Abstract: A method of detecting absence of connection of an external ground to a ground connection point associated with an AC supply circuit of a power supply. The AC supply circuit has hot and neutral conductors, with the neutral conductor externally connected to ground. The math involves (a) passing a current from the hot conductor to the neutral conductor via the ground connection point, (b) detecting passage of the current, (c) shutting down operation of the power supply upon detection of the current, and (d) bypassing at least an effective portion of the current from the ground connection point to external ground on connection of the ground connection point to external ground, thereby disabling the detection of passage of the current.

Abstract: A ground fault circuit comprising: a power supply, and a transformer having a primary winding driven by the power supply and a high voltage secondary winding, a shutdown control circuit having a controllable switch and a control input coupled to the controllable switch for causing operation of the controllable switch when a trigger voltage applied to the control input is exceeded, the shutdown control circuit being coupled to the power supply for controlling shut-down of the power supply when the switch is in operation, a circuit connected to the high voltage secondary winding for detecting leakage current from the transformer to ground, for short circuiting an A.C. component of the leakage current passing through the detector to ground, and for deriving a D.C. voltage from D.C. leakage current from the transformer to ground, and a circuit for applying the derived D.C.