Earth Fault and Overcurrent Relay

Hello

But it SHOULD trip on earth fault.

Maybe the relay is just overloaded?

Find and fix the earth fault. If the relay is tripping on earth fault then the sum of the earth leakages from all the devices connected to the relay exceeds its trip curve. Either that or you have a faulty piece of equipment that is shorted to ground.

With so little information its hard to give more detailed advice. If this is an industrial application with variable speed drives or other electronic control devices with large capacitors then the capacitor leakage can cause the earth fault relay to trip during either power up or normal operation. If the earth fault problem just started then it could be a single bad variable speed drive with a leaky capacitor, or a faulty piece of equipment shorted to ground.

Yep. Find and eliminate the earth fault that is causing the breaker to trip, preferably before some anus bypasses it and someone gets hurt/maimed/killed.

Could you give some information as below

1. What is the voltage level, what is the upstream source is it star winding of a delta star transformer etc

2. What is the load. is it motor or distribution circuit etc and howmany wires (three phase with neutral single phase etc)

3. Is it earth fault and over current relay, or just earth fault relay etc.

4. Is the earth fault element connected from the three CTs or from a core balance CT.

5. Atlast what is the typical condition when it trips?

Hopefully with above we can get more deep in to the subject.