Please let me know if this sounds correct-

Sub panel fed from 80amp breaker in main building 200amp load center. Roughly 75' of 1" PVC conduit from existing load panel, under existing timber deck, underground for ~6', stub up outside building, wall penetration to interior main lug load center with 6 branch circuits (1 240V outlet, 4 120V outlets/lighting)

1" PVC Sch 40 Conduit fill- 3x #4 THHN (Hot, Hot, Neutral) 1x #8 THHN (Ground, bonded to main structure load panel ground and ground rod at outbuilding)

Neutral and ground to be isolated in all new wiring.

Thanks for any comments!

  • What is the total distance (along the wire) from the breaker in the main panel, to the breaker in the second panel?
    – Tester101
    Jan 15, 2015 at 22:45
  • I strongly suggest you don't consult this site for a question like this. Find a qualified electrician (verifiable) to verify your calculations. Jan 15, 2015 at 23:08
  • BTW - underground pipe is considered a wet location. Make sure that wire is dual rated THHN/THWN or plain THWN. Jan 16, 2015 at 1:05
  • 1
    Pull a permit from whatever jurisdiction has authority and then ask them these questions. They will tell you what is required in your area. Jan 16, 2015 at 5:29
  • @ChiefTwoPencils I don't think DIYers can buy (or maybe they don't manufacture) THHN, everything I've ever seen at home centers is THHN/THWN.
    – Tester101
    Jan 18, 2015 at 0:25

1 Answer 1


I'm not entirely sure what you mean by "neutral and ground to be isolated" but it's my understanding that they should always be connected so that there is zero potential between them.

My understanding is also that only connection between neutral and ground should be at the main panel. If you connect the neutral to the ground in a second location (the garage) then you'll create a "ground loop".

I'm not an electrician and it's been about 10 years since I read the electrical code so I could be mis-remembering.

  • 1
    The grounded (neutral) conductor, and the grounding conductor should only be bonded at the service equipment. Therefore, they should be isolated from one another in the second panel.
    – Tester101
    Jan 15, 2015 at 22:43
  • That's what I said. But your use of the word "isolated" makes me realize what he meant in his original question. So we're all saying pretty much the same thing. Jan 17, 2015 at 22:31

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