A wire is composed of one or several flexible wires, wrapped with a light and soft protective layer; BV and RV wires are commonly used, among which BV copper core polyvinyl chloride insulated wires have a long-term allowable temperature of 70 ℃, a minimum temperature of -15 ℃, and a working voltage of 500V AC and 1000V DC. They are fixed and installed indoors and outdoors, and can be exposed or concealed. RV - PVC insulated single core flexible wire, with a maximum operating temperature of 90 ℃ and a minimum operating temperature of -15 ℃. It operates at AC 250V and DC 500V, and is used for internal wiring of instruments and equipment.