system grounding damaging trip unit?
system grounding damaging trip unit?
(OP)
My client has a dual breaker transfer system utilizing low-voltage air frame power breakers. The alternate (generator source) neutral is bonded at the transfer board. The commercial source feeder breaker in the same board (upstream from the transfer breakers) is equipped with residual ground fault trip. The grounding arrangement is such that ground fault current while operating on the generator source will return through the neutral sensor of the commercial feeder breaker (it could be closed or open). I think this is fairly typical of a non-separately-derived system. I recognize that this could result in unnecessary tripping of the commercial feeder.
The local inspector is insisting this may be harmful to the commercial feeder breaker trip unit and is therefore not allowing it.
I have inquired with the breaker manufacturer and am awaiting a reply. I would be interested to know any opinions.
The local inspector is insisting this may be harmful to the commercial feeder breaker trip unit and is therefore not allowing it.
I have inquired with the breaker manufacturer and am awaiting a reply. I would be interested to know any opinions.






RE: system grounding damaging trip unit?
RE: system grounding damaging trip unit?
RE: system grounding damaging trip unit?
RE: system grounding damaging trip unit?
RE: system grounding damaging trip unit?
RE: system grounding damaging trip unit?
I agree with you that without any doubt the neutral current cannot damage the commercial breaker as the protection works on residual current insensible what current flow through neutral. But if it would be a toroidal CT I think could be a problem. If it will be an outage and the Generator Grounding Protection will fail to operate the problem will be with the cable and not with the breaker. See Attachment
Best Regards
RE: system grounding damaging trip unit?
I have to apologize! There is a 4 conductor distribution then you have to include the neutral too in the residual system. No difference between residual and toroidal. In the extreme case of generator homopolar protection fail the commercial supply cable may be damaged.
Regards
RE: system grounding damaging trip unit?