Residence Generator Panel Add-on

[ramdiesel3500]

I have been asked to install a transfer switch and generator panel in a residence. The proposed design involves extending the ungrounded conductors of the new "emergency power" branch circuits through a nipple into the new generator panel. Now two things bother me here. First, by extending the circuits, there will be generator power running through the service panel via the extended ungrounded branch circuit conductors. Second, the grounded conductors will not be extended to the new panel.
It just seems to me that there must be a code violation here, but I have not been able to find one.
Any input or views on this will be greatly appreciated!
Thank-you in advance!

 

[charlie b]

Re: Residence Generator Panel Add-on

I'm not sure I understand. Let me try to describe your situation.
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• <font size="2" face="Verdana, Helvetica, sans-serif">You add a generator and a transfer switch and generator panel.</font>
• <font size="2" face="Verdana, Helvetica, sans-serif">The connection from the utility to the service panel will remain untouched.</font>
• <font size="2" face="Verdana, Helvetica, sans-serif">There will be a new connection from the utility to the transfer switch. The generator will also connect to the transfer switch. The output of the transfer switch will go to the generator panel.</font>
• <font size="2" face="Verdana, Helvetica, sans-serif">Loads that are not to be on the generator will remain connected to the service panel.</font>
• <font size="2" face="Verdana, Helvetica, sans-serif">Loads that will be on the generator will be disconnected from the branch circuit breaker in the service panel, and connected instead to a branch circuit breaker in the generator panel.</font>
• <font size="2" face="Verdana, Helvetica, sans-serif">Instead of running new conductors from the generator panel to these loads, a set of shorter conductors will be run from the generator panel to the service panel, and spliced to the conductors that go from the service panel to the loads.</font>
• <font size="2" face="Verdana, Helvetica, sans-serif">There will be no neutral wires running between the service panel and the generator panel. However, the neutral buses of these two panels will be connected, as part of the wiring process for the transfer switch.</font>

<font size="2" face="Verdana, Helvetica, sans-serif">First, do I have that description right?

If so, I think you have a violation of 300.3(B). The ungrounded and grounded conductors must be in the same raceway. Running ungrounded conductors from the service panel to the generator panel, without also running grounded conductors in the same raceway, is not allowed.

But as to having generator power run through the service panel, as though the service panel were no more than a junction box, I don't think that is a violation.

 

[ramdiesel3500]

Re: Residence Generator Panel Add-on

Charlie b
Thank-you for the response. I forgot to say that the transfer switch will be fed from the service panel with a new 2-pole 100A breaker. Otherwise, your description is perfect! Now I need to figure out how the makers of these little generator panels with the individually switched circuits get around the 300.3(B) requirement.

 

[ccjersey]

Re: Residence Generator Panel Add-on

can all the conductors to and from the generator panel go through the same nipple to prevent inductive heating without derating?

 

[wyatt]

Re: Residence Generator Panel Add-on

This set up seems to be the norm in the home use standby gen I put in, they even come pre wired with a 2' flex with 12 branch circuit condutors with 1 gounded condutor sized to carry the load of the emer. panel, ready to splice in the old panel. We have had it questioned by a inspector before. But some has had to approve the set up for the manufactor.