Generator Question/opinion

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willdogyou

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I have a question about the hook up of a generator. It is going to be used when the utility goes down. It's going on a 480v 3 phase 3 wire system. The service lateral has no neutral. We are matching that from the gen-set to the transfer switch. It is a mid size system, 6 parrallel runs 500mcm, 250mcm equipment grounds. We are attaching the grounds to the gr. bar and then to the frame. There is no neutral at the service equip. the generator has a fault sensor attached on the neutral bus inside the gen.
On to the question, Should the neutral bar in the gen-set be bonded to the ground bar? All my training tells me that it should but, Engineers over the project say "No".
I'm sure that similar questions have come up before. In my area (Pensacola, FL) Grounding is THE MOST disagreed upon section of the Code between inspectors and engineers. Thanks for your input.
 
I hope I read your post correctly sometimes I do not read them verbatim. separately derived systems must be grounded at the the "Bullseye" point I think it is 05' NEC 250.30
 
Are you installing a grounding eletrode system at generator? If so I would say that based on your question you have a seperately derived system because there is no neutral conductor being supplied via the utility so the xo of the generator could be and should be bonded to the new grounding eletrode system and the equipment grounds of the utility service.
 
Yes, There is a grounding grid at the Gen-set. There is also a Main ck. Breaker on the Gen-set. I would see it as a seperately derived system also.
I apolojize for not being clear on exactly what I'm asking, I know it is hard to visualize without actually seeing it.
 
dcspector said:
I hope I read your post correctly sometimes I do not read them verbatim. separately derived systems must be grounded at the the "Bullseye" point I think it is 05' NEC 250.30
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So who said a generator is an SDS? The designer makes that choice, not the code.

This system is no different just becuase the service is 3-wire. It all depends on what type of protection devices the engineer is using to protect the generator and the conductors.
 
dereckbc said:
So who said a generator is an SDS? The designer makes that choice, not the code.

This system is no different just becuase the service is 3-wire. It all depends on what type of protection devices the engineer is using to protect the generator and the conductors.
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I am basically asking for an opinion if everything is kosher. I was told that the fault sensor on the neutral is to be hooked to the ck. breaker at the generator and the neutral bar is NOT to be bonded to the ground bar.
My better judgement tells me to run full size nuetral conductors to the service equipment from the gen-set as well as the equipment grounds if you do not bond the two.
 
My answer depends on one thing, Do you use a neutral in your system that is bonded to your EGC (any where up to and including at the primary side of a transformer). If yes, then run a 5 wire and connect the neutral from the generator to the system neutral at the transfer switch (regardless of what the poco is supplying). If, instead you do not use a neutral anywhere before traversing a transformer, then I would instead say contact the equipment manufacturer for their recommendation, but more than likely you would connect the neutral to the EGC at the generator or at the transfer switch. The only reason I say to contact the manufacturer is to see if there could be any negative reaction resulting from not connecting the neutral at all (if it's not even used).

After all that, if you have another connection from the facility back to the generator (ie control circuit), IMO you would then need to run a neutral back to the service rated transfer switch and bond to the EGC at that point.
 
dereckbc said:
So who said a generator is an SDS? The designer makes that choice, not the code.

This system is no different just becuase the service is 3-wire. It all depends on what type of protection devices the engineer is using to protect the generator and the conductors.
Click to expand...

Derek if there is no neutral connections solidly interconnected to the service the transfer switch opens the neutral. The grounding bullseye would be at the generator then that would be a SDS....which I thought the OP was asking as far as grounding at generator.....or am I confused?

Thanks Derek

Greg
 
I have a couple of questions.

Is the system supplying the building an UNGROUNDED system?
Isn't GFP of systems for Wye connected systems? The generator may not be the correct generator???

Derek
I am not sure I understand your post.
My understanding if a generator is to become a separately derived system is due to the configuration of the transfer switch. Is this not correct?
 
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Pierre C Belarge said:
I have a couple of questions.

Is the system supplying the building an UNGROUNDED system?
Isn't GFP of systems for Wye connected systems? The generator may not be the correct generator???

It's actually a waste water treatment facility. Gen-set feeds MCC that has its own service. No neutral from Gen-set or Service. For lighting and power they hit a step down trans. which derives its neutral.
Basically you have 3 hots, 1 ground from Gen-set. Gen-set derives a neutral that is not being used but do you bond it to ground?
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