Results 1 to 24 of 24
  1. #1
    Join Date
    Feb 2010
    Location
    Wenatchee Wa
    Posts
    301

    Default Multi-Wire Branch circuit on same leg

    Hey all,

    Ran into a multi-wire branch circuit on same leg in the panel. Since this is on one leg you have a cumulative effect on the neutral.

    I was not able to find anything in the NEC that says this is not allowed other than common sense say bad idea and that you want to size the neutral in accordance of the load.

    Anyone have in more info to share on this?

    Similar Threads:
    Inspection Referral SOC
    Don Hester
    NCW Home Inspections, LLC
    Wa. St. Licensed H I #647, WSDA #80050, http://www.ncwhomeinspections.com

  2. #2
    Join Date
    Aug 2008
    Location
    Maryland
    Posts
    1,899

    Default Re: Multi-Wire Branch circuit on same leg

    You are correct that this will create an additive current on the neutral and could potentially overload it. Worst case it could be carrying 2x the rated current of the circuit.

    The current NEC requires the conductors of a MWBC to be grouped on a 2 pole breaker.

    All answers based on unamended National Electrical codes.

  3. #3
    Join Date
    Mar 2009
    Location
    Colorado Front Range
    Posts
    601

    Default Re: Multi-Wire Branch circuit on same leg

    There are two code violations. The neutral would be undersized, and the ungrounded conductors would be considered paralleled.

    Occam's eraser: The philosophical principle that even the simplest solution is bound to have something wrong with it.

  4. #4
    Join Date
    Feb 2009
    Location
    Southern Vancouver Island
    Posts
    4,549

    Default Re: Multi-Wire Branch circuit on same leg

    I thought I saw this not too long ago, because the breakers were not adjacent to each other. But looking at the panel diagram, it turned out to be OK. The tandem breakers can fool you.

    The problem with my setup was no tie-bar and no way to install a factory tiebar.

    ***IMPORTANT*** You Need To Register To View Images ***IMPORTANT*** You Need To Register To View Images
    John Kogel, RHI, BC HI Lic #47455
    www.allsafehome.ca

  5. #5
    Join Date
    Feb 2010
    Location
    Wenatchee Wa
    Posts
    301

    Default Re: Multi-Wire Branch circuit on same leg

    I should of mentioned this was on a tandem breaker.

    Don Hester
    NCW Home Inspections, LLC
    Wa. St. Licensed H I #647, WSDA #80050, http://www.ncwhomeinspections.com

  6. #6
    Join Date
    Aug 2008
    Location
    Maryland
    Posts
    1,899

    Default Re: Multi-Wire Branch circuit on same leg

    Some tandems will allow the two circuits to be on opposite legs in the panel. IIRC GE is one, most of the other brands do not catch both legs.

    All answers based on unamended National Electrical codes.

  7. #7
    Join Date
    Feb 2010
    Location
    Wenatchee Wa
    Posts
    301

    Default Re: Multi-Wire Branch circuit on same leg

    Thanks Jim this was a Square D so on single leg.

    Don Hester
    NCW Home Inspections, LLC
    Wa. St. Licensed H I #647, WSDA #80050, http://www.ncwhomeinspections.com

  8. #8
    Join Date
    Jul 2008
    Location
    Snowbird (this means I'm retired and migrate between locations), FL/MI
    Posts
    4,086

    Default Re: Multi-Wire Branch circuit on same leg

    Quote Originally Posted by Don Hester View Post
    Thanks Jim this was a Square D so on single leg.
    A modern CTL Square-D tandem Listed Breaker, listed use in a Square-D Listed panel? I don't think so.

    Please provide frame type/size and specific identifying information on the breaker, panel or combo equipment, and buss'

    Thanks.


  9. #9
    Join Date
    Aug 2008
    Location
    Maryland
    Posts
    1,899

    Default Re: Multi-Wire Branch circuit on same leg

    Quote Originally Posted by H.G. Watson, Sr. View Post
    A modern CTL Square-D tandem Listed Breaker, listed use in a Square-D Listed panel? I don't think so.

    .
    I don't see why not.

    All answers based on unamended National Electrical codes.

  10. #10
    Join Date
    Feb 2010
    Location
    Wenatchee Wa
    Posts
    301

    Default Re: Multi-Wire Branch circuit on same leg

    This was a xxxx4040 panel so no tandem would be allowed.

    I was after code info on having a MWBC on the same leg. When I read the NEC I was not clear so I threw it out to the masses to get some perspective and possible code reference that states thy must be on different legs.

    Don Hester
    NCW Home Inspections, LLC
    Wa. St. Licensed H I #647, WSDA #80050, http://www.ncwhomeinspections.com

  11. #11
    Join Date
    Aug 2008
    Location
    Maryland
    Posts
    1,899

    Default Re: Multi-Wire Branch circuit on same leg

    Correct on the no tandem Don.

    All answers based on unamended National Electrical codes.

  12. #12
    Robert Meier's Avatar
    Robert Meier Guest

    Default Re: Multi-Wire Branch circuit on same leg

    Quote Originally Posted by Bill Kriegh View Post
    There are two code violations. The neutral would be undersized, and the ungrounded conductors would be considered paralleled.
    The ungrounded conductors would have to be connected together at both ends to be considered parallel conductors.

    Also as mentioned, running one larger neutral would not be permitted for this type of circuit.


  13. #13
    Join Date
    Mar 2007
    Location
    Ormond Beach, Florida
    Posts
    26,252

    Default Re: Multi-Wire Branch circuit on same leg

    - 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.
    - - - FPN: 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.
    - - (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.
    - - (C) Line-to-Neutral Loads. Multiwire branch circuits shall supply only line-to-neutral loads.
    - - - Exception No. 1: A multiwire branch circuit that supplies only one utilization equipment.
    - - - Exception No. 2: Where all ungrounded conductors of the multiwire branch circuit are opened simultaneously by the branch-circuit overcurrent device.
    - - - - FPN: See 300.13(B) for continuity of grounded conductor on multiwire circuits.
    - - (D) Grouping. The ungrounded and grounded conductors of each multiwire branch circuit shall be grouped by wire ties or similar means in at least one location within the panelboard or other point of origination.
    - - - Exception: The requirement for grouping shall not apply if the circuit enters from a cable or raceway unique to the circuit that makes the grouping obvious.

    - Branch Circuit, Multiwire. A branch circuit that consists of two or more ungrounded conductors that have a voltage between them, and a grounded conductor that has equal voltage between it and each ungrounded conductor of the circuit and that is connected to the neutral or grounded conductor of the system.

    If the multiwire branch circuit is connected to the same bus, it will not have voltage between the ungrounded conductors, and as this is a requirement by definition, the circuit would not be a multiwire branch circuit, it would be an incorrectly wired circuit.

    Jerry Peck, Construction / Litigation Consultant
    Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
    www.AskCodeMan.com

  14. #14
    Garry Blankenship's Avatar
    Garry Blankenship Guest

    Default Re: Multi-Wire Branch circuit on same leg

    I saw a reply indicating they could still be on separate legs. When you see this just check w/ an elec. meter that reads the voltage. One lead on each C/B termination. If no voltage, you are right about the neutral overload potential / incorrect installation. If 240 volts, it's OK. A handle tie is not necessarily required, if two separate 120 volt circuits and installed before that requirement. Still a good idea to have and recommend the tie though.


  15. #15
    Join Date
    Apr 2009
    Location
    NY State
    Posts
    440

    Default Re: Multi-Wire Branch circuit on same leg

    Quote Originally Posted by Don Hester View Post
    I should of mentioned this was on a tandem breaker.
    I see this ALL the time. Very common DIY mistake.


  16. #16
    Join Date
    Feb 2010
    Location
    Wenatchee Wa
    Posts
    301

    Default Re: Multi-Wire Branch circuit on same leg

    Jerry, Thank you that was what I was looking for and missed.

    Thanks all for the comments.

    Don Hester
    NCW Home Inspections, LLC
    Wa. St. Licensed H I #647, WSDA #80050, http://www.ncwhomeinspections.com

  17. #17
    Robert Meier's Avatar
    Robert Meier Guest

    Default Re: Multi-Wire Branch circuit on same leg

    Prior to the 2011 NEC there was nothing to prohibit an over-sized neutral being used for two circuits on the same phase. 200.4 in the 2011 has changed that. For outdoor location it's explicitly permitted by 225.7(B).

    200.4 Neutral Conductors. Neutral conductors shall not
    be used for more than one branch circuit, for more than one
    multiwire branch circuit, or for more than one set of ungrounded
    feeder conductors unless specifically permitted
    elsewhere in this Code.



  18. #18
    Join Date
    Jul 2008
    Location
    Snowbird (this means I'm retired and migrate between locations), FL/MI
    Posts
    4,086

    Default Re: Multi-Wire Branch circuit on same leg

    Quote Originally Posted by Don Hester
    Ran into a multi-wire branch circuit on same leg in the panel. Since this is on one leg you have a cumulative effect on the neutral.

    I was not able to find anything in the NEC that says this is not allowed other than common sense say bad idea and that you want to size the neutral in accordance of the load.

    Anyone have in more info to share on this?
    Quote Originally Posted by Don Hester
    I should of mentioned this was on a tandem breaker.
    Quote Originally Posted by Don Hester
    ...this was a Square D so on single leg.
    Quote Originally Posted by H.G. Watson, Sr.
    A modern CTL Square-D tandem Listed Breaker, listed use in a Square-D Listed panel? I don't think so.

    Please provide frame type/size and specific identifying information on the breaker, panel or combo equipment, and buss'

    Thanks.
    Quote Originally Posted by Don Hester View Post
    This was a xxxx4040 panel so no tandem would be allowed.
    And there is your (chicken/egg) violation: 110.3.


  19. #19
    Join Date
    Mar 2009
    Location
    Colorado Front Range
    Posts
    601

    Default Re: Multi-Wire Branch circuit on same leg

    Quote Originally Posted by Jerry Peck View Post
    - 210.4 Multiwire Branch Circuits.

    If the multiwire branch circuit is connected to the same bus, it will not have voltage between the ungrounded conductors, and as this is a requirement by definition, the circuit would not be a multiwire branch circuit, it would be an incorrectly wired circuit.
    And hence the facts that the circuit has paralleled non grounded conductors and an undersized neutral - both violations. The circuit not meeting the definition of multiwire doesn't make it a violation, as Jerry points out.

    Occam's eraser: The philosophical principle that even the simplest solution is bound to have something wrong with it.

  20. #20
    Robert Meier's Avatar
    Robert Meier Guest

    Default Re: Multi-Wire Branch circuit on same leg

    Quote Originally Posted by Bill Kriegh View Post
    And hence the facts that the circuit has paralleled non grounded conductors and an undersized neutral - both violations. The circuit not meeting the definition of multiwire doesn't make it a violation, as Jerry points out.

    Bill they are not paralleled unless they're connect together at both ends.


  21. #21
    Join Date
    Mar 2009
    Location
    Colorado Front Range
    Posts
    601

    Default Re: Multi-Wire Branch circuit on same leg

    Quote Originally Posted by Robert Meier View Post
    Bill they are not paralleled unless they're connect together at both ends.
    It may be a stretch, but when you connect a load from each line through the neutral they become connected.

    Occam's eraser: The philosophical principle that even the simplest solution is bound to have something wrong with it.

  22. #22
    Robert Meier's Avatar
    Robert Meier Guest

    Default Re: Multi-Wire Branch circuit on same leg

    Quote Originally Posted by Bill Kriegh View Post
    It may be a stretch, but when you connect a load from each line through the neutral they become connected.

    I've actually heard that one before.


  23. #23
    Join Date
    Oct 2009
    Location
    michigan
    Posts
    421

    Default Re: Multi-Wire Branch circuit on same leg

    Both ungrounded conductors could be tied to the same breaker (if listed for 2) and that would be OK but wouldn't make any sense. I've seen a diy job with this very setup, uggg.

    A fully loaded-all capacitive load on a multi wire branch circuit may require a larger neutral under certain circumstances.

    I have a double tandumdum Siemens breaker in my truck that I bought decades ago thinking it might come in handy. It is setup to install 2 multi wire branch circuits.
    Looks like I'm going to have it when it becomes a collectors' item


  24. #24
    Join Date
    Mar 2007
    Location
    Ormond Beach, Florida
    Posts
    26,252

    Default Re: Multi-Wire Branch circuit on same leg

    - 240.15 Ungrounded Conductors.
    - - (A) Overcurrent Device Required. A fuse or an overcurrent trip unit of a circuit breaker shall be connected in series with each ungrounded conductor. A combination of a current transformer and overcurrent relay shall be considered equivalent to an overcurrent trip unit.
    - - - FPN: For motor circuits, see Parts III, IV, V, and XI of Article 430.
    - - (B) Circuit Breaker as Overcurrent Device. Circuit breakers shall open all ungrounded conductors of the circuit both manually and automatically unless otherwise permitted in 240.15(B)(1), (B)(2), and (B)(3).
    - - - (1) Multiwire Branch Circuit. Except where limited by 210.4(B), individual single-pole circuit breakers, with or without identified handle ties, shall be permitted as the protection for each ungrounded conductor of multiwire branch circuits that serve only single-phase line-to-neutral loads.
    - - - (2) Grounded Single-Phase and 3-Wire dc Circuits. In grounded systems, individual single-pole circuit breakers with identified handle ties shall be permitted as the protection for each ungrounded conductor for line-to-line connected loads for single-phase circuits or 3-wire, direct-current circuits.
    - - - (3) 3-Phase and 2-Phase Systems. For line-to-line loads in 4-wire, 3-phase systems or 5-wire, 2-phase systems having a grounded neutral point and no conductor operating at a voltage greater than permitted in 210.6, individual single-pole circuit breakers with identified handle ties shall be permitted as the protection for each ungrounded conductor.
    - - (C) Closed-Loop Power Distribution Systems. Listed devices that provide equivalent overcurrent protection in closed-loop power distribution systems shall be permitted as a substitute for fuses or circuit breakers.

    Jerry Peck, Construction / Litigation Consultant
    Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
    www.AskCodeMan.com

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •