ATS- 4 or 3 Poles?

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faresos

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I have an application where we have 1000A service at 480/277V and a 130KW generator. The generator is powering a fire pump (75HP) with service rated ATS and in addition we have another ATS (150A) is powering a standby loads. My question is does the standby ATS needs to be a 4-poles since we have the main service (1000A breaker) is protecetd by GFI breaker? or the rule is if the breaker feeding the ATS is GFI then it needs to be 4-poles?

Any thoughts will be appreciated.
Thanks,
 
faresos said:
I have an application where we have 1000A service at 480/277V and a 130KW generator. The generator is powering a fire pump (75HP) with service rated ATS and in addition we have another ATS (150A) is powering a standby loads. My question is does the standby ATS needs to be a 4-poles since we have the main service (1000A breaker) is protecetd by GFI breaker? or the rule is if the breaker feeding the ATS is GFI then it needs to be 4-poles?

Any thoughts will be appreciated.
Thanks,
Click to expand...
How do you intend to run the grounding conductor and the neutral? At the generator is the neutral going to be bonded to the grounding conductor?
It is of my opinion that the neutral is to be grounded to the grounding conductor at one point only, either at the service entrance or the genset and if so a 4p ATS would be used to switch the neutral such that it's grounded at the source that is providing power.
If the neutral is to remain on insulated and isolated from the grounding conductor at the genset and only grounded at the service entrance then a 3p switch would be used.
As such it all depends upon what your intent would be regarding the point of which the neutral is grounded.
On small portable gensets the neutral is often grounded to the frame and as such the neutral and grounding conductor are bonded together there. This poses an issue when connecting that genset to supply emergency power to a home.where attention must be paid to prevent the neutral conductor from being bonded at both the sevice entrance and at the genset.
I've sold many ATSs of many sizes and 3p application were much more common.
 
The neutral and the equipment grounding conductor will be bonded only at the main service. The reason of the question some engineer made a comment stating that since the main service is protected by GFP breaker then a 4-pole ATS is needed so the GFP work properly.
 
faresos said:
The neutral and the equipment grounding conductor will be bonded only at the main service. The reason of the question some engineer made a comment stating that since the main service is protected by GFP breaker then a 4-pole ATS is needed so the GFP work properly.
Click to expand...

Cummins Power has a great white paper on this subject. Part 1:https://www.cumminspower.com/www/literature/technicalpapers/PT-6005-GroundingAC-1-en.pdf
and Part 2:https://www.cumminspower.com/www/literature/technicalpapers/PT-6006-GroundingAC-2-en.pdf
 
faresos said:
The neutral and the equipment grounding conductor will be bonded only at the main service. The reason of the question some engineer made a comment stating that since the main service is protected by GFP breaker then a 4-pole ATS is needed so the GFP work properly.
Click to expand...
I say the engineer is correct, but you'll need a bond to the neutral at the generator as well.
 
If the neutral is bonded at the generator, then it's a separately derived source, and you need 4 pole switches.

If the neutral and ground come back and only get bonded at the service entrance, then you need 3 pole switches, as the generator would then be a non-separately derived source.

In both cases, the GFI protected main service breaker will work. It's only going to trip when the generator is not running anyway.
 
Pharon said:
If the neutral is bonded at the generator, then it's a separately derived source, and you need 4 pole switches.

If the neutral and ground come back and only get bonded at the service entrance, then you need 3 pole switches, as the generator would then be a non-separately derived source.

In both cases, the GFI protected main service breaker will work. It's only going to trip when the generator is not running anyway.
Click to expand...

Back to my point. This is exactly what must be addressed.
 
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