Abstract: Based on the current research and judgment methods for small current grounding faults of inside and outside substations, this paper analyzes the commonly used detection principles and related technical requirements for small current grounding faults in primary and secondary fusion switches. It provides a detailed introduction to the acceptance method and grounding fault handling plan for small current grounding protection of primary and secondary fusion equipment. Finally, taking a company in a certain city in Jiangsu as an example, the effectiveness of on-site application of primary and secondary fusion switches is illustrated, and the current terminal issues are pointed out.