Abstract: Transformers (14) inject test voltage signals of know frequency to each phase of the load side of an electrical distribution circuit (15). Processor (32) waits for a delay period to allow transient effects of the injected signals to settle, and then accepts the sampled test current signals provided by current transformers (12) through conditioning circuit (16). This process is repeated by injecting test voltages at different frequencies, which are selected by processor (32) based on stored instructions. Processor (32) uses the sampled signals to determine a representative current for the load side of the distribution circuit (15) and then compares the representative current with a predetermined current threshold value stored in non-volatile memory (40). If the current is above this threshold, processor (32) provides a lockout signal to the fault lockout device (48) and fault lockout flag (50).