Neutral Earthing Resistor (NER)
Technically, it is a bank of resistor elements made of stainless steel covered by a metal enclosure. It is connected between the Neutral of a power source and the Earth grid.
(NER) is also known as a Neutral Grounding Resistor (NGR), is a safety device used in electrical power systems to limit the current that flows during a ground fault.
Without NER, a fault where a power line touches the ground (ground fault) could create a massive uncontrolled surge. This surge can melt copper windings, cause explosions in switchgear and pose a lethal risk to personnel.
NER primary functions are:
1- Limiting Fault Current:
It acts like a brake restricting a potential 20 kA fault down to a manageable level, such as 50A or 400A.
2- Protection for Relays:
By allowing a small and controlled amount of current to flow, it gives protection relays a clear signal to see the fault and trip the circuit breaker.
3- Reducing Arc Flash:
It significantly lowers the energy released during a fault, reducing the risk of fire and explosive arc flashes