Abstract: Novel apparatus and method accurately measure ground circuit impedance. A ground circuit and electrical current source adjusted to 25 amperes or less simulate a ground fault. Ground impedance is determined by dividing voltage drop by amperage to determine impedance directly. In one aspect, impedance is determined and displayed automatically. Power wires of the circuit being measured serve as a means for transmitting voltage and current data. The cable itself serves as a current-carrying and voltage-transmitting conduit to determine directly the circuit impedance. The novel ground circuit impedance device and method measure impedance in underground mine power systems connecting to an outside electrical power substation outside the mine and using portable transformers in the mine.