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Thread: how to size equipment ground wire (600V) for MV cable?

  1. #1
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    how to size equipment ground wire (600V) for MV cable?

    Does anyone know any methods / rule how to size equipment ground wire (600V) for medium voltage cable.

    Example:

    Load: 250A at 4.16kV, MV cable use: 2/0, 5kV. What is equipment ground wire (600V) to be used to be run with above MV cable?

    Same question for 2/0, 15kV cable.

    Thanks a lot!

    anbm

  2. #2
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    What size over current device do you have?

    See 250.122

  3. #3
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    350A CB but at 4.16kV not 600V, not sure we can use NEC 250.122 for this application.

  4. #4
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    Quote Originally Posted by anbm
    not sure we can use NEC 250.122 for this application.
    I don't think you have a choice. :smile:

    See Part X of Article 250 and specifically 250.180

  5. #5
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    Quote Originally Posted by iwire
    (cut) See Part X of Article 250 and specifically 250.180
    (NEC 2008)
    250.180 is certainly important, including the part that says to look at 250.182 - 250.190.

    For a single point, solidly grounded system, look at 250.184.B.8. 250.122 doesn't apply. You have to engineer this one. There is no NEC cookbook answer.

    If the system is impedance grounded, look at 250.186.D. Could be 250.122 does apply here.

    The code has changed since 2002 cycle. I don't have a 2002 in front of me, but as I recall, the section on impedance grounded was different - pretty much required engineering. So depending under which code cycle the system was built could also give a different answer.

    cf

  6. #6
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    Quote Originally Posted by Cold Fusion
    (NEC 2008)
    250.180 is certainly important, including the part that says to look at 250.182 - 250.190.

    For a single point, solidly grounded system, look at 250.184.B.8. 250.122 doesn't apply. You have to engineer this one.
    If he is running an EGC which he said he was 250.122 would apply.

  7. #7
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    I think a real question here is should he be running an EGC at all?

  8. #8
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    Quote Originally Posted by iwire
    If he is running an EGC which he said he was 250.122 would apply.
    (NEC 2008)
    I'm lost. 250.184.B.8 says it applies to "equipment grounding conductors" under the conditions I listed. What did I miss?

    cf

    edited to add NEC cycle
    Last edited by Cold Fusion; 10-25-08 at 03:10 PM.

  9. #9
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    Quote Originally Posted by iwire
    I think a real question here is should he be running an EGC at all?
    Oh-oh, lost again. The OP description appears pretty normal for a 13.8kV industrial distribution with xfms to 4160V for selected large motors.

    I can't think of a reason why one sould not want to run an EGC.

    cf

  10. #10
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    I am thinking if we convert breaker size 350Amp at 4.16kV to XYZ Amp at
    600V and apply 250.122 to figure out what Equipment ground wire needed? Well, the ground wire size will ends up huge...anyone agrees on this approach? (-:

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