If the lighting switch is installed on the zero line, although the light does not turn on when it is off, the phase line of the lamp holder is still connected, and people think that the light is off, they will mistakenly think that it is in a power-off state. In fact, the voltage to ground at each point on the lamp is still a dangerous voltage of 220 volts. If people touch these actually live parts when the light is off, it will cause an electric shock accident. Therefore, the safety of various lighting switches or single-phase small-capacity electrical equipment switches can only be ensured if they are connected in series on the live wire.

2. How to install the single-phase three-hole socket correctly? Why?

　　 Generally, single-phase electrical equipment, especially mobile electrical equipment, should use three-pin plugs and matching three-hole sockets. There is a special protective zero (ground) jack on the three-hole socket. When zero protection is used, some people often only connect the terminal of this hole with the zero wire introduced into the socket directly in the bottom of the socket. This is Extremely dangerous. Because in case the neutral wire of the power supply is disconnected, or the fire (phase) wire and the neutral wire of the power supply are connected reversely, the metal parts such as the shell will also carry the same voltage as the power supply, which will cause electric shock.

　　 Therefore, the dedicated grounding jack should be connected to the dedicated protective grounding wire when wiring. When using zero-connection protection, the zero-connection line should be specially drawn from the power supply end, and the zero-line introduced into the socket should not be used nearby.

　　3. Why is it strictly forbidden to bury the plastic insulated wire directly in the wall?

　　(1) After long-term use of plastic insulated wires, the plastic will age and crack, and the insulation level will be greatly reduced. When the line is overloaded or short-circuited for a short time, it is easier to accelerate the insulation damage.

　　(2) Once the wall is damp, it will cause a large area of electric leakage, endangering personal safety.

　　(3) The plastic insulated wire is buried directly, which is not conducive to line inspection and maintenance.