Ground Fault protection
Ground Fault protection
(OP)
In a 3 wire grounded system, if the main breaker has a ground fault function, the CT's common will need to be connected to ground terminal of the relay.
I know that in this case the sum of three currents will pass to ground and create a signal to activate the relay.
How the setting and coordination would be done in this case?
The other question is if the arc fault current is calculated from %38 of 3phase bolted current or LG bolted current?
Thanks
I know that in this case the sum of three currents will pass to ground and create a signal to activate the relay.
How the setting and coordination would be done in this case?
The other question is if the arc fault current is calculated from %38 of 3phase bolted current or LG bolted current?
Thanks






RE: Ground Fault protection
If possible, the ground relay should be set to coordinate (grade) with upstream/downstream ground protection (or, depending on grounding arrangement, phase overcurrent protection if no other ground overcurrent protection exists).
RE: Ground Fault protection
The issues are co-ordination with other ground fault devices upstrem and down stream, and nuisance tripping.
As an example, a system may have more than 20,000 amps available short circuit current, a main breaker of 1200 amps and a ground fault setting of 5 or 10 amps.
Within the limits of co-ordination and nuisance tripping, lower is better.
respectfully