Neutral earthing reactors produced in either air or iron cored versions depending on fault levels and voltage levels required.

An additional advantage of Cressall NERs is that, in contrast to earthing reactors, they do not induce unpredictable phase changes or resonances into the fault current.

It was also suspected that switching surges associated with vacuum circuit breakers (VCB) were adversely interacting with systems that used neutral earthing reactors (NER) as a means of earth fault current limitation.