If it is found that there is an AC power supply greater than 5 volts on the zero line of the ground wire, it can basically be concluded that the ground wire is ungrounded or poorly grounded, or some grounding equipment has too serious leakage;
The voltage between live wire and neutral wire is 220V, that between live wire and ground wire is 220V, and that between neutral wire and ground wire is 0V.
Two wires in the lighting circuit, one is called live wire and the other is called zero wire. The difference between live wire and neutral wire lies in their different voltages to ground: the voltage of live wire to ground is 220 V; The voltage of neutral line to ground is equal to zero (it is itself grounded). Therefore, when one part of a person touches the fire line and the other part stands on the ground, the voltage between these two parts of the person is equal to 220V, and there is a danger of electric shock; Instead, people grab the zero line with their hands. If a person is standing on the ground, the voltage between the neutral line and the ground is equal to zero, and the voltage between all parts of the human body is equal to zero, so there is no danger of electric shock.