Objections - code or otherwise of running multiple conductors

Discussion in 'Electrical Forum discussion & Blog' started by ballvalve, Aug 26, 2011.

  1. ballvalve

    ballvalve General Engineering Contractor

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    So a guy has million or so feet of THHW #6 copper. Wants to run about 90 amps to a sub panel in conduit.

    What are code or safety reasons for running 3 or 4 of these seperate conductors per line and connecting them with a in line splice to a large single cable at the panels, or winding and soldering them into a single lead at each breaker connection?

    And if its a no-no in the book, can you say the practical reason why? Besides being a lot of extra labor.

    And try not and simply say don't say trade it for the "right" cable.
  2. jwelectric

    jwelectric Electrical Contractor/Instructor

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    310.4 Conductors in Parallel.
    (A) General. Aluminum, copper-clad aluminum, or copper conductors of size 1/0 AWG and larger, comprising each phase, polarity, neutral, or grounded circuit conductor shall be permitted to be connected in parallel (electrically joined at both ends).

    AS to the question “why” my answer is simple; it is not my place to question why but to do or cry. Which will you be doing?
  3. Jim Port

    Jim Port Electrical Contractor

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    The cost of doing so might outweigh the cost of using the correctly sized conductors even before you factor in the time to do this. You are also introducing another potential fail point. You would also end up using more conduit for the parallel run.

    Oh ya, like Mike already said, #6 is too small to be code compliant paralleled.
  4. ballvalve

    ballvalve General Engineering Contractor

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    Okay. So the answer is if its less than 1/0 its not compliant to join up multiple smaller conductors...

    I get the time factor clearly, but can you guys say if practically speaking you see any dangers other than the introduction of fail points?

    Of course I ask you to go beyond the book, just to clear up for me if these smaller multiple conductors create some sort of danger in their "seperate" and parallel state.

    If 5] 1/0 conductors ganged up work, why not 10] 6 guage?
  5. jwelectric

    jwelectric Electrical Contractor/Instructor

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    It would get really in depth with math to explain why the cut off is set at 1/0 in most cases for paralleling conductors.

    The easy answer would be due to heat should there be a difference in length of as little as ½ inch. A difference in the amount of torque used to terminate each conductor and the list goes on and on. Then we have the inductance between the conductors both inductive and capacitive. Magnitude and time is also a factor. As you can see one would need to be well versed in physics and calculus in order to fully understand why.
    A series circuit divides voltage and a parallel circuit divides current. In the paralleling of conductors the resistance of each conductor must be the very same for each conductor to draw the same amperage and this is impossible. The smaller the conductor the less abuse it can withstand due to heat so 1/0 is the general rule for paralleling conductors

    When we search for a reason to justify something we don’t fully understand there is a simple rule I state. “It is not my place to question why just to do or cry.†If I don't know the answer to a question such as the one you ask here then there is no need for me to question the rule as those with greater minds have already found the answer before me therefore we have the rule.

    A few years back I saw the engineer’s paper work on a set of parallel conductors for a pump at a water treatment plant. This was 4160 volts with a 300hp motor. The formula for the conductors was written on a legal pad and it was three pages of a bunch of numbers and letters some in [] and some in (). There was a bunch over the top of others and some that were in [()]
    As I looked down at all that mess it reminded me of the time I was painting the carport and the chickens got into my roller pan and walked across the floor scratching here and there.
    While I was standing there with tears rolling down my cheek the thought came to me and I grabbed one of them wires and took off running, don’t question why just do it was my conclusion.

    Yes there is a safety issue or the rule would not be there. Remember the NEC is a minimum safety book and to do anything less means it is unsafe.
  6. ballvalve

    ballvalve General Engineering Contractor

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    Location:
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    Thanks for the start of a practical reply, but I suspect the real answer is that no one has tested such a circuit.

    My replay was either deleted or lost, and if deleted, it makes this a very sad place to post indeed.

    This is not an electrical forum, it is a code quoting blog with big, no questions of "law" blinders. I'll get the kids at the science fair to set up and test such a circuit under load and report back [for deletion] if any issues of safety were detected.

    A lot of posters here have the same feeling as you did when your chickens painted your carport, when they read your attacks on their questions.
  7. jwelectric

    jwelectric Electrical Contractor/Instructor

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    Location:
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    I am not aware of your post being deleted. The answer I gave was my professional opinion on the matter not something that you wanted to hear evidently.

    Paralleling of conductors less than 1/0 has most certainly been tested by educated electrical engineers and in some cases is even allowed but not as you suggest.

    The NEC is a consensus of standards that are constantly ongoing and changing as technology changes. Every three years the NEC is updated based on the findings of consensus from all around the world.

    Feel free to make a proposal to allow the paralleling of #6 conductors if you think it would be alright to parallel them. In order to get a rule changed it needs a substantiation of the reason for changing.

    You can’t solder the conductors together and land the mess under a screw of a breaker either. The screw at the breaker is listed for one and sometime two conductors not something such as you are suggesting.

    Where have I attacked your question?
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