Source: Alliance of Electrical Experts
Original name: Which electrical equipment must be grounded? Which does not need to be grounded? Many people don't know a lot
When it comes to grounding, it is estimated that most electrical personnel are no strangers. With the rapid development of science and technology, the application of electrical equipment is more and more extensive, in order to improve the reliability of the operation of electrical equipment, it is necessary to connect a certain point of the live part of the electrical device or electrical circuit with the earth, and the artificial connection between a certain point of the uncharged part of the electrical device or other devices and the earth is called grounding; The grounded part of the power system is generally a neutral point, or it can be a certain point on the phase line, and the grounding part of the electrical equipment is a metal conductor that is not charged under normal circumstances, and is generally a metal shell. Grounding of electrical equipment is an important measure to prevent the occurrence of electrical accidents. So electrical equipment: which must be grounded, which ones do not need to be grounded? Let's take a look!
In order to ensure the safety of maintenance personnel, the electrical equipment in the power plant and substation must be grounded.
1. Bases and shells of motors, transformers, electrical appliances, lighting appliances, portable and mobile electrical appliances, etc.
2. The control mechanism of electrical equipment.
3. The secondary winding of the instrument transformer.
4. The frame of the distribution box and control box.
5. Metal frame and reinforced concrete frame of indoor and outdoor power distribution devices and metal near the live part.
6. Metal ends, sheaths and threading steel pipes of AC and DC power cables.
7. In the residents of non-asphalt ground, the metal towers and concrete towers of the overhead power system of the small current grounding system without lightning wires, as well as the power line towers with lightning lines.
8. Electrical equipment installed on the distribution line structure.
The following electrical equipment does not need to be grounded:
1. Electrical equipment mounted on a grounded metal frame.
2. The metal shell of measuring instruments, relays and low-voltage electrical appliances installed on distribution boxes, control boxes and distribution devices, etc., and the metal base of insulators.
3. Control the outer sheath of the cable and the metal bracket of the battery room with a voltage of 220V or less.
4. In dry places, the shell of electrical equipment with AC voltage of 127V and below, DC voltage of 110V and below.
5. In a dry room with non-conductive floor, the electrical equipment shell with an AC voltage of 380V or less and a DC voltage of 440V or less, except when the staff may touch the equipment shell and grounding objects.
6. Railway tracks in the area of power plants and substations.
7. Motors and electrical appliances that have reliable electrical contact with the grounded machine base.
Summary: Some people always think that all metal live equipment needs to be grounded, and it is good to have a sense of self-protection, but some equipment is not actually necessary to be grounded, such as the metal shell of the instrument in the distribution box and control box.