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Thread: ground sizes

  1. #1

    Default ground sizes

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    Lookin for info on what size grounds most people use for personel protection. My illinois company mandates 4/0 as the only acceptable size. Thats comforting on a 138 or 69kv line but it is alittle big for most distribution especiaslly #6cu. They want us to ground to a #2cu or 1/0 al neutral or go to a supplimental. I trying to get the powers tobe to allow 2/0 grounds for distribution depending on wire size. my theory is if a ground is easier to use, it will be used more. thanks

  2. #2
    Join Date
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    N.E. Mass.
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    All we had was 4/0 grounds. They took all the smaller ones off the trucks years ago.
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  3. Default

    We use 2/0 copper grounds on 12 kv and under anything larger gets 4/0

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    Our grounds are sized for the amount of available fault current. Up to 25ka we use 2/0, up to 45ka we use 4/0 and up to 75ka we double up 4/0.

  5. #5

    Cool 2/0 here

    Length is important too. Saw a video of long grounds becoming energized and the whip of the ground broke the ground bars in a substation.

  6. #6
    Join Date
    Feb 2007
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    Ontario Canada
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    All of our grounds are 2/0, but we only work upto 44kv

  7. #7

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    Everybody out there seems to be using larger grounds than we do. We only use #2 copper grounds on distribution. I would be willing to bet they are too small for some of our fault currents, but our engineers probably couldn't figure out the proper sizes.

  8. #8

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    Does not matter what the voltage is. The only question is how much fault current is available and how fast will the breaker operate. Grounds have to be sized to handle the fault current for however long it takes to clear the fault. May very well need to have 4/0 on distribution.

    Pa Ben is also correct, shorter is better. Long ground will whip possibly injuring you. Also longer grounds means more impedance which means the grounds will get hotter and more likely to fail.
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  9. #9

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    #2 here

    our largest sub is a 50mva 14.4x25.6 grounded wye they say thats more than enough they just went through makin sure that was large enough.

  10. #10
    Join Date
    Feb 2007
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    I agree the fault current is the main criteria & for substations 4/0 may be required but for general utility purposes we use 2/0.
    length is also important it is a matter of balance too short & you mite have to join them, too long & you could get into the wipping problem.
    If you use equipotential grounding you could keep them far enough away to minimize the wipping problem

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