Neutral Earthing Resistors (or NGR) are a key component in earth fault protection of medium voltage electricity generation and distribution systems.

Nepean NERs limit the current that would flow through the neutral point of a transformer or generator in the event of an earth fault. For the majority of ratings the most suitable element type is Nickel-Chromium Stainless Steel AISI430.

Nepean resistors are manufactured from a continuous stainless steel strip, (or wire depending on rating) wound into oval coils. Each coil is supported by ridged ceramic insulators with stainless steel terminals welded at each end. This arrangement allows free expansion and contraction at operating temperatures up to 1100°C without imposing strain on the assembly.

The resistance alloys used are high temperature stainless steels capable of withstanding temperature excursions to 1100°C whilst retaining their strength, unlike 304 or other structural grade stainless steels which are limited to much lower temperatures.

NERs designed for operation to higher temperatures require less active mass, resulting in more compact and economical designs.