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Thread: Conductors in Parallel

  1. #1
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    Conductors in Parallel

    Do you feel parallel conductors are ever truly the same lenghth ?
    I think not.

    Especially if your running 2 seperate conduits.
    Say for instance you pulled in 1 set of conductors in 1 of 2 parallel conduits and cut and terminated both ends of the conductor you just pulled into pipe #1.

    Then turned right aroud and took what you just terminated loose, pulled that wire out of pipe #1 and pulled it back into pipe #2 and tried to reterminate it. I'd almost guarantee they would not fall exactly back into place as it did the first time you terminated it.

    Is there any lee way on the requirement of parallel conductors being the same length?

  2. #2
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    Quote Originally Posted by jap View Post
    Do you feel parallel conductors are ever truly the same lenghth ?
    I think not.

    Especially if your running 2 seperate conduits.
    Say for instance you pulled in 1 set of conductors in 1 of 2 parallel conduits and cut and terminated both ends of the conductor you just pulled into pipe #1.

    Then turned right aroud and took what you just terminated loose, pulled that wire out of pipe #1 and pulled it back into pipe #2 and tried to reterminate it. I'd almost guarantee they would not fall exactly back into place as it did the first time you terminated it.

    Is there any lee way on the requirement of parallel conductors being the same length?
    I typically lay the conductors on the ground and measure them. Funny you should post this though as I have some parallels to install tomorrow and i was wondering how much a given length difference would effect current. Could have done some math but I didnt want to know that badly

  3. #3
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    Quote Originally Posted by electrofelon View Post
    I typically lay the conductors on the ground and measure them. Funny you should post this though as I have some parallels to install tomorrow and i was wondering how much a given length difference would effect current. Could have done some math but I didnt want to know that badly
    Rule of thumb for parallel resistances (for small differences between nominally equal resistances) is that a 1% difference in resistance will cause s 1% imbalance in current. And because of the contributions of the terminations at each end, a 1% difference in length will be less than a 1% difference in branch resistance.

  4. #4
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    Quote Originally Posted by jap View Post
    Do you feel parallel conductors are ever truly the same lenghth ?
    I think not.
    The journeyman I learned under would do his best to make sure they were.

    He would start with equal length conductors, make up one end them move to the other; grab one conductor, see where it needed to land cut it off and land it, save the scrap and use it to measure how much to cut off all the others.

    Then he would weave, bend, curl, cuss, kick the conductors, cuss some more, bend the conductors the other way, curl them around his forearm and stuff them in the panel, cuss, cuss, cuss, pull them out, step on them, cuss some more, stuff them back in, give the ones that needed it another good kick, land and tighten everything. After that we got to go home.

    Sometimes it was before sundown, other times I had to pull the truck around and shine the headlights toward where we were working.

    There is no leeway in the code. Parallel conductors have to be the same length.
    If Billy Idol or John Denver is on your Ipod go and re-evaluate your life.

  5. #5
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    You must have learned from the same guys I did. They were sticklers that all conductors were exactly equal in length. We would pull them out across the parking lot if needed.
    I went on to work for a larger firm and on the first parallel pull the guys just pulled them into the panel and chopped them at the lugs. When I asked why they said "it don't matter...nobody ever checks anyway".
    "My goal is to not screw up so bad that they name the screw up after me!"

  6. #6
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    If 2 pipes rise side by siide vertically up from a Panel then turn horizontally (flat) and travel some distance, then make a horizontal bend to the righ or left , then turn verically down into another panel. there's no way the wire in both pipes could be exactly the same length. The spacing between the pipes themselves and the radius of the outside 90 would make the 2 runs different lengths to begin with, regardless if you tried to keep them the same length where they terminate.

  7. #7
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    The code gives no allowance for the differences in length that will almost always exist in a parallel installation. I guess you could say that the code does not really permit parallel installations.
    Don, Illinois
    "It is the first responsibility of every citizen to question authority." B Franklin

  8. #8
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    Quote Originally Posted by jap View Post
    If 2 pipes rise side by siide vertically up from a Panel then turn horizontally (flat) and travel some distance, then make a horizontal bend to the righ or left , then turn verically down into another panel. there's no way the wire in both pipes could be exactly the same length. The spacing between the pipes themselves and the radius of the outside 90 would make the 2 runs different lengths to begin with, regardless if you tried to keep them the same length where they terminate.
    The conductors do not appear to have the same length where they emerge in the gear no doubt.
    If Billy Idol or John Denver is on your Ipod go and re-evaluate your life.

  9. #9
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    Quote Originally Posted by don_resqcapt19 View Post
    The code gives no allowance for the differences in length that will almost always exist in a parallel installation. I guess you could say that the code does not really permit parallel installations.
    As odd as that sounds that is exactly correct. until the requirement is reworded somehow.

  10. #10
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    We may have to just add a turn here or there in our pipe runs to make the two even out.
    i could see where an even number of horizontal 90d bends in a run might get them closer, but with an odd number of horizontal 90d bends, one would always be longer thaan the other, even if there was no spacing between the pipes. On Verticle 90d Bends not so much

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