Abstract: In response to a failure of an operation board in a motor protection device, this paper analyzes the on-site phenomena of KKJ relay damage and abnormal closing operations. Through an analysis of the operation board circuit principle, the temperature characteristics of the current-limiting resistors, and the on-site application mode, it is revealed that the root cause of the failure lies in the long-term energization of the manual closing/tripping circuits, which are originally designed to operate in a short-time pulse mode. Prolonged energization causes the relay coils and resistors to be continuously subjected to excessive thermal stress, thereby accelerating aging and eventual failure. Based on this analysis, measures such as prohibiting long-term energization, optimizing circuit structure, and improving parameter design are proposed, providing references for the design and field application of similar operation circuits.