Abstract: This report analyzed the cause of the fan motor burnout through macroscopic, microscopic, and metallographic test methods to find out the root cause. The simulation verification was used to analyze the cause of burnout and replicate the burnout process. The results showed that the root cause of the primary short circuited of the copper wire was the existence of cracks on the surface of the copper wire. When the motor was running at high speed, the fatigue propagation of the crack caused the wire cross- sectional area to decrease. Excessive instantaneous current during startup caused high temperature fusing of the copper wire. After the copper wires fused, the fuse end was stuck between the rotor and the stator of the motor after stopping. When restarting, the motor could not rotate due to the low starting torque and was overloaded and eventually burned.

Key words: motor, primary fuse, fire investigation