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I have a 60 amp subpanel in my garage and plan to add a second 30 amp subpanel to an out-building 130 ft away (fed from the 60 amp). I Plan to run 6 AWG 4-wire from the 60 amp to the 30 amp in 1 1/2 in PVC buried 18 in. My understanding is that I must keep the neutral & ground from the 30 amp separate from the 60 amp (e.g. the ground goes to a separate ground rod [or two] at the out-building and the neutral runs back to the main service entrance). If I understand this correctly, I have a problem in that I do not have a means of getting the neutral from the new 30 amp back to the main service entrance.

  1. Is my understanding regarding the ground & neutral correct?
  2. If so, are there other options (current needs a return to source so I doubt it)?
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The new 30A panel needs a 4-wire feeder from the 60A panel. This is two hots, a neutral and an equipment ground.

The remote 30A panel also needs a grounding electrode (or two) since it is in a detached structure. This grounding electrode has NOTHING to do with the equipment ground run with the feeders. The two serve very different purposes.

In the existing 60A panel you will terminate the new ground to the ground bar and the new neutral to the isolated neutral bar.

  • Thanks Petey. Sorry I wasn't clear regarding grounding electrode and equipment ground; got those covered. The neutral was my primary concern. Got that now too! Thanks. – Thom Oct 26 '14 at 14:19
  • @SpeedyPetey You mentioned the isolated neutral bar in the remote subpanel, but didn't explicitly state that the ground bar and neutral bar in the subpanel must not be bonded. – Craig Nov 24 '14 at 8:56
  • @Craig, then I guess you just did, right? That was what I meant by isolated neutral bar. IMO that is self explanatory. – Speedy Petey Nov 24 '14 at 12:04
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    @SpeedyPetey, I guess I did. :-) I knew that's what you meant. It's just that this is a DIY forum and I try never to make assumptions with folks where the cost of pointing out an important detail is pretty low. And in this case it's obviously important that the ground and neutral bus be isolated from one another in subpanels in order to avoid creating a circuit that energizes the ground downstream from the subpanel, which a casual DIYer might not understand. In which case they probably should call an electrician, but you know they probably won't. That's all I was doing... :-) – Craig Nov 24 '14 at 17:28
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If you are running 4-wire from the 60A to the 30A, and the 60A is connected correctly, you already have "a neutral return to the service entrance" in the form of the neutral wire feeding the 60 A box.

The ground and neutral bars at both sub-panels should be separate (with the Neutral isolated from the box), and the Neutral wire should be connected to the neutral bar, the Ground wire to the ground bar; at both ends.

If your understanding was that the 30A panel needed a wire back to the service entrance separate from the neutral and ground feeding the 60A box, that is an incorrect understanding. The "separation" for sub-panels is in keeping the Neutral (or grounded, white) conductor separate from the Ground (or grounding, green) conductor.

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    The "exception" to use a 3-wire feeder was removed from the code long ago. It is highly unlikely that anyone could still take advantage of that exception. – Speedy Petey Oct 25 '14 at 2:13
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    Showing my age - - edited out. – Ecnerwal Oct 25 '14 at 2:18
  • @Thom already mentioned it in the question. – Ecnerwal Oct 25 '14 at 21:06

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