Power Solutions

What Is a Neutral Grounding Resistor (NGR) and Why Every Site Needs One

Ground faults happen — insulation ages, moisture gets in, equipment shifts. What determines whether a ground fault is a minor event or a major failure is how the system's neutral point is grounded. A Neutral Grounding Resistor (NGR) is one of the most effective and widely used ways to control that outcome.

What an NGR Does

An NGR is connected between a transformer's or generator's neutral point and ground. When a ground fault occurs, it limits the fault current to a controlled, predictable level instead of allowing it to spike to near-unlimited magnitude, as can happen in a solidly grounded or ungrounded system.

Why This Matters

	Equipment protection Limiting fault current reduces mechanical and thermal stress on transformers, generators, and cabling during a fault.
	Safer fault detection A controlled fault current makes it possible to detect and clear faults reliably without nuisance tripping.
	Reduced arc flash risk Lower fault current means less energy released during a fault, lowering arc flash hazard for personnel.
	Continued operation options In some configurations, resistance grounding allows a system to keep running briefly during a single ground fault, avoiding an unplanned full shutdown.

Sizing matters: An NGR has to be sized to the specific system voltage, transformer capacity, and protection scheme in use. An incorrectly sized resistor can either fail to protect equipment or interfere with fault detection.

Not sure if your site's grounding setup is adequate? Germarel can help assess your system and specify the right NGR for your application.