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Simple question on design of electrical subpanels Wayne Whitney 07-14-2006
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Posted by Wayne Whitney on July 14, 2006, 5:35 pm
Hello,

Is it standard for a residential electrical subpanel to use its
chassis as a ground backplane? I.e. the ground from the incoming
4-wire feed terminates at a lug bolted to the back of the panel, and
the ground bar is also just bolted to the back of the panel.

Thanks, Wayne


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Posted by RBM on July 14, 2006, 7:05 pm
Yes, that's fine. On a sub panel you don't want the neutral buss to be
bonded to the enclosure


> Hello,
>
> Is it standard for a residential electrical subpanel to use its
> chassis as a ground backplane? I.e. the ground from the incoming
> 4-wire feed terminates at a lug bolted to the back of the panel, and
> the ground bar is also just bolted to the back of the panel.
>
> Thanks, Wayne
>



Posted by Wayne Whitney on July 14, 2006, 7:08 pm

> Yes, that's fine. On a sub panel you don't want the neutral buss to
> be bonded to the enclosure.

Thanks, I understand the part about the neutral buss being kept
separate from the ground buss in subpanels. And obviously the
subpanel chassis needs to be tied to the equipment ground. I was just
surprised to the subpanel chassis as part of the fault current path
for all the circuits served by the subpanel. That's fine?

Thanks, Wayne


Posted by RBM on July 14, 2006, 7:41 pm
If you have metallic cables or conduits, their connection to the chassis is
their path to ground


>
>> Yes, that's fine. On a sub panel you don't want the neutral buss to
>> be bonded to the enclosure.
>
> Thanks, I understand the part about the neutral buss being kept
> separate from the ground buss in subpanels. And obviously the
> subpanel chassis needs to be tied to the equipment ground. I was just
> surprised to the subpanel chassis as part of the fault current path
> for all the circuits served by the subpanel. That's fine?
>
> Thanks, Wayne
>



Posted by Wayne Whitney on July 15, 2006, 9:18 pm

> If you have metallic cables or conduits, their connection to the chassis is
> their path to ground

Hmm, good point--it is permissible to use some conduit systems as the
EGC in the branch circuits, so then subpanel chassis is part of the
fault current path for those circuits. However, while this may meet
the NEC, I would not consider this to be the best practice. So
perhaps that is the answer to my original question.

Cheers, Wayne


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