1. The three-phase four-wire system is used to transmit power in the low-voltage power grid. Among them, three phase wires (live wires) represent the three phases of A, B, and C, and one is the neutral wire N (zero wire). In order to ensure the safety of electricity use, the power supply in the user area is changed to a three-phase five-wire system. The fifth wire is the grounding protection wire PE (earth wire), one end of which is buried in the ground with a metal conductor near the user area , The other end is connected to the ground contact of each user, which plays a role of grounding protection.

2. The ground wire is a line that reliably connects the casing of the equipment or electrical appliances to the earth, and is a good plan to prevent electric shock accidents. Correct grounding can improve the anti-interference ability of the entire system.

3. Most of the power sockets we use are single-phase three-wire sockets or single-phase two-wire sockets.