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I have an outbuilding with a subpanel. I realized that the subpanel was wired to use the same bus bar for ground and neutral, which I understand is not the correct way to do things, and I'd like to fix it if that's possible.

In the diagrams I've seen, the subpanel's ground bus will connect to a grounding electrode and also to a ground wire leading back to the main panel. Unfortunately the cable to the outbuilding does not have a ground wire, nor metal conduit, and I am unable to run new cable between the panels.

My options are to leave things as-is, with bonded neutral and ground in the subpanel, or to separate the neutral and ground at the subpanel and rely on the grounding electrode for the outbuilding's ground. I know neither of these options are ideal, but is one of these preferable over the other?

Thanks

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    Even though you're not able to run a new cable, is running a new separate wire also out of the question?
    – brhans
    Sep 11, 2023 at 14:06
  • How many amps is this feeder rated for, and is it fed directly from the main panel or from an upstream subpanel at the house? There may be another way to fix this problem but it requires a slightly unusual part Sep 12, 2023 at 2:35
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    It's fed directly to the main by wires buried underground with no conduit and no ground wire. There is a double 60 amp breaker at the main for this panel. Sep 12, 2023 at 15:28

1 Answer 1

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The key question is: When was this subpanel originally installed?

According to this previous question, separate ground became a requirement with NEC 2008. Assuming your subpanel is older than 2008, or whenever your jurisdiction adopted NEC 2008, it is grandfathered.

Do not separate neutral and ground without having a ground wire back to the main panel. That would leave your ground floating relative to neutral, which is not a good thing. It is possible for there to be a significant different between ground rods at the main building and an outbuilding, and without a ground connection between the two buildings, wacky - and dangerous - things can happen.

While inside a building it is generally easy to retrofit a ground, it is a bit harder to do so to a separate building. Without conduit, any ground wire would have to be either trenched appropriately or go up - you can't leave it on the ground. And if you trench it, you can't just throw a single wire in there, you have to use an appropriate burial rated cable. So no easy fix.

However, if your subpanel was installed after your local jurisdiction adopted NEC 2008 then you really need to fix it. Which would probably mean running conduit plus wires or a new buried cable.

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  • Thank you. Installed 1989. Sep 11, 2023 at 15:17
  • Then you're grandfathered. (Well, your panel is, I know nothing about your family :-) ) Sep 11, 2023 at 15:17
  • @scottdegen -- see my comment on the question -- this may be fixable without running additional wires, but we'll need to know more about your setup Sep 12, 2023 at 2:36

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