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Old 12-30-2008, 06:55 PM   #1
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Feeding multiple generator subpanels from a single generator


I have two 200 amp main panels, each feeding an independent generator subpanel (subpanels have mechanical interlocks). I want to feed both subpanels with a single generator that's capable of powering the entire system. Running the hot wires seems pretty straightforward - feed one of the subpanel generator supply breakers directly from the generator, then use a split bolt or multi-wire tap to feed the other. Where I get stumped is how to wire the neutral/ground in a way that meets the NEC. I don't think that I want to branch the neutral/ground from one subpanel to the other because this would ultimately make a loop in both conductors (subpanel A -> main panel A -> CT -> main panel B -> subpanel B -> subpanel A). Yet connecting the neutral/ground at just one subpanel also feels "wrong" even though it should work just fine. My understanding is that you want all conductors carrying the same load to be in physical proximity, so I'm thinking that it make be questionable having the hot conductors separate from the neutral/ground path. If this is true then that means that I'm stuck trying to find a way to switch the neutrals, and I think that this is a pretty expensive proposition. Am I just being overly conservative worrying about feeding the neutral/ground from one subpanel to the other using the existing path through the main panels and CT? Would such an arrangment pass an inspection?

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Old 12-30-2008, 10:53 PM   #2
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Feeding multiple generator subpanels from a single generator


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Originally Posted by toddbu View Post
I have two 200 amp main panels, each feeding an independent generator subpanel (subpanels have mechanical interlocks). I want to feed both subpanels with a single generator that's capable of powering the entire system. Running the hot wires seems pretty straightforward - feed one of the subpanel generator supply breakers directly from the generator, then use a split bolt or multi-wire tap to feed the other. Where I get stumped is how to wire the neutral/ground in a way that meets the NEC. I don't think that I want to branch the neutral/ground from one subpanel to the other because this would ultimately make a loop in both conductors (subpanel A -> main panel A -> CT -> main panel B -> subpanel B -> subpanel A). Yet connecting the neutral/ground at just one subpanel also feels "wrong" even though it should work just fine. My understanding is that you want all conductors carrying the same load to be in physical proximity, so I'm thinking that it make be questionable having the hot conductors separate from the neutral/ground path. If this is true then that means that I'm stuck trying to find a way to switch the neutrals, and I think that this is a pretty expensive proposition. Am I just being overly conservative worrying about feeding the neutral/ground from one subpanel to the other using the existing path through the main panels and CT? Would such an arrangment pass an inspection?
There's two options when wiring generators to panels. Either get a transfer switch that switches the neutral, or disconnect the ground and neutral bond in the generator.

You want only one place for the neutral bond to ground. This would be the main disconnect. After that, everything should be fed with four wires and the neutral isolated. Your generator should feed in with 4 wires. Option 1 takes care of this by switching the neutral from the main, and letting the bond happen at the generator. Option 2 takes care of it at the main. So, in a sense, with option 2, the ground wire at the generator is really coming from the panel, instead of going to the panel.

This is a pretty advanced setup. You might want to get an electrician to do it.

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