Fluxgate sensors measure magnetic fields by periodically saturating a piece of ferromagnetic core material in alternating directions. When an external magnetic field is present, the periodic saturation is offset and measured. Intrinsic magnetic noise from the core as the core saturates limits fluxgate performance.

A ground fault creates a magnetic field due to the imbalance of current through line and return current through neutral.

Current going through a wire creates magnetic fields. When equal current flows in opposite directions, the sum of magnetic fields cancels out. To detect milliampere (mA) levels of fault current, use a soft magnetic material that has a high permittivity and low coercivity. The Hitachi core used for this design is FT-3K70T F2520C which is a nanocrystalline core. The core is wound with two sets of 100 and turns a 34-gauge magnet wire. Magnetics CMC020012008h is another nanocrystalline core option.