The motor must have a protective grounding device that meets the requirements. There should be a permanent, reliable and good electrical connection between the motor frame and the protective grounding device. When the motor moves on the equipment base, the protective grounding conductor should still be reliably connected.
Grounding is a critical safety protection requirement for motor products, whether for the motor itself or for operators and related equipment. GB14711 and GB755 are two very important standards for motor products, which provide specific requirements for grounding. However, many motor manufacturers do not handle the grounding of motors properly due to a lack of understanding or other factors.
The standard requires that the motor must have a protective grounding device that meets the regulations. There should be a permanent, reliable and good electrical connection between the motor frame and the protective grounding device. When the motor moves on the equipment base, the protective grounding conductor should still be reliably connected.
In actual production and application, most motor products only have a grounding mark and grounding screw on the motor body, with the grounding wire provided by the customer; however, for motors with long leads, the grounding wire is mostly provided by the motor manufacturer. But due to differences in understanding of grounding wires between suppliers and users, the grounding of some motors is often haphazard, with the grounding wire's color and diameter frequently not meeting requirements. To prevent safety issues, both motor manufacturers and users should strictly adhere to regulations.
Basic requirements for motor grounding protection
● The motor must have a protective grounding device that meets the requirements. There should be a permanent, reliable and good electrical connection between the motor frame and the protective grounding device. When the motor moves on the equipment base, the protective grounding conductor should still be reliably connected.
●If the motor uses a terminal block to connect to the grounding wire, the terminal block must meet the specific requirements. The connection of the protective grounding terminal block should be reliably locked to prevent accidental rotation and to prevent reduction of electrical clearance and creepage distance. It should not be loosened without tools.
●The protective grounding terminal should not be used for any other purpose besides protective grounding.
●The materials of the protective grounding conductor, protective grounding terminal, and their connecting devices should be compatible, resistant to electrolytic corrosion, and be good conductors of electricity. If ferrous metals are used, they should be electroplated or other effective measures should be taken to prevent corrosion.
●The protective grounding conductor should have sufficient toughness to withstand the vibration stress of the motor, and appropriate protective measures should be taken to prevent danger during the use and installation of the motor.
● The protective grounding connection should ensure reliable penetration through non-conductive coatings such as paint. The connection method can be cold pressing or other equivalent means; hinged connections and soldering alone should not be used.
● The grounding electrode that penetrates the elastic rubber base should be metal; conductive rubber cannot be used for grounding.
●The screws and grounding conductors of the protective grounding terminal should have sufficient cross-section. The minimum diameter of the protective grounding screw is specified in Table 1.
● The cross-sectional area of the grounding conductor should meet the requirements, and the specific values are shown in Table 2.
For other phase conductor cross-sectional areas, the cross-sectional area of the grounding conductor or protective conductor should not be less than:
(1) When the cross-sectional area of the phase line is less than 25 mm2, it is the cross-sectional area of the same phase line.
(2) When the cross-sectional area of the phase wire is (25~50) mm2, it is 25 mm2.
(3) When the phase wire cross-sectional area is greater than 50 mm2, it is 50% of the phase wire cross-sectional area.
● The resistance of the grounding path should not exceed 0.1Ω .
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