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Cable is a kind of electric energy or signal transmission device, which usually consists of several wires or groups of wires. It is usually a rope-like cable twisted by several or several groups of steel wires (at least two in each group). 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 insulating coating. The cable has the characteristics of internal electrification and external insulation. Cables include power cables, control cables, compensation cables, shielded cables, high-temperature cables, computer cables, signal cables, coaxial cables, fire-resistant cables, marine cables, mining cables and aluminum cables. Are composed of single or multiple wires and insulation layers, used to connect circuits, electrical appliances, etc.