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Wiring question

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  • Wiring question

    hello all,

    I have a property in northern wisconsin with a mobile home on it and a detached garage. Just outside the mobile home there is the 200amp utility meter and a distribution panel next to it which then feeds the mobile home on a 100amp breaker and the larger detached garage on a 60amp breaker. This spring Im going to be adding another smaller detached structure about 85' from the distribution panel. Im planning on putting a 40amp breaker in the distribution panel and running #8copper wire in pvc conduit to the new smaller detached building and then installing a breaker panel in that smaller detached building.

    Now to my question, my mobile home and existing detached garage are on 3wire system. Hot, Hot, Neutral wire. There is no seperate ground wire ran back to the distribution panel. Ive been told by a Wisconsin state licienced electrician in the area that I do not need the 4th wire because Im grandfathered in on my two existing buildings. The only reason I would want to add the forth wire he says is if there were other metal pathways between the buildings which there are not.

    The new building on the other hand will have other metal pathways including some cat6 communications wire and some coax for a camera. So, I figure going by his recommendation I would need a seperate ground wire for the new panel in the smaller detached building being built this spring.

    So, would it be acceptable to run the new building as a 4 wire system back to the distribution panel and a 3 wire system from the other two buildings? On the other hand, with copper prices cheaper right now Ive been thinking of just getting a 500' spool of #8 and upgrading all the buildings to 4 wire system. Would a #8 ground wire be acceptable for a 100amp breaker to the mobile home and a 60amp breaker to the larger existing structure? Both of the existing buildings have #2 aluminium wire ran to them. As long as I dont mix the copper and the aluminium on the same lug I should be ok correct?

    Any advice appreciated!


  • #2
    Re: Wiring question

    Well I have worked up north quite a bit and found the inspections to be quite lax to say the least. That said, you are not grandfathered into anything because of your existing service. Any new installation has to be done to current code, which here in Wisconsin is still 2005 NEC. You would need a four wire installation to be done to code. now whether inspectors up there enforce that is the question. I would do it to code in any case.

    You would need a #6 ground for the 100 amp service. Also your #2 aluminum isn't up to code either for a 100 amp feeder to the mobile home. #2 aluminum is good for a residential 100 amp service only. Since you have a 100 amp disconnect before that mobile home, the #2 is no longer large enough to feed 100 amps. You have to follow article 310.16 for sizing the 100 amp feeder.

    And yes you can use both aluminum and copper conductors as long as they are not on one lug. Or if you have to, they make special aluminum to copper split bolts and such.

    So where up north are you?



    • #3
      Re: Wiring question

      This is in the town of Athelstane in Marinette county. I dont even need to have inspections since the work is for outbuildings. Only the primary house needs to have inspections. This is quoted from the people who work at the town hall.

      I do understand what your saying about not being grandfathered in on the new installation. My question is though is it ok to have the two older buildings remain on the 3 wire system and use 4 wires for the new buiding all tied back to the distribution panel? As long as there are no other metal pathways to the two older buildings upgrading to 4 wires shouldn't be neccessary correct?


      • #4
        Re: Wiring question

        Correct. The feeders to the new building will have nothing to do with the feeders to the current buildings.

        I used to hunt Crivitz so I know Athelstane well.



        • #5
          Re: Wiring question

          One more question for ya. The larger outbuilding is on a 60amp breaker in the distribution panel. It has 3 #2 aluminum rhw-2 conductors ran to it in 1.5" pvc conduit the lenght is 140ft. Could I use the #8 copper as the ground wire if I wanted to upgrade that building to a 4 wire system since it's only on a 60amp breaker? The reason I ask is because other metal pathways may be added in the future. And, if I buy a 500' spool of #8 it would be cheaper then getting it cut to exact lenght. I need 4 wires 90' long for the smaller building and then there would be exactly 140' left for the seperate ground wire to the existing larger building.

          Last edited by Palomino; 01-27-2009, 11:03 PM.