GFI transfer switch

[drscott]

I have a 3000 amp service that will have a generater installed with it, along with an automatic transfer switch. QUESTION: will the transfer switch need to be gfi protected or will this need to be after the transfer switch? By the way it is a customer owned primary transformer that it is coming off of.
Doug

 

[noxx]

Re: GFI transfer switch

Pretty sure power for emergency equipment (fire pump, shunt, etc) is exempt from the GFI requirement. Per usual my book is down in the truck so probably won't be able to back that up for an hour or two until I get off my duff.

 

[nvcape]

Re: GFI transfer switch

If it is 480/277V, the building main should have GFI, see NEC 230.95. For the generator, see NEC 700.26 and 700.7D. The secondary will be protected by the GFI ahead of it. If this is medical (article 517), there is a lot more to it.

 

[websparky]

Re: GFI transfer switch

What is the KVA of the generator?
What is the voltage?

 

[bwyllie]

Re: GFI transfer switch

is this an existing service with a new generator? with the ATS have OCPD on the normal side? where is the neutral to ground bond for the service?

 

[drscott]

Re: GFI transfer switch

The service will be an upgrade from 800 amps to 3000 amps. new owner moving into building. 277/ 480 volts Generater ? not sure on size yet. Owner still considering cost, but also want backup for the whole service. It's a manufacturing plant, but has critical equipment per power failure.
Doug

 

[steve66]

Re: GFI transfer switch

I would recommend, if possible, dividing the service up into 4 x 800A disconnects. This probably would require multiple transfer switches. But, it eliminates the GFI requirement.

If you are going to back up the entire service, you are talking about 2.5 MVA. That's one big generator. Several smaller generators may be a better idea.

 

[brian john]

Re: GFI transfer switch

Steve:

Depending on they type of OCP, dividing up the service, while NEC approved, is not always a good idea, just to avoid GFP, ONCE AGAIN MY OPINION.

 

[steve66]

Re: GFI transfer switch

Brian: I agree just trying to avoid GFI may not be a good reason to split up the disconnect. But with the generator and GFI, I believe the transfer switches have to be 4 pole with overlapping neutral connections to prevent false tripping.

This sounds like a grounding and bonding headache to me. So I just wanted to be sure Doug was aware that a 3000 amp service doesn't require GFI if the disconnects are all 800A or less.

Steve

 

[hurk27]

Re: GFI transfer switch

I would at least split the critcal equipment off the main service so the gen set could be down sized to power only that which require it. also if this machinery is senative to power loss, a genset will not come on-line fast enough. maybe a UPS would be in order to back up the genset.
Just a thought