The Neutral Grounding Reactor is a single-phase reactor in three-phase power system and Connected between the neutral and earth of transformer to limit the fault current.

Neutral-earthing reactors are also used for reducing momentary over voltages during breaking of instantaneous fault current.

Under normal system conditions, voltage across a neutral-earthing reactor is small. Consequently, the current through the reactor is also small.

During system fault, current will increase considerably and its duration in seconds must be specified. Insulation requirements of an NGR correspond to the insulation of the neutral of the power system or the shunt reactor in which the reactor is to be installed. For earth terminal, selection of a reduced insulation level may be appropriate (non-uniform insulation).