Besides switches, sockets represent the most important products of all manufacturers of switches. The socket serves as an electrical connector between lines. It is either permanently installed on a wall (surface-mounted socket) or recessed (flush-mounted socket). But sockets can also be part of a mobile line coupling, such as table or multiple sockets. In addition, sockets are found at extension cables that are designed for mobile use. An electrical outlet is mostly used for power supply, but there are also sockets for telephone / telecommunications and data transmission. Typically, electrical outlets supply devices with single-phase AC (230 volts) or three-phase alternating current (AC 400 volts). Furthermore, there are standardized sockets for 12V DC. To provide higher voltages and currents there are extra special socket systems.