The I-Gard SIGMA Monitoring Relay is a combination Neutral Grounding Resistor (NGR) monitor and ground fault relay. In distribution systems employing Resistance Grounding the SIGMA Monitoring Relay protects against ground faults and abnormal conditions in the path between system neutral and ground possibly caused by loose or improper connections, corrosion, foreign objects or missing or compromised ground wires.
 
The SIGMA Monitoring Relay measures the current through the NFR, the transformer neutral-to-ground voltage and the NGR resistance. The relay compares the measured values against the field settings of the relay and provides relay outputs and LED indications when an abnormal condition is detected.

Combination Ground Fault Relay and NGR Monitoring Relay

MODBUS communication available

Indicates failure if NGR circuit is opened or shorted.