Abstract: A ground fault and over-voltage detector and method is disclosed for sensing a loss of neutral continuity between the respective neutral conductors of a ground power unit and an aircraft power system coupled to the unit. The detector includes a feedback path for carrying a feedback signal from the aircraft to the ground power unit. The feedback signal comprises a voltage signal referenced to the aircraft neutral and includes a ground fault voltage component. The detector further includes a signal conditioner disposed in the ground power unit for receiving the feedback signal and generating a signal representative of the magnitude of the ground fault voltage component. A comparator connected to the output of the signal conditioner contrasts the ground fault voltage magnitude signal to a predetermined threshold and a cutoff mechanism responsive to the comparator, when the ground fault voltage is greater than the threshold, to interrupt ground power from the ground power unit to the aircraft.