath: Protects the insulated wire from damage caused by mechanical, moisture, moisture, chemicals, light, etc. For moisture-prone insulation, the general use of lead or aluminum extrusion sealing sheath. ④ Protection cover: protects the seal sheath from mechanical damage. The general use of galvanized steel, steel wire or copper tape, copper wire, etc. as armor wrapped around the sheath (called Armored cable), armored layer at the same time from the electric field shielding and prevent external electromagnetic interference. In order to avoid the steel belt, the steel wire is affected by the surrounding medium corrosion, generally on their outside coated with asphalt or wrap around the impregnated jute layer or extruded polyethylene, PVC sleeve.