【 Weak current College 】 safe use of electricity and lightning-building--the second section of the electrical equipment protection measures

This section describes the electrical equipment have a short, leakage and unexpected touches the human body charged body protective measures. 　　Through study, should understand the grounding protection, zero leakage protection and automatic cutting works. A, ground protection protective earthing, the power equipment, metal shell and grounding, the use of power equipment and Earth closely connected. In power for three-phase three-wire grounding neutral does not direct or single-phase system power system should be set to protect Earth wire.　　If the residual current device has already been adopted-grounding protection, fault current will be through circulation through the grounding of the human body all the current is only part of the ground currents.　　In power for three-phase four-wire neutral earthing transformers of power system, if you simply take protective grounding, when a phase occurs with shell short-circuit, human and protection earthing devices in parallel, with the voltage on the human body is equal to the voltage drop resistance, usually ranging from 110V, the voltage on the human body is very dangerous. Second, zero protection protection zeroing is electrical equipment under normal circumstances no live metal parts and the grid of the zero line closely connected. In power for three phase and four wire transformers neutral power system direct grounding should be protected from zero.　　Zero protection power zero line equipment, which prompted the formation of single-circuit protection device on the line rapid action to cut off the power. In the three-phase four-wire system power system, do not allow only for certain devices take zero, on others only take protective grounding and not zero. The correct method is to repeat the grounding protection device, that is, zero line on one or more through the Earth and Earth connect again. Usually the electrical equipment of the metal shell while grounding and zero.　　You should also note that the zero line circuit does not allow installation of fuses and switches. Third, leakage protection installed earth leakage protection device's main role is to prevent electric shock due to leakage caused by personal, followed by the prevent leakage caused by equipment fire, as well as surveillance, one touches the ground after power failure. The protector can cut three-phase motor dephased failure.