Most of the power sockets we use are single-phase three-wire sockets or single-phase two-wire sockets. Single-phase three-wire socket, with grounding wire in the middle, is also used for positioning. The other two ends are connected with live wire and zero wire respectively, and the wiring sequence is left zero and right fire, that is, the zero wire is on the left.

The three plugs are arranged in a diamond shape, and the longest and thickest copper plug on the top is the ground wire. The grounding wire is short-circuited with the earth through the deep buried electrode.

The transmission of commercial power is a three-phase mode with a neutral line. When the three phases are in balance, the current of the neutral line is zero, commonly known as the "zero line". Another characteristic of the neutral wire is that it is short-circuited with the ground wire at the input end of the total distribution of the system, and the voltage difference is close to zero.

The voltage of three-phase line and neutral line of three-phase electricity is 220, which will cause electric shock to people. Find out that the zero line is directly connected to the N hole of the socket three holes. Find the E hole where the ground wire is directly connected to the three holes of the socket.