Generator Grounding

D

dvcraven052256

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Location
St. Louis, missouri
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Electrical Engineer
My understanding is I make my transfer switch a 3-pole the generator is grounded through a solid connection to the grounded conductor of the service supplied system. I have attached a PDF of the one line for reference.

Currently I am showing a N-G connection at the generator assuming this is considered a SDS. I believe after some research on SDS and transfer equipment that this is incorrect. I am thinking providing a 3-pole transfer to the generator will make my grounding easier. Your thoughts are appreciated.

Dan Craven
 

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I'm unable to make out the diagram but you are correct if the neutral is switched, the generator is tarted as a SDS.
I rarely see a switched neutral unless the gear has GFP protection.
 
As hillbilly1 mentioned, if there is GFP at the generator (although in this case not code required due to the size of the output feeders), you would put a 4 pole ATS and provide for a N-G bond at the generator.

If you stick to 3 pole ATSs, then remove the N-G bond making it a non-separately derived source at the gen and consider removing the GFP at the generator to avoid false activation due to neutral currents trying to find their way back to their source.
 
dvcraven052256 said:
If I have GFPE at the main panel I will need a 4 pole ATS.
Click to expand...
Not exactly, GFPE at the generator typically leads to a decision. If you use a 3 Pole ATS and remove the N-G bond at the generator, then all GF current will run through the utility part of the oneline. Neutral current wants to return to its source through all paths, but when on generator there is no path for neutral current through the utility N-G bond, since there is no N-G bond at the generator.
You might need to draw a 5 line diagram for it to make sense.
Several articles on the internet have good descriptions.

Choosing between 3-pole and 4-pole transfer switches | Consulting - Specifying Engineer

The choice between a 3-pole and 4-pole transfer switch depends on whether the emergency power system will be a separately-derived source.
www.csemag.com www.csemag.com
 
At 3:10 he says just unbond nuetral so it’s not a SDS but then says you have to be carful because at 3:15 he then shows it hocked back as a SDS and then shows current running through the grounding system also… why did he talk about unbonding so it’s no longer a SDS and the go right back to a SDS model, that model also did not have a switched nuetral- something seemed wrong—


- I get why you have both- and why you need to switch neutral seems like he counter dictated himself or I am just misunderstanding what he stated
 
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