Data Center Generator

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NEC User

Senior Member
I'm designing a data center (significant amount of IT loads) with a back-up generator and I'm trying to determine if I should use a 3 pole or 4 pole ATS. Should the fact that the generator will back up sensitive electronic equipment affect my decision?
 

Pharon

Senior Member
Location
MA
I always prefer separately derived (4 pole ATS) over non separately derived (3 pole ATS) systems. I can't think of any argument why a non separately derived system would be better. The only time I would implement one is if it's part of an existing system that only has 3 pole ATSs.
 
Should the fact that the generator will back up sensitive electronic equipment affect my decision?

Presuming that the only equipment actually powered by the generator is a UPS, lights, and HVAC, I'm not sure it matters much at all, power-quality-wise. You may prefer wiring the generator as an SDS for other reasons. I generally see them as non-SDS with 3-pole ATS.
 

jrannis

Senior Member
I always prefer separately derived (4 pole ATS) over non separately derived (3 pole ATS) systems. I can't think of any argument why a non separately derived system would be better. The only time I would implement one is if it's part of an existing system that only has 3 pole ATSs.

Interesting opinion.
Why would there be a benefit to opening the neutral?
 

ron

Senior Member
If this is a large 480V load / generator, I typically leave the neutral at the alternator with a neutral to ground bond, then don't need to worry about carrying a neutral down stream. The small amount of 277V loads get a 480 - 480/277V transformer.
 

jtinge

Senior Member
Location
Hampton, VA
Occupation
Sr. Elec. Engr
If this is a large 480V load / generator, I typically leave the neutral at the alternator with a neutral to ground bond, then don't need to worry about carrying a neutral down stream. The small amount of 277V loads get a 480 - 480/277V transformer.

This is the same thing we are doing on a large data center we are currently constructing.
 
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