An arc suppression coil is a single phase, variable inductance, oil immersed, iron core reactor that is connected between the neutral of a transformer and ground for the purpose of achieving a resonant neutral ground. The zero sequence impedance of transformer is taken into consideration in rating the inductance of the arc suppression coil. The adjustment of the inductance is achieved in steps by means of taps on the winding or can be continuously adjusted by varying the reluctance of the magnetic circuit; the length of the air gap is adjusted by means of a central movable portion of the core.