1. Regulations for grounding resistance of large grounding current systems (grounding current above 500A):

In a large ground current system, when a single-phase short circuit occurs, the ground short-circuit current is very large, and the corresponding relay protection quickly removes the fault. Therefore, overvoltage appears on the grounding device for a short period of time, and the staff touches the device at this time The chance of the enclosure is very small. Considering that the ground current of this system is generally greater than 4000A, the grounding voltage should not exceed 2000V and the grounding resistance should not exceed 0.5Ω.

2. Regulations for ground resistance of small ground current systems (ground current below 500A):

When single-phase grounding occurs in a small ground current system, it is allowed to continue to run for a period of time (usually 2h). Therefore, it is more likely that workers will touch the shell of live equipment. Since its ground current is relatively small, the ground voltage regulations are also low. The regulations stipulate: the grounding device shared by high and low voltage devices, the grounding voltage shall not exceed 120V. The grounding device used alone for the high-voltage device, the grounding voltage is not more than 250V. In general, the grounding resistance should not be greater than 10Ω.