Current through a wire produces a magnetic field. Explained in Detection Principals section, a ground fault produces a magnetic field. Average voltage across the fluxgate burden resistor changes proportional to the ground fault magnetic field. This average voltage is filtered and read to determine if there is a ground fault.

The core is driven into saturation with a driver circuit. Once reaching saturation, the driver circuit switches the direction of the current until the core reaches saturation again. The drive circuit continuously switches the drive current direction every time the core reaches saturation. Prior to saturation, the ambient field is channeled through the core producing a high flux due to the high permeability. At the point of saturation, the core permeability falls away to the vacuum. During the next half cycle of excitation drive current, the core recovers from saturation, and the flux due to the ambient field is once again at a high level until the core saturates in the opposite direction; the cycle then repeats.