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Thread: Multiwire Branch Ciruits

  1. #1
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    Multiwire Branch Ciruits

    Just a quick question, any input is welcome and very much appreciated. When and how is it legal according to the 2017 NEC to use 12/3 NM-B cable for multiple receptacle or lighting circuits in a residential setting?
    Thanks.

  2. #2
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    Quote Originally Posted by Ondarc View Post
    Just a quick question, any input is welcome and very much appreciated. When and how is it legal according to the 2017 NEC to use 12/3 NM-B cable for multiple receptacle or lighting circuits in a residential setting?
    Thanks.
    Perfectly legit. However you would not want to. Ask yourself how are you going to AFCI the circuits? 2 pole AFCI are expensive. Some manufactures allow single pole to be used and they will need to be handle Tied.

    I would not it just complicates things.

  3. #3
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    Did someone tell you that it was not allowed?

  4. #4
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    Quote Originally Posted by Sierrasparky View Post
    Perfectly legit. However you would not want to. Ask yourself how are you going to AFCI the circuits? 2 pole AFCI are expensive. Some manufactures allow single pole to be used and they will need to be handle Tied.

    I would not it just complicates things.
    But can you not use 12/3 on tied single pole breakers?

    Sent from my SM-N910V using Tapatalk

  5. #5
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    Anytime you wish to do so, as long as you meet some requirements.

    210.4 Multiwire Branch Circuits.
    (A) General. Branch circuits recognized by this article shall
    be permitted as multiwire circuits. A multiwire circuit shall be
    permitted to be considered as multiple circuits. All conductors
    of a multiwire branch circuit shall originate from the same
    panelboard or similar distribution equipment.
    Informational Note No. 1: A 3-phase, 4-wire, wye-connected
    power system used to supply power to nonlinear loads may
    necessitate that the power system design allow for the possibility
    of high harmonic currents on the neutral conductor.
    Informational Note No. 2: See 300.13(B) for continuity of
    grounded conductors on multiwire circuits.
    (B) Disconnecting Means. Each multiwire branch circuit shall
    be provided with a means that will simultaneously disconnect
    all ungrounded conductors at the point where the branch
    circuit originates.

  6. #6
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    Only where disconnecting means uses 2-pole breaker, or handle ties across single poles, 210.4(B)

    Not allowed where devices can interrupt neutral continuity (without pigtails), 300.13(B)

    Not allowed for stand-alone power systems (Off Grid Solar Arrays, Batteries, or Generators), 710.15(C)

    See all restrictions by searching the 2017 NPFA-70 PDF for keyword "multiwire"
    Roger Ramjet NoFixNoPay

  7. #7
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    Quote Originally Posted by HappElectrician View Post
    But can you not use 12/3 on tied single pole breakers?

    Sent from my SM-N910V using Tapatalk
    Yes you can use 12/3 or 14/3 as long as the breakers have a handle tie and of course are not on the same phase. I did not state the obvious as we are all supposed to know that you cannot have both circuits on the same phase.

    Quote Originally Posted by packersparky View Post
    Anytime you wish to do so, as long as you meet some requirements.

    210.4 Multiwire Branch Circuits.
    (A) General. Branch circuits recognized by this article shall
    be permitted as multiwire circuits. A multiwire circuit shall be
    permitted to be considered as multiple circuits. All conductors
    of a multiwire branch circuit shall originate from the same
    panelboard or similar distribution equipment.
    Informational Note No. 1: A 3-phase, 4-wire, wye-connected
    power system used to supply power to nonlinear loads may
    necessitate that the power system design allow for the possibility
    of high harmonic currents on the neutral conductor.
    Informational Note No. 2: See 300.13(B) for continuity of
    grounded conductors on multiwire circuits.
    (B) Disconnecting Means. Each multiwire branch circuit shall
    be provided with a means that will simultaneously disconnect
    all ungrounded conductors at the point where the branch
    circuit originates.

    Thanks

    Quote Originally Posted by ramsy View Post

    Not allowed for stand-alone power systems (Off Grid Solar Arrays, Batteries, or Generators), 710.15(C)

    See all restrictions by searching the 2017 NPFA-70 PDF for keyword "multiwire"
    I don't see where stand alone power system is relevant to this topic?

  8. #8
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    Quote Originally Posted by Sierrasparky View Post
    Yes you can use 12/3 or 14/3 as long as the breakers have a handle tie and of course are not on the same phase. I did not state the obvious as we are all supposed to know that you cannot have both circuits on the same phase.




    Thanks



    I don't see where stand alone power system is relevant to this topic?
    Maybe the residence in question is off-grid?

  9. #9
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    Quote Originally Posted by Sierrasparky View Post
    Yes you can use 12/3 or 14/3 as long as the breakers have a handle tie and of course are not on the same phase. I did not state the obvious as we are all supposed to know that you cannot have both circuits on the same phase.




    Thanks



    I don't see where stand alone power system is relevant to this topic?
    Thx. I'm new here, and learning.

    Sent from my SM-N910V using Tapatalk

  10. #10
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    A word of advice--- "Don't use a multiwire branch circuit in a residence"..... It can cause more problems than it's worth. Before the afci were required the multiwire branch circuit was fairly common but you don't see it done anymore
    They say I shot a man named Gray and took his wife to Italy
    She inherited a million bucks and when she died it came to me
    I can't help it if I'm lucky



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