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I Will be installing a subpanel in a detached garage. The subpanel will be 60 amp. The garage is about 30' from the main-panel in-house, and I will of course get an exact length before selecting the proper gauge wiring. I'll be using pvc underground for the wiring. There is already existing wiring going underground from the house to the garage, which will no longer be used. When it comes to grounding this subpanel, should I run a grounding conductor from the main panel to the new sub, or ground the sub to earth?

Reading this answer sounds like I would have to ground the subpanel to the main, primarily because in my situation this is a new install. All other variables I have control over.

  • If so, I would be running 4 wires from the main panel to the sub, 2 hots, 1 neutral, and 1 ground correct?

  • Then, at the subpanel, the ground bus bar and the neutral bus bar would not be connected, and the grounding screw removed from the ground bus bar?

  • Lastly, a GFCI Breaker must be used at the main, right? I believe this is true for any subpanel in a detached building, just want to be sure.

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The NEC allows for both approaches, independent grounding electrodes or grounding along with feeder conductors. With independent grounding, the neutral is bonded to the grounding system, when grounding with feeder it is not. The grounding bus is always bonded to the enclosure no matter what. I've no idea about GFCI requirements, that requirement was introduced after I stopped following updates to the code. –  bcworkz Apr 23 at 1:29
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@bcworkz New work requires a grounding conductor be run with the supply (see 250.32(B)(1)). –  Tester101 Apr 23 at 15:04

1 Answer 1

up vote 1 down vote accepted
  • Pull 4 conductors (2 ungrounded (hot), 1 grounded (neutral), 1 grounding) (250.32(B)(1)).
  • Grounded (neutral) and grounding bus must be separate at sub-panel (250.32(B)(1)).
  • No need for a GFCI breaker in the main panel, unless your local code requires it.
  • A grounding electrode is required at the second structure (250.32(A)).

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Grounding Electrode == #6 gauge wire attached to copper rod driven 8ft into ground? –  BigHomie Apr 23 at 15:48
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2 ground rods minumum 6' apart unless you already got another type of electrode out there. –  Rand Apr 23 at 15:58

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