The ground fault current caused by ground neutral wire fault is low, the induction coil is difficult to detect, and depends on the impedance of ground neutral wire. To detect the fault, apply the forward feedback principle. When this happens, the induction and neutral coils are coupled bidirectionally, creating a positive feedback path around the induction amplifier. This forward feedback causes the induction amplifier to resonate. When the peak resonance voltage exceeds the comparator trigger threshold, the built-in delay timer will be started. Since the amplifier output can cross the trigger threshold voltage of the window comparator and the frequency is typically 6kHz, the delay timer switches between fault and trouble-free detection. The ratio of failure to fail-free detection times will determine whether the SCR drive is enabled or not. (The sensitivity of ground neutral wire detection varies with the number of turns of neutral wire coil and the values of C2 and C3)

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