Abstract: A ground fault circuit for a poly-phase circuit is disclosed. The ground fault circuit provides a plurality of current limiting impedance paths from a neutral of the poly-phase circuit to ground. A sensing circuit monitors the paths and may indicate failure of one of the paths. The sensing circuit, may, for example sense the net impedance of the plurality of paths and note an alarm in the event of an increased or decreased impedance, indicative of an open or short circuit along either path.

Abstract: An improved power resistor includes a resistive element extending between a first electrical connection terminal and a second electrical connection terminal. The resistive element has a plurality of first insulating regions, arranged along its length extending generally parallel to each other in a first row. The resistive element further has a plurality of second insulating regions arranged generally parallel to each other in a second row. The first and second rows are further arranged generally parallel to each other so that each of the second insulating regions extends between two of the first insulating regions. The first and second insulating regions thereby define a tortuous current path from the first terminal to the second terminal. This tortuous path creates a current path between the terminals having increased resistance. The insulating regions are preferably interleaved chevrons and are preferably formed by stamping out portions of a resistive slab, made of steel or the like.

Abstract: A fault-current-limiting circuit for a poly-phase circuit of the type including a plurality of inductive windings each of which has a first terminal connected to a common point and at least one of the windings having a second terminal connected to an electrical load is disclosed. The fault-current-limiting circuit has a first electrical path between the common point and ground which includes a current-limiting device having a first state whereat current passes through the device and a second state whereat current through the device is limited and wherein the device switches from the first state to the second state when current through the device exceeds a predetermined maximum and a second electrical path between the common point and ground having an electrical resistance significantly greater than a resistance of the first path when a device is in its first state.