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sub panel wiring grounding question

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  • #16
    Re: sub panel wiring grounding question

    Originally posted by swampfox View Post
    so, now youv'e got a 4 wire feeder to a sub panel with the neutral isolated, the grounding conductor tied down to the sub panel box itself and to 1 or 2 ground rods with a #8 bare.

    Youv'e just tied your house main service electrode conductor to 2 seperate grounding systems.
    That's a no no.
    If the main service grounding electrode conductor fails or is a poor ground, the garage may carry a fault current from the main.The new ground system at the garage is not designed or intended to do so.
    Welcome to the forum swampfox, from Newnan Ga.

    I think you need to check the facts.The 08 code requires all detached buildings to be wired this way. It has always been a practice to wire them this way, and I have never had one fail inspection.

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    • #17
      Re: sub panel wiring grounding question

      JBFan,
      Thank you for your post.

      And that's exactly why I quoted the NEC 08 update in my prior post on this issue. Subpanel (feeder) wiring is one of THE most misunderstood of all the issues, and if you ask 10 sparkies or 10 sparky inspectors to talk about this issue, you will most likely get a total of 20 different responses.
      Cheers,
      Jim Don

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      • #18
        Re: sub panel wiring grounding question

        I never said the code didn't say that..
        I simply stated the facts.
        Codes are changed for reasons.
        Is it not true what I stated.


        What if the house main were a 400amp service with the correct electrode conductor grounding it
        You run a 100 amp circuit to a detached garage, 4 wires, and drive a ground rod. Isolate the neutral, tie the grounding conductor to a bar along with an electrode conductor sized for 100 amp wire
        Say the 400 amp ground is bad, you drove 2 rods to keep from having to test it, so you were never sure to begin with. Now the whole system is grounded at the garage with an under sized electrode conductor.

        I know what the code says and I have to do it that way too

        It just doesn't add up thats all

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        • #19
          Re: sub panel wiring grounding question

          The ground in the garage would only operate for a short time till the breaker tripped. If you didn't have the ground in the garage you would have no ground at all. Of course that is the advantage of a good fuse since they trip so much faster than a breaker. I put a 100 amp panel in my buddies garage to run a CNC machine, lathe, etc., and I installed a 100 amp safety switch at the door with FRS fuses. Anything goes wrong the fuses will trip instantly or you can throw the handle in an emergency.

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