Grounding a Generator

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mtaylor

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On a generator installation there is no grounding conductor running from the generator to the transfer switch. It will be ground with a grounding electrode to the frame of the generator. Would you use table 250.122 or table 250.66 for this application? I would think that table 250.66 is the correct one. Also, 250.66(A) states that a grounding conductor that is sole connection to the grounding electrode shall not be required to be larger than 6 AWG cu or 4 AWG al. If the only purpose of this conductor is to connect the generator to a 5/8 x 8 CU ground rod would a #6 AWG cu conductor be sufficient? I am looking at the 2008 NEC Handbook - FYI.

Thanks!
 
mtaylor said:
On a generator installation there is no grounding conductor running from the generator to the transfer switch. It will be ground with a grounding electrode to the frame of the generator.
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You must run a grounding means from the generator to the transfer switch.

It is possible if you are not yet under the 2008 NEC that you could use the neutral as the grounding means per 250.32(B)(2) but I doubt you meet all the rules for that.
 
The wiring diagrams I have on this equipment and the installation manual does not show a grounding conductor ran with the service conductors?
 
mtaylor said:
The wiring diagrams I have on this equipment and the installation manual does not show a grounding conductor ran with the service conductors?
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Service conductors do not have anything to do with the feeder from a generator.

And service conductors would not have an EGC they use the neutral as the grounding means.

But the feeder from the generator to the transfer switch needs to include a grounding means and it is very doubtful the the NEC will allow using the neutral of this feeder for the grounding means.

Can I ask why an apprentice is doing this work?
 
mtaylor said:
The wiring diagrams I have on this equipment and the installation manual does not show a grounding conductor ran with the service conductors?
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Then your specs and installation manual do not meet code requirements. There has to be a way to clear a fault, and without a EGC there is no way to provide for a fault path, unless you use an approved raceway.
 
Sorry, I meant the feeder not the service conductors.

I am not the one doing the work.

I spoke with the company that sold the generator and they also said no ground conductor is needed. I am going to see if I can get answers from the manufacturer.

Thanks for the help.

EDIT: There is a circuit breaker inside the generator itself. This with the ground rod to the unit would not protect the system?
 
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I agree with Derek and Bob as well. I would also recomend getting Mike's grounding and bonding book or Soares book on grounding. Both publications would help you with an understanding of grounding and bonding.

Chris
 
mtaylor said:
On a generator installation there is no grounding conductor running from the generator to the transfer switch.
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When you say "grounding conductor", do you mean EGC or grounded conductor? This makes a big difference.
 
All genset manufactures specify a ground rod no matter what. It is a CYA lawyer clause, even though it may serve no purpose. The real question is your genset SDS or not? (Neutral switched or not?) :confused: That determines everything that is required! :cool:
 
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I wouldn't say it serves no purpose, just that it won't clear a fault. If I have a generator on a plastic pad and it get's struck by lightning, I would expect that the ground rod would help to keep some of the current out of the premesis wiring.

Mark
 
Grounding a Generator

dereckbc said:
All genset manufactures specify a ground rod no matter what. It is a CYA lawyer clause, even though it may serve no purpose. The real question is your genset SDS or not? (Neutral switched or not?) :confused: That determines everything that is required! :cool:
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That determines if the generator needs a GES or not, but it does not eliminate the need for a EGC.
 
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