Is the electrical equipment protective earthing is not live metal parts with good metal connection between the grounding to protect human security. If it does not have a protective grounding of electrical equipment, when somewhere in the insulation of electrical equipment is damaged, it shouldn't have charged parts of it may charge, likely to cause electric shock.
Protective earthing device is connected when the body when touching live parts, due to the resistance of human body is approximately 1000 ω, and resistance is only 10 ω, both parallel and almost zero current through the human body, thus avoiding the occurrence of electric shock accident. In the industrial circuits, suitable protective earthing of neutral point not grounding of three-phase four-wire system.
Protection circuits of 0 refers to the industry, the electrical device is not a charged metal parts connected with the zero line in the system, in order to avoid human suffering risk of electric shock. Protect electrical equipment zero when insulation damage, shell when charged, short circuit current zero-line formation pathways, quick and reliable protection equipment, disconnect the device.
In practical use, protection of zeroing has more advantages than the ground. When a short occurs, cut off the electricity because the phase line with neutral short-circuit impedance between the small, short circuit current, protective devices and agility. Protection zero for neutral-point earthing in low voltage three-phase four-wire system.