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Thread: Parallel Conductors - 1/0 minimum?

  1. #1
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    Parallel Conductors - 1/0 minimum?

    What is this 1/0 minumum wire size for parallel conductors based on? (NEC 310.4) Why can't I go smaller, as long as the conductors are identical?

    Case in point is a 460V 125HP Variable Frequency Drive (VFD) rated for 164 Amps. I am using a 225A circuit breaker that also feeds other panels. The lugs on the drive don't allow a 3/0 wire, but it must be at least 3/0 for the 225A breaker.

    Any thoughts?

  2. #2
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    Re: Parallel Conductors - 1/0 minimum?

    Essco,

    This being a branch circuit for a motor the conductors do not need to be sized to the breaker.

    You may size the conductors to the full load current of the motor you will be running from this VFD.

    Take a look at Table 240.4(G) Specific Conductor Applications and parts II, III, and IV of article 430.

    If you post the motor size you are going to be running (you did not say if you where using the drive to the maximum rated load) we could help you out.

  3. #3
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    Re: Parallel Conductors - 1/0 minimum?

    Conductor size to a VFD is based on the input rating of the drive, not the motor HP.
    See 430.2
    Moderator-Washington State
    Ancora Imparo

  4. #4
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    Re: Parallel Conductors - 1/0 minimum?

    Thanks for the catch Tom. :o

    Bob

  5. #5
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    Re: Parallel Conductors - 1/0 minimum?

    essco: The 1/0 minimum, for paralleling, is based on the resistance of 1/0 is not dramatically affected by a slight difference in length.

    1/0 is like a median size selection.

    Any size of conductors can be paralleled as long as the overcurrent device is not more than the ampacity of one conductor.

  6. #6
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    Re: Parallel Conductors - 1/0 minimum?

    Bennie
    You comments make complete sense but I do not see where 310.4 allows it in this type installation.

    [ October 09, 2003, 06:08 PM: Message edited by: bob ]

  7. #7
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    Re: Parallel Conductors - 1/0 minimum?

    Originally posted by bennie:
    <snip>Any size of conductors can be paralleled as long as the overcurrent device is not more than the ampacity of one conductor.
    You lost me here Bennie-- but that's easy enough

    Please define "one conductor". I think that will do it for me.

    Thanks!

  8. #8
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    Re: Parallel Conductors - 1/0 minimum?

    Check out 310.4, exception NO.2 (c).

    I should have wrote, "single conductor" instead of "one conductor".

    I do agree the section does not apply to this installation, when referencing the specified items.

    Two or more conductors, with the ends connected constitutes one conductor. Leaves it a question as to the acceptability for equipment other than the ones specified.

    [ October 07, 2003, 12:17 AM: Message edited by: bennie ]

  9. #9
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    Re: Parallel Conductors - 1/0 minimum?

    Bennie

    Sometimes you have a perfectly good picture in your head, but you do not give us the reader enough information to understand the point you are trying to make, it is very frustrating because we do respect what you have to say.

    If you are going to take a code issue and dispute it, or try to help us understand it differently, you need to be more specific so as to 'paint' the picture for all of us to see.
    Point in case 310.4

    Pierre

  10. #10
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    Re: Parallel Conductors - 1/0 minimum?

    Pierre: Thanks for bringing this to my attention. I have bought a new book titled "Writing Power for Dummy's"

    I will work on my style.

    Dummy's is referring to me, not to others.

    See, I am already clarifying my writing.

    [ October 07, 2003, 07:46 AM: Message edited by: bennie ]

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