Iron conduit impedance effects in ground circuit systems

THE resistance and reactance of a circuit increases when associated with an iron conduit. In normal circuit operation where the current-carrying conductors are wholly within a conduit, the iron has little effect on the resistance and reactance since the magnetic field locally surrounding the conductors is partly in iron and mostly in air. However, the circuits encountered in building wiring during a phase-to-ground fault condition that involves the conduit in and around the faulted circuit are subject to an appreciable increase in resistance and reactance. The purpose of this paper is to record a relatively simple method of approximating the impedance of such a faulted circuit, to point out the significance of the impedance values as they occur in practice and why these values must be considered by the engineer in design of circuits, particularly under faulted conditions.