Abstract: A circuit tests the health of a ground-neutral transformer within a ground fault circuit interrupter. This test can include testing both the ground-to-neutral detection circuitry and the differential current detection circuitry. The test circuit provides a conductive path through the respective cores of a differential transformer and the ground-neutral transformer of the GFCI device. A closed loop induces current from the differential transformer, which creates a current imbalance through the differential transformer. In a properly working device, the circuit breaker will trip, confirming the health of the ground-neutral transformer portion of the GFCI.