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Thread: The new 2008 NEC code 210.4(B)

  1. #1
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    The new 2008 NEC code 210.4(B)

    The new 2008 210.4 reads:
    210.4 Multiwire Branch 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.
    --------------------------------------------------------------------------
    My understanding:
    For shared neutrals in conduits, all branch circuits shall have disconnecting means via a multipole breaker in the panel it serves from, reguardless of how many poles.

    What if the wires go through a wiring trough or a chase nipple? There are no exceptions. Has this ever been disussed here before?

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    Quote Originally Posted by powersoft View Post
    Has this ever been disussed here before?
    Many times. Do search for MWBC, handle ties, 210.4 etc...

    Roger
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    Let's define you understanding a bit..
    Check the definitions for "branch circuit, multiwire".
    If the circuit qualifies then there must be a common disconnecting means.
    This can be a multi-pole breaker, a handle tie on the circuits involved or another means.

    The rule would apply to the individual MWBC. If you happen to have multiple MWBs in one conduit, each would be addressed separately.
    (For example, you would not need a 6 pole handle tie for (2) MWBC)
    Last edited by augie47; 08-13-10 at 03:05 PM. Reason: Two threads by the same poster were merged
    At my age, I'm accustomed to restaurants asking me to pay in advance, but now my bank has started sending me their calendar one month at a time.

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    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.


    I assume this is because it is in the same condult or jacket. Still no clear cut definition if that includes a wiring trough or chase nipple (in the case of 6" nipple which can feed an adjacent panel). This could be a real problem with AHJ and contractors it seems.

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    Quote Originally Posted by powersoft View Post
    I assume this is because it is in the same condult or jacket. Still no clear cut definition if that includes a wiring trough or chase nipple (in the case of 6" nipple which can feed an adjacent panel). This could be a real problem with AHJ and contractors it seems.

    Huh? I have no idea what you mean.

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    Quote Originally Posted by powersoft View Post
    My understanding:
    All hot wires that are routed in a common conduit, trough (or nipple) shall be protected by a multipole breaker, no matter how many poles are required to accomplish this.
    Go back and read Augie's post again.

    Roger
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    Quote Originally Posted by powersoft View Post
    I assume this is because it is in the same condult or jacket.
    You assume incorrectly. The reason that a common trip (multipole breaker or handle ties) is required has to do with the safety of a maintenance person working in a junction box somewhere along the run. It does not matter whether the wires are run in conduit, in surface mounted raceway, as a multi-conductor cable, or any thing else.

    Charles E. Beck, P.E., Seattle
    Comments based on 2014 NEC unless otherwise noted.

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    Quote Originally Posted by augie47 View Post
    Let's define you understanding a bit..
    Check the definitions for "branch circuit, multiwire".
    If the circuit qualifies then there must be a common disconnecting means.
    This can be a multi-pole breaker, a handle tie on the circuits involved or another means.

    The rule would apply to the individual MWBC. If you happen to have multiple MWBs in one conduit, each would be addressed separately.
    (For example, you would not need a 6 pole handle tie for (2) MWBC)

    Sorry my typeing and my reading are getting a little stretched.

    I guess what really gets me is a staff note i read from necplus.com
    ------------------------------------------------------------------------
    Staff Note for 210.4(B)
    Multiwire branch circuits are frequently used to economize on homerun wiring by sharing a grounded conductor among either two or three phase conductors. For safety, 210.4(B) requires that when a multiwire branch circuit supplies more than one device or equipment on the same yoke (often a duplex receptacle), a multipole circuit breaker or switch or two circuit breakers with a listed handle tie must be used to disconnect all ungrounded conductors. The reason for this requirement is to prevent injury to electricians or others servicing those devices by ensuring that all conductors in the same outlet box are OFF (de-energized).
    -------------------------------------------------------------------------
    Is this the consensus then is a ungrounded wire of a MWBC is anything surounded in a jacket, box or other wiring means beside the panelboard box that serves BESIDES a shared neutral???

  9. #9
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    Seems like you are trying to reinvent the wheel
    Again, the definition:
    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.
    No mention of "jacket, cable,box, etc.
    If you have a circuit with more than one ungrounded conductor and a shared grounded condutor and it meets the above definition, you have a MWBC.
    One that is determined, you need a common disconnecting means for the ungrounded circuits. Makes no difference if they are in a cable, pipe, or free air.
    The "same yoke" rule was prior to the '08 Code whicjh expanded the requirement.
    At my age, I'm accustomed to restaurants asking me to pay in advance, but now my bank has started sending me their calendar one month at a time.

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    PS, welcome to the forum!

    The handle-tie or multi-pole breaker requirement is for each group of two or three hots that share a neutral. For example, a 3-wire (two hots and a neutral) MWBC requires a 2-pole breaker or handle tie.

    Even if two of these 3-wire MWBC's happen to enter the same cable or conduit, each pair of hots that share a neutral must still only have the two poles of each MWBC joined at the handles, nothing more.
    Code references based on 2005 NEC
    Larry B. Fine
    Master Electrician
    Electrical Contractor
    Richmond, VA

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