Neutral Grounding Resistors are an effective way to limit fault current in industrial power distribution systems. The proper application of a neutral grounding resistor is the result of a complete evaluation of the system design and capabilities and an evaluation of fault current of the system. It is the responsibility of the specifying engineer to properly evaluate the system parameters and determine the equipment to meet the system design requirements. Neutral Grounding Resistors are in short known as NGR’s and and hence we will be using the term NGR frequently hereafter..

Applications:

Essen make NGR’s are installed in series with the power system neutral grounding connection. By inserting our NGR’s one can limit the ground fault current and the damages which may result from a system phase to ground fault. The NGR is provided with a termination for the power system neutral and the opposite side is connected directly to a suitable ground. In some cases the NGR may actually be wired to the secondary of a single phase transformer which has its primary wired in series with the power system neutral to ground connection. The ratio of the transformer will “reflect” the resistor’s impedance into the power system neutral bonding connection. Essen make NGR’s also incorporate an earth fault CT which is placed in the neutral connection at this point to operate protective relaying systems. In most cases the current transformer primary will be the same rating as the resistor i.e. a 600 amp resistor will have a 600:5 current transformer