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Thread: 250.122(F)

  1. #11
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    Quote Originally Posted by don_resqcapt19 View Post
    But the impedance of that remote fault clearing path will be substantially higher than if the EGC was in the same conduit. Maybe high enough that the fault current will be limited enough that the breaker will operate in its short time trip range and not in the instantaneous trip range.
    As I recall from the IEEE green book, a 3' separation between the ungrounded conductors and the EGC can double the impedance of the fault return path.
    Correct - when the EGC is routed with phase conductors, it creates a low impedance path due to magnetic flux of the surrounding phases - much like a neutral on a balanced system.

  2. #12
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    Just install the tray continuous from point to point and use the tray as the EGC, you're done.

    Roger
    Moderator

  3. #13
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    Quote Originally Posted by roger View Post
    Just install the tray continuous from point to point and use the tray as the EGC, you're done.

    Roger
    Not so fast Roger - we're not discussing what the code says but rather what it should say...at least according to me

  4. #14
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    Quote Originally Posted by Dale001289 View Post
    Not so fast Roger - we're not discussing what the code says but rather what it should say...at least according to me
    Data, test studies with peer review, and published articles from respected sources are your back up or is this just a silly fishing expedition?

    Yeah, I am bit harsh.
    "Electricity is really just organized lightning." George Carlin


    Derek

  5. #15
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    Didn't we have this argument earlier this year?
    Once in a while you get shown the light
    In the strangest of places if you look at it right. Robert Hunter

  6. #16
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    Quote Originally Posted by ActionDave View Post
    Didn't we have this argument earlier this year?
    Yes, AFAICT the consensus was that Mcdonald's makes the best fries and that Carl's Jr. has a better burger.

    I maybe confusing forums though.
    "Electricity is really just organized lightning." George Carlin


    Derek

  7. #17
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    It would seem the EGC is as protective as the grounded conductor as all EGC eventually tie to the grounded conductor -- when installing multi circuits in a raceway we only are required to size the EGC according to the largest OCPD. Adding EGC for each branch circuit would not create a better path.. GEC are a different subject matter when discussing purpose.
    CircuitRyder --- Unfortunately not all good ideas are code enforceable.

  8. #18
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    Quote Originally Posted by jumper View Post
    Yes, AFAICT the consensus was that Mcdonald's makes the best fries and that Carl's Jr. has a better burger.

    I maybe confusing forums though.
    Now wait a minute, are we talking french, wedge or waffle fries?

  9. #19
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    Quote Originally Posted by Dale001289 View Post
    when the EGC is routed with phase conductors, it creates a low impedance path due to magnetic flux of the surrounding phases - much like a neutral on a balanced system.
    You seem very hypnotized by the repetition of this meme. The way you state it implies that a low impedance path IS NOT present in any other configuration . . . which is just plain silly.

    I support Bob's suggestion to actually work from real world situations that fail. Do a forensic analysis of the assembly, model it mathematically and demonstrate your case.
    Another Al in Minnesota

  10. #20
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    Quote Originally Posted by al hildenbrand View Post
    You seem very hypnotized by the repetition of this meme. The way you state it implies that a low impedance path IS NOT present in any other configuration . . . which is just plain silly.

    I support Bob's suggestion to actually work from real world situations that fail. Do a forensic analysis of the assembly, model it mathematically and demonstrate your case.


    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.

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