Wire and cable: usually twisted by several or several groups of wires [at least two in each group], similar to a rope. Each group of wires is insulated from each other and often twisted around a center, and the whole outer bread is covered with a highly insulated coating. Mostly used for transmission, distribution of electric energy or transmission of electrical signals.

Wires and cables are mainly composed of the following four parts.

1. Conductive wire core: made of high conductivity material (copper or aluminum). According to the requirements of cable flexibility for laying conditions, each core may be twisted by a single conductor or multiple conductors.

2. Insulation layer: The insulation material used for cables should have high insulation resistance. The insulation materials commonly used in cables are oil-impregnated paper, polyvinyl chloride, polyethylene, crosslinked polyethylene, rubber and so on.

3. Sealing sheath: protect the insulated wire core from mechanical, moisture, moisture, chemicals and light damage. For insulation susceptible to moisture, lead or aluminum extrusion sealing sheath is generally used.

4. Protective coating: used to protect the sealing sheath from mechanical damage. Generally, galvanized steel tape, steel wire or copper tape, copper wire, etc. are used as armor wrapped around the sheath (called armored cable), and the armored layer plays the role of shielding electric field and preventing external electromagnetic interference at the same time. In order to avoid the corrosion of steel belts and steel wires by surrounding media, they are generally coated with asphalt or wrapped with impregnated jute layer or extruded with polyethylene and polyvinyl chloride sheath.