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Thread: larger wire for voltage drop

  1. #1
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    larger wire for voltage drop

    Theres a circuit pulling 24 amps and is about 400 feet long.
    The wire size gets increased to #4 copper to reduce resistance and voltage drop.
    Now the wire will not fit into the breaker so here is my questions.

    1)If several strands are removed from the wire to fit on the breaker would the strands that are cut in the wire be of no use in reducing resistance even tho they are in contact with all the other strands tightly wrapped in insulation.

    2)If no strands are cut on the #4 and Butt splices are used to reduce the wire down to a size that will fit on the breaker will there be less resistance in the circuit than if the strands are cut?

    All thoughts welcome

  2. #2
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    dont cut strands or but splice to smaller wire. put in new lugs for the size of wire

  3. #3
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    Never cut the strands of a conductor if for no other reason then it screams 'hack'.

    You can splice on a smaller conductor as long as the smaller conductor is still above the ampacity of the breaker and the load being placed n it.

    10' of 'normal' size wire at the end of 400' of up sized wire will not effect voltage drop enough to worry about, do the calculations and you can prove it.

  4. #4
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    Quote Originally Posted by var View Post
    Theres a circuit pulling 24 amps and is about 400 feet long.
    The wire size gets increased to #4 copper to reduce resistance and voltage drop.
    Don't forget to increase the EGC based on 250.122(B). Sorry I had to do that. :smile:

  5. #5
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    Quote Originally Posted by var View Post
    Theres a circuit pulling 24 amps and is about 400 feet long.
    The wire size gets increased to #4 copper to reduce resistance and voltage drop.
    Now the wire will not fit into the breaker so here is my questions.

    1)If several strands are removed from the wire to fit on the breaker would the strands that are cut in the wire be of no use in reducing resistance even tho they are in contact with all the other strands tightly wrapped in insulation.

    2)If no strands are cut on the #4 and Butt splices are used to reduce the wire down to a size that will fit on the breaker will there be less resistance in the circuit than if the strands are cut?

    All thoughts welcome
    I'm with the others here. Don't cut any strands out.
    We often come across issues where the conductors are too large or numerous to fit on to breaker terminals. There are various solutions. One is to "extend" the terminals. Here's one we did earlier.


  6. #6
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    Quote Originally Posted by Besoeker View Post
    I'm with the others here. Don't cut any strands out.
    We often come across issues where the conductors are too large or numerous to fit on to breaker terminals. There are various solutions. One is to "extend" the terminals. Here's one we did earlier.
    Wow, sorry, but I don't like that conversion one bit. Would 4 barrel lugs been a better choice?
    Last edited by charlie b; 07-08-09 at 10:49 AM. Reason: To remove the unnecessary extra copy of the photo.

  7. #7
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    There wasnt an answer to the question 1.
    The reason I asked the question was I came across this situation.
    I measured voltage drop at the customers equipment, I then repaired the cut strands and spliced a piece of #8 to land on the breaker, "I understand that I was lowering resistance and that a small section wouldnt matter".
    My thought was that the strands being cut werent being used in the larger cable to lower resistance because they werent connected at both ends.
    So I made the splices, fired up the equipment and there was no difference in the voltage at the equipment at all.
    The customer then informed me it was a waste of time and money to do that.
    I explained my reasoning but he didnt really care.
    I'm just trying to understand how the cut strands still lowered resistance even tho they werent connected.

  8. #8
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    I do not understand the situation you encountered, nor your repair, nor the test you did after your repair. But I will try to answer your first question.

    I am sure that you know that if you put two resistors in series, the total resistance gets higher, and is equal to the sum of the two resistances. If you put five identical resistors in series, then the total resistance is equal to five times the value of any one of them. If you make a series connection of resistors that are of different values, then you simply add up the individual values to get the total resistance.

    A long conductor can be regarded as a series connection of small resistors. Consider a 1 foot long section of #4 bare copper wire. It has some value of resistance. Now consider a 100 foot long section of the same wire. It is essentially a series connection of 100 resistors, each having the value of resistance as your initial 1 foot section, and the total resistance is 100 times the value of the 1 foot section. If you tie together (good luck on getting good connections here, but stay with me, and let’s pretend you can do this with zero extra resistance at the connection points) 100 sections of 1 foot long bare wires of varying AWG sizes, then the total resistance will be the sum of the resistances of the one hundred individual pieces.

    In your example, you have 399 feet plus 11 inches of #4 wire in series with a 1/2 inch section of #4 wire that has been trimmed down and placed into a lug on one end, plus another 1/2 inch section of #4 wire that has been trimmed down and placed into a lug on the other end. This is a total of three resistors in series, and the total resistance is the sum of the three individual resistances. The resistance per unit length of the trimmed down sections at either end is higher than the resistance per unit length of the long section. But the total resistance of the 399+ foot long piece in the middle has not been altered by what was done at either end.

    Does this answer your question?

    By the way, welcome to the forum.
    Last edited by charlie b; 07-08-09 at 10:50 AM.
    Charles E. Beck, P.E., Seattle
    Comments based on 2014 NEC unless otherwise noted.

  9. #9
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    Thanks Charlie,
    Yes, that makes things a bit more clearer now.
    My customer had a piece of equipment that would not run at lower than 230 volts.
    A contractor came and upsized the wire for voltage drop but then trimmed the ends to fit under the lugs at disco and at the breaker.
    I told the customer that it shouldnt have been done like that and it would lower the resistance of the run to remove the trimmed #4 ends and splice a #8 smaller piece on the #4 ends untrimmed with butt splices and that we should gain a couple volts in doing so.
    I measured the voltage at the equipment at full load amps before I removed the trimmed pieces and after I made the repair with #8 wire at the disco and breaker and there was no difference.
    I guess I didnt understand how the trimmed strands would count as lowering the resistance when they were not connected at either end, but they must count because they are wrapped tightly with the other strands and held tight by the insulation.

  10. #10
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    Quote Originally Posted by var View Post
    I guess I didnt understand how the trimmed strands would count as lowering the resistance when they were not connected at either end, but they must count because they are wrapped tightly with the other strands and held tight by the insulation.
    That is correct, just because they are not connected by the terminal the cut strands still function.

    In my opinion you corrected a code violation.

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