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  1. #1
    Join Date
    Oct 2011
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    Default Outlet on Two Breakers?

    I recently attempted to replace an outlet and like a good boy I turned off the breaker. Once off, I tested the outlet and it showed that no juice was flowing. Thinking all was well in the world, I went and began replacing and once I got the fourth wire on, I got a zing and the lights flickered that were plugged into outlets on the breaker that was OFF. Any way this can happen?

  2. #2
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    Default Re: Outlet on Two Breakers?

    It's very possible that circuit you shut off at the breaker is part of a Multi Wire Branch Circuit ( MWBC ) which is simply two circuits being fed by individual hot conductors but sharing the same neutral. This can be a dangerous arrangement since the neutral is returning current from the other circuit it shares.

    This is why up here in Canada it's mandatory that all MWBC hot conductors be connected to a double pole common trip breaker -- in your case in the States two single pole breakers connected together with handle ties.

    This way when you want to shut off the circuit you are working on both are disconnected to remove any return current on the shared neutral.
    "" an ounce of perception -- a pound of obscure "
    - Rush

  3. #3
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    Oct 2011
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    Default Re: Outlet on Two Breakers?

    I disconnected the outlet and checked other outlets - all is in working condition. Could I just cap two of the wires coming in and connect the other two? It seems as this is the termination of at least one of the circuits.

  4. #4
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    May 2011
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    Default Re: Outlet on Two Breakers?

    I am not an electrical sage, so excuse me for any errors . . .

    I hate old wiring as modifications made by people because they don't follow color convention, etc., or the installer used whatever was in his parts box.

    First, I don't understand what happened here ? Why would there be "4" wires ?? If I saw more than 2 hot/neutral wires attached an outlet, I would ask why ??

    In a switched outlet, I often would "unswitch" the bottom plug (a 2nd hot tapped from a unswitched hot), but they all would be part of the same circuit.

    I don't know anything about MBC, and why a "4th" wire would be attached to the outlet, especially if he checked that juice wasn't flowing. Was other circuit in the box and the box was an access/junction box for the 2nd circuit, and why would the 2nd circuit wires be handled when replacing the outlet ?

  5. #5
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    Default Re: Outlet on Two Breakers?

    Quote Originally Posted by Brookworld View Post
    I am not an electrical sage, so excuse me for any errors . . .

    I hate old wiring as modifications made by people because they don't follow color convention, etc., or the installer used whatever was in his parts box.

    First, I don't understand what happened here ? Why would there be "4" wires ?? If I saw more than 2 hot/neutral wires attached an outlet, I would ask why ??

    It's quite common to find 4 wires at a receptacle --- basic wiring 101. Say for example --- you have 5 receptacles in a room on the same circuit -- hot and neutral feeding the first receptacle -- hot and neutral from that first receptacle onward to feed the second and so on -- until the 5th receptacle ( end of run ) which would only have 2 wires ( hot and neutral ) . This is commonly referred as daisy-chaining. In other words you have to supply current to each receptacle somehow.


    In a switched outlet, I often would "unswitch" the bottom plug (a 2nd hot tapped from a unswitched hot), but they all would be part of the same circuit.

    I don't know anything about MBC, and why a "4th" wire would be attached to the outlet, especially if he checked that juice wasn't flowing. Was other circuit in the box and the box was an access/junction box for the 2nd circuit, and why would the 2nd circuit wires be handled when replacing the outlet ?
    There's some misunderstanding here --- I'm not saying a second circuit was located here ( though it could be ) but rather two completly different circuits are sharing the same neutral.

    Example --- let's say the lights and receptacles in a room happen to be on seperate circuits ( breakers ) --- it's not uncommon that a 14/3 ran from the panel up to this room is done.

    14/3 or 12/3 cable contains --- red -- black -- white --- conductors.

    In this example -- The red conductor would be the *hot* feed for one circuit ( say the lights ) --- the black conductor would be the *hot* feed for the other circuit ( say the receptacles ).

    However , those 2 seperate cicuits are sharing the same neutral ( since there is only one white wire from the panel ).

    So , in the above example when the breaker is shutoff for the black conductor there is still return current flowing in the white ( neutral ) because the red conductor is still live and shares the white ( neutral ).


    Clear as mud ?
    Last edited by canuk; 10-21-2011 at 09:53 AM.
    "" an ounce of perception -- a pound of obscure "
    - Rush

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