Proper NGR Design and Specifications


download "NGR Application and Design" pdf

Neutral Grounding Resistors are similar to fuses in that they do nothing until something in the system goes wrong. Then, like fuses, they protect personnel and equipment from damage. Damage comes from two factors, how long the fault lasts and the fault magnitude. Ground fault relays trip breakers and limit how long a fault lasts based on current. Neutral grounding resistors limit the fault magnitude.

Over the past several years the design and performance standards related to Neutral Grounding Resistors has been updated by IEEE C57.32, CSA 295-2015 and the 2018 Canadian Electrical Code. These changes include the type of resistive element material to use when designing the NGR system as well as the need for continuity monitoring relays.

I-Gard supports all of these changes as they ensure a NGR that is properly designed and will perform its critical function of limiting the maximum fault current to a value which will not damage generating, distribution or other associated equipment in the power system, yet allow sufficient flow of fault current to operate protective relays to clear the fault.