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Thread: Alt Grounding Method

  1. #1
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    Alt Grounding Method

    This isn't a grounding vs bonding question, but it seems that various ground related questions are in this forums, I apologize if I'm in the wrong place. I have 4000 amp service disconnect outside feeding a 4000 amp MDP inside. I believe it is 11 runs of (4) 500 MCM's with a 1/0 ground. I have always been taught to put the ground inside each set per pipe, I actually only recently learned about isolated phase's with underground parallel pvc installations. My question is, Is there another code compliant method to run the ground, lets say per 250.122 with one 500 mcm copper ground from Main disconnect to MDP. I just had to order a bunch of 1/0 lugs because the main disconnect and inside MDP only came with one large lug on each ground bar, and I was wondering if there was another way in the future to do an install with one larger ground and that lug instead of ordering for and pulling 11 1/0's?

  2. #2
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    Not sure where you are getting 1/0 from. You actually have to pull a 500KCMIL ground in every conduit. 250.122 (F)


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  3. #3
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    Since this is a feeder I agree with Strathead your EGC in each parallel raceway should be based on the 4000 OCPD and T250.122.
    Rob

    Moderator

    All responses based on the 2014 NEC unless otherwise noted

  4. #4
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    The engineer specc'd it, see attachment. Thank you for your response, I always know the Holt forum guys will shoot me straight. I'll get an RFI together and make sure it gets put in right. I feel like I've never pulled a 500 MCM ground into a 4000 amp service, but I guess now that I think about it the recent ones didn't have the disconnect and went straight from XFMR to a MCB MDP which would scratch the ground.
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    Last edited by infinity; 12-19-17 at 05:22 PM. Reason: My mistake
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  5. #5
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    Quote Originally Posted by Strathead View Post
    Not sure where you are getting 1/0 from. You actually have to pull a 500KCMIL ground in every conduit. 250.122 (F)
    Yep, and the OP is not going to be happy. 500 CU it is.

  6. #6
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    Quote Originally Posted by kyleapec View Post
    The engineer specc'd it, see attachment. Thank you for your response, I always know the Holt forum guys will shoot me straight. I'll get an RFI together and make sure it gets put in right. I feel like I've never pulled a 500 MCM ground into a 4000 amp service, but I guess now that I think about it the recent ones didn't have the disconnect and went straight from XFMR to a MCB MDP which would scratch the ground.

    This is a pretty common mistake on parallel feeders. I'm guessing that they got the #1/0 from the incorrect table 250.102(C).
    Rob

    Moderator

    All responses based on the 2014 NEC unless otherwise noted

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