Under service a transformer

[Dan Kissel]

I have a 500 Kva 240 to 480 step up transformer that I want to reuse on a 240 unground delta service but I don't have the 1200 amp circuit breaker that would provide full service to transformer's low side. Schneider Electric's lead time for material is ridiculous so I am stuck trying to use a smaller circuit breaker for now.
I may have a 1200 amp breaker but do I need to have the ground fault and ERMS switch installed on the 1200 amp service, which is why I am trying to avoid the full 1200 amp.

 

[electrofelon]

I have a 500 Kva 240 to 480 step up transformer that I want to reuse on a 240 unground delta service but I don't have the 1200 amp circuit breaker that would provide full service to transformer's low side. Schneider Electric's lead time for material is ridiculous so I am stuck trying to use a smaller circuit breaker for now.
I may have a 1200 amp breaker but do I need to have the ground fault and ERMS switch installed on the 1200 amp service, which is why I am trying to avoid the full 1200 amp.

Couple things. You need to to keep starting the transformer in mind. Ideally you would have transformer inrush information and can compare with the trip curve of your breakers. If it's not something that is turned on and off frequently and you have people who know what they're doing who can reset it if it trips after a power outage then that might not be it a big concern for you to have a setup where it won't hold on startup on occasion.

Just a tip if you having trouble with availability check some of the online breaker places like Pacific Coast breaker, super breakers etc.

I'm not following the concern about the ground fault, are you talking about the 480 side? That ocpd will be well under a thousand amps.

 

[Elect117]

I believe ground fault protection of equipment is specific to wye grounded systems (240.13) and ERMS can be installed on a fused disconnect.

240.67 & 240.87.

 

[electrofelon]

I believe ground fault protection of equipment is specific to wye grounded systems (240.13) and ERMS can be installed on a fused disconnect.

240.67 & 240.87.

Check the voltage requirements in 240.13, that would not apply. Sounds like 240.67 would not apply. I agree with you 240.87 WOULD apply. IF you want to avoid 240.87 I believe you would be stuck with a max 1000A breaker which will likely prove problematic for starting.