Generator Question

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jes25

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Midwest
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Electrician
Lets say we have a small 120V residential transfer panel (unswitched neutral). Now we plug that in to a portable generator receptacle that has the N/G bond.

We know this is a violation because the generator is a SDS. In the example current would flow on the green and white wires in the cord but so what? Please help me understand why this set up is a dangerous.

Note-- I would guess that every 120V transfer panel sold and installed is connected in this manner. :eek:
 
Re: Generator Question

My understanding is that the generator is not a SDS unless you switch the neutral. In your example the neutral in the transfer switch is not switched, thus the generator is not a SDS.

However, I do believe the N-G bond in the generator should be lifted. The N-G bond in the generator acts as a main binding jumper when the generator is a SDS (i.e. when connected to a 4 pole xfer switch).
In the example current would flow on the green and white wires in the cord but so what?
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The problem is that you end up with some of the "normal" current that is supposed to be flowing in the neutral flowing in the green (EGC) instead. That can energize metal parts. Current is only allowed to flow in the EGC when there is a fault and that should only be long enough to trip the OCPD.

See mike holts pics and explanations of "objectionable current" I don't have a book in front of me but the NEC prohibits this objectionable current somewhere in the grounding section.
 
Re: Generator Question

Since the neutral is unswitched, it's not a SDS.

That demotes the generator to almost "appliance" status. It's equipment installed after the service.

Why can't you connect the neutral to EGC's after the service? Because neutral current will flow on the EGC's.

It's a violation of 250.6(A).

Joe, do a search on bonding and SDS, and you will see some good discussions on the topic. :)
 
Re: Generator Question

jes,
because you can not have a portable generator that has 120V recptacles on it that does not have a N/G bond.
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That's what I thought too, but then I did some research and found that many portable generators with 120 volt receptacles do not have a neutral to case bond.
Don
 
Re: Generator Question

I would not want to use it for, say a metallic drill that faults. :eek:

[ November 14, 2005, 07:59 PM: Message edited by: jes25 ]
 
Re: Generator Question

If you were holding the drill and touching aluminum siding and the generator frame was touching the siding.

[ November 14, 2005, 08:18 PM: Message edited by: jes25 ]
 
Re: Generator Question

Originally posted by jes25:
If you were drilling into aluminum siding and the generator frame was touching the siding.
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Not really a circuit there as the generator frame under discussion is not bonded to the generators output. :)
 
Re: Generator Question

Most of these units have GFCI protection so if you did find a way to make a circuit at least you would have some protection.
 
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