480/277 vac utility / 480/277 generator at transfer swit

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watsons

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My question is in regards to 480 vac delta utility feed to a 3 pole transfer switch which is then fed to a 480 delta/208 wye transformer as well to a 480 vac a/c unit. Is the neutral required from both sources (generator and utility)to the switch if there are no single phase loads? Is a Ground rod needed in this non separately derived system?

"Update"
What I have is a 480/277 using just 3 wires with with a ground which is brought to a 480/277 distribution panel with a ground only. At this time there is only 3 phase loads with no neutral. Is it required to bring the neutral in from the generator as well as the utility since it is a wye configuration with no single phase loads? I would not think so but common since and courtesy for future expansion would be to bring the neutral in. As far as the grounding electrode from what I am reading in the old NEC 99, I am unable to see where it actually sais that an electrode is NOT required for a non separately dervived system.

SORRY FOR THE MISLEADING POSTING FROM THOSE WHO READ IT PREVIOUSLY!!

[ February 27, 2006, 10:23 AM: Message edited by: watsons ]
 
Re: 480/277 vac utility / 480/277 generator at transfer swit

I don't understand where you will get a neutral if the utility provides you with a delta service.

Did you just run 3 wires or is it a true delta?

If it's a delta is it ungrounded, or corner grounded?

Jim T
 
Re: 480/277 vac utility / 480/277 generator at transfer swit

It sounds like you are deriving a neutral from the transformer which means that at least the load side of the transformer is a SDS.
 
Re: 480/277 vac utility / 480/277 generator at transfer swit

If there is a "neutral" which is really a grounded conductor supplied by the utility it must be brought to the service entrance equipment where it is bonded per 250.24(C). If Your generator is a wye connected SDS then see 250.30.
 
Re: 480/277 vac utility / 480/277 generator at transfer swit

From your PM, it sounds like you have an ungrounded delta from the utility and a 277/480 volt generator on the emergency side.

The question then becomes, does the generator have to be grounded, and the neutral and ground brought to the ATS or not?

Am I close to understanding your installation configuration?

Jim T
 
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