Abstract: This paper focuses on the selection of neutral grounding resistance and the setting of leakage protection in the 660 V distribution system of large coal plants. It systematically analyzes the relationship between neutral grounding resistance and arc grounding over-voltage and single-phase grounding fault current. By combining the actual operation data coal preparation plants, an estimation method for the leakage current of the 660 V distribution system in normal operation is proposed. On this basis, with the goal of ensuring the and reliable operation of the system, a reasonable value range for the neutral grounding resistance and a setting scheme for the leakage protection device are proposed. The results of the study show the selection of neutral grounding resistance needs to take into account the dual requirements of suppressing arc over-voltage and limiting fault current. At the same time, the setting value of protection should avoid the normal leakage current of the system to ensure the accuracy and sensitivity of the protection device.The research in this paper provides feasible reference basis for the design and construction commissioning of 660 V power distribution system in large coal preparation plants.