plug, three-pin

The wiring in an electrical plug. The colours of the wires are used universally to represent the same things: earth is green and yellow, live is brown, and neutral is blue.

A three-pin plug usually contains three wires. The live wire, which is brown, is connected to the pin at the bottom right. The neutral wire, which is blue, is connected to the pin at the bottom left, and the green and yellow earth wire is connected to the central top pin. The wires must be connected to the correct pins.

Insulated device with three metal projections used to connect the wires in the cable of an electrical appliance with the wires of a mains supply socket. In the UK, plugs have pins of rectangular section, and must comply with the British Standard BS 1363 laid down by the British Standards Institute. A plug must be designed carefully with regard to construction, labelling, clearance between components, accessibility of live parts, earthing (see earth), and terminal design. Before being approved, it is tested for the resistance of its insulation, temperature rise while in use, anchorage of cables, mechanical strength, and susceptibility to damage by heat and rust.