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Thread: Grounding electrode conductor size

  1. #1

    Grounding electrode conductor size

    I have been asked to check a ground electrode conductor size. From the utility, there are parallel 3/0 conductors to the MCC. (Two 3/0 per phase, Two parallel conduits, each with the 3 phases and a #4 ground)
    The two #4 grounds from the utility terminate on the MCC ground buss. So far so good. Now, the grounding electrode conductor from the MCC to the ground electrode (the customers ground electrode) is one #2 conductor. From table 250.66 it appears that the grounding electrode conductor should be two #4's. Am I right?

    Thanks for any help

  2. #2
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    You must look at Note 1

  3. #3
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    You do not parallel the grounding electrode conductor. Note 1 states to add the cir. mil of the 3/0 conductors. Table 8 Chapter 9 shows the cir mil for 3/0 at 167,800. Multiple by 2 for the parallel run and you get 335,600-- closest size to that is 350 kcm. Thus you need a 1/0 copper grounding electrode conductor

  4. #4
    Just read it again. ..if I understand it right, it means the ground electrode conductor is sized for the sum of the two 3/0 service conductors...but I'm not sure.

  5. #5
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    Quote Originally Posted by ktm400sx View Post
    Just read it again. ..if I understand it right, it means the ground electrode conductor is sized for the sum of the two 3/0 service conductors...but I'm not sure.
    Correct-- read my post above

  6. #6
    Quote Originally Posted by Dennis Alwon View Post
    Correct-- read my post above
    Ah, just saw that...thank you Dennis

  7. #7
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    Quote Originally Posted by ktm400sx View Post
    Ah, just saw that...thank you Dennis
    You're welcome....

  8. #8
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    What type of customer electrode is it? A CEE would only require a #4 GEC.
    Rob

    Chief Moderator

    All responses based on the 2011 NEC unless otherwise noted

  9. #9
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    Quote Originally Posted by infinity View Post
    What type of customer electrode is it? A CEE would only require a #4 GEC.
    Good point..Since the op mentioned #2 then perhaps it is connected to a ground ring.

  10. #10
    It is a driven steel electrode, I don't know how long..

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