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This post was last edited by It will be more tomorrow_bZzMU on 2020-2-2 at 15:26. To prevent damage to the protective insulation layer of the motor windings, which could lead to leakage and electric shock, it is necessary to provide the motor with a protective grounding or safety neutral connection system in order to ensure personal safety. When electric motors are connected to a three-phase power supply, if the grid neutral point is not directly grounded, these motors should be provided with protective grounding. The method involves connecting the motor housing to the ground wire; generally, thicker multi-strand copper wires (with a cross-sectional area of not less than 4 mm2) are used to establish a reliable connection to the grounding electrode. This method is known as protective grounding, and the grounding resistance should generally be no more than 4 Ω. The principle is as follows: once a leakage occurs in the motor, when a person touches the motor’s casing or when leakage takes place through metal conduits to other metal components, since the resistance of the human body is much higher than that of the ground, the leakage current flows mainly into the ground via the grounding system. This prevents the human body from being subjected to a high current that could be fatal, thereby ensuring personal safety. Where conditions permit, such as when the grid neutral point is directly grounded, protective earthing measures can be adopted. The specific method is to connect the metal casing of electrical equipment (such as the casing of a motor) to the neutral wire of a three-phase four-wire power supply using copper wires. This type of safety measure is relatively safe and reliable; in the event of leakage from the electrical enclosure, it quickly generates a high short-circuit current that melts the fuses in the electrical equipment or causes overcurrent protection devices such as circuit breakers to trip, thereby cutting off the power supply and protecting human safety. It must be noted that, in the same three-phase four-wire system, it is not allowed for the enclosures of some motors equipped with star-delta starting devices to be protected by grounding, while the enclosures of other electrical equipment are protected by protective neutral connection. The grounding electrodes used for installing grounding devices can be made of thicker metal materials such as steel pipes, angle iron, or copper pipes. The wall thickness of the steel pipes should be at least 3.5 mm, and their length is preferably around 2.5 meters. The grounding electrodes should be buried vertically in the ground, with their upper surface being at a depth of no less than 0.6–0.8 meters, as shown in the figure below. To facilitate penetration into the ground, the tip of the grounding electrode should be pointed. To reduce the ground resistance, the number of grounding electrodes should be three or more; it is best to bury them underground in a triangular pattern and connect them together (to form a grounding electrode assembly). Add some resistance reducers around them, or a mixture of table salt and charcoal, and finally protect the area around the grounding electrode to prevent pedestrians from touching it. http://www.weijizongbao.com/d/file/ebca162f19c43745c232796b8149c6f0.jpg