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Thread: 250.122(F)

  1. #21
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    Quote Originally Posted by GoldDigger View Post


    An EGC run separately from the line may, for example, decrease the current from a bolted fault from 25kA to 10kA, but is not likely to affect the trip time of OCPD.

    You probably enjoy sky-diving and swimming with sharks... Just guessing here. Point is, why take the chance?

  2. #22
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    Quote Originally Posted by Dale001289 View Post
    You probably enjoy sky-diving and swimming with sharks... Just guessing here. Point is, why take the chance?
    The real point is, why add a code restriction with no real world evidence there is a safety issue?

    So far all you have done is presumed there is a safety issue based on an exsiting rule for a similar installation.

  3. #23
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    I considered closing this thread since you have ignored the rules (you read them but didn't pay attention to them) for this particular forum. However, since at least four other moderators have commented, I'll let it slide this time. In the future, if you ignore them again, I'll delete the thread as spam.
    "Bob"
    Robert B. Alexander, P.E.
    Answers based on 2014 NEC unless otherwise noted.

  4. #24
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    Quote Originally Posted by rbalex View Post
    I considered closing this thread since you have ignored the rules (you read them but didn't pay attention to them) for this particular forum. However, since at least four other moderators have commented, I'll let it slide this time. In the future, if you ignore them again, I'll delete the thread as spam.
    Speaking for myself, I did not notice that the thread was in the Proposals forum. I bet some of the others made the same mistake.
    Once in a while you get shown the light
    In the strangest of places if you look at it right. Robert Hunter

  5. #25
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    Quote Originally Posted by ActionDave View Post
    Speaking for myself, I did not notice that the thread was in the Proposals forum. I bet some of the others made the same mistake.
    Ditto.
    "Electricity is really just organized lightning." George Carlin


    Derek

  6. #26
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    Quote Originally Posted by jumper View Post
    Ditto.
    Guilty too

    Roger
    Moderator

  7. #27
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    Quote Originally Posted by rbalex View Post
    . . . the rules . . .
    Thanks for the link to the Rules. That was a good read. I hadn't realized the "special handling" engendered by this Forum section.

    Good to know.
    Another Al in Minnesota

  8. #28
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    Quote Originally Posted by GoldDigger View Post


    An EGC run separately from the line may, for example, decrease the current from a bolted fault from 25kA to 10kA, but is not likely to affect the trip time of OCPD.
    I just looked a trip curve for a 100 amp breaker. A 25,000 amp fault is clearly in the instantaneous trip part of the band, but the trip time for a 10,000 amp fault could be anywhere from instantaneous to 2 seconds.

    Edit....those numbers are off by a factor of 10. The currents should be 1000 and 2500 amps, so there would be no difference with that breaker between a fault current of 10,000 and 25,000 amps.
    Last edited by don_resqcapt19; 07-18-16 at 09:56 AM.
    Don, Illinois
    The code only applies to T&M work....it does not apply to contract work.

  9. #29
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    Quote Originally Posted by don_resqcapt19 View Post
    I just looked a trip curve for a 100 amp breaker. A 25,000 amp fault is clearly in the instantaneous trip part of the band, but the trip time for a 10,000 amp fault could be anywhere from instantaneous to 2 seconds.

    don, nice research. I'll bet those 2 seconds will increase as the distance increases, i.e. EGC relative to circuit conductors.

  10. #30
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    Quote Originally Posted by ActionDave View Post
    Speaking for myself, I did not notice that the thread was in the Proposals forum. I bet some of the others made the same mistake.
    I will make that mistake every time....I never look at what forum a thread is in....I just look at new posts.
    Don, Illinois
    The code only applies to T&M work....it does not apply to contract work.

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