Abstract: When a C-phase ground fault occurred on a 10 kV feeder line, the arc suppression device switchgear operating on the same 10 kV busbar tripped due to the mismatch between the current transformer wiring method and the protection device setting. The paper analyzes the case from the aspects of the structure of the on-site arc extinguishing device, message analysis of the accident process, fault waveform recording, and setting of the fixed value, and proposes solutions.