Generator issue

[JohnE]

Is a generator with a 480/277 Y output allowed to supply a panel supplied with 480 Delta from utility? I'm looking for code articles which would govern installation. The installation is for either a legally or optional standby system. I realize that equipment needs to have proper ratings, etc. It doesn't seem that this should be allowed, but I'm not sure why.

[ July 20, 2005, 09:32 AM: Message edited by: j_erickson ]

 

[bphgravity]

Re: Generator issue

I don't see why not. Do you think the circuits or equipment will know the difference?

 

[rcwilson]

Re: Generator issue

The loads can't tell the difference, but a ground fault can.

If the delta service is ungrounded, the first phase-to-ground fault will not show up on normal power. When power is lost, the transfer switch will start the generator and power the system. Since the generator neutral is grounded, fault current will flow and trip the breaker on the faulted circuit.

IMO, there is no code violation or safety issue. But I would take a look at the emergency loads and think about whether tripping that load during the outage is a good idea.

I have seen similar systems that used high resistance grounding on the generator to alarm on ground faults. This kept power to the critical loads, minimized damage by limiting faults to less than 10 amps and provided a means to trace the faulted circuit.

Bob Wilson

 

[JohnE]

Re: Generator issue

Bob and Bryan,

Thanks for your input. I realize the circuits will not know the difference , Bryan, but I am looking for code compliance. There are numerous code violations in which "the circuits will not know the difference".

John

 

[don_resqcapt19]

Re: Generator issue

There is no code requirement to bond the center of the wye generator. This could be connected as an ungrounded system, just like the utility service.
Don