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  1. #1
    Join Date
    May 2010
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    Default MWBC & GFCI question

    Hi folks!

    I have a hopefully easy (but probably not) question for y'all. Forgive my being verbose - just trying to provide the necessary information.

    I recently purchased a foreclosed home; it was built in 1974 and has had a couple new additions put on and has been remodeled a time or two. The result is that the simplest of tasks here often turns into a major project to fix the mistakes of DIYers who traded 'get it done right' for 'get it done'.

    During a recent attempt to simply install a 3-way switch, I found that someone had extended one of my 20A kitchen receptacle circuits using 14AWG wire. I traced back the 14 and disconnected it, effectively orphaning 3 receptacles. I'm OK with 2 of them not functioning - they're in the way of a future French door anyway - but I would like to restore one.

    This one is in a 2-gang box with the switch that controls my garbage disposal. There is a MWBC running into this box via a 12-3 cable.

    One branch handles the garbage disposal and the dishwasher. The black live is connected to a switch & a second ("downstream") 12-3. The live on the source 12-3 goes directly to the receptacle, providing always-on power to the dishwasher. The red from the downstream 12-3 connects the switch to the receptacle, allowing that plug - and the disposal - to be powered on/off via the switch.

    The other branch appears to go out to my patio and controls 3 ceiling fan/light fixtures and 2 dry receptacles. The red is live from the source. The neutral is wirenutted into the all of the neutrals from the other branch. The live red is wirenutted to a black wire in 12-2 cable. The black then heads out to power 3 ceiling fan/light fixtures and 2 dry receptacles in my patio area.

    The three neutrals (from the source 12-3, the downstream 12-3, and the 12-2 out) are wirenutted together, as are the grounds.
    -----------------------------

    My 1st question: can I put the orphaned receptacle on the 2nd brance of this circuit? I know code requires 2 20A circuits for countertop appliances, and I have those. Putting this receptacle would be bringing a 3rd 20A circuit into the kitchen. Having met code already, is it okay to have a kitchen receptacle on a circuit that is shared with outside devices?

    My 2nd question is this: because this outlet will be in the kitchen, I want it to be GFCI protected. Can I install a GFCI receptacle on a circuit with a shared neutral? If I can, my plan would be to put the live red into the hot line, the black into the hot load, and then create two neutral pigtails to go into the neutral bundle. And, naturally, I'd pigtail a ground into the all the other grounds.

    Third question: if I cannot put a GFCI receptacle on this circuit, what are my options for getting GF protection? I assume I can always replace the breakers (currently double pole) with a GFCI double pole. Any other options?

    Any input and feedback would be greatly appreciated. And again: apologies for the loooooooong post.
    Last edited by kttyracing; 05-15-2010 at 06:08 PM. Reason: Updated description of wiring

  2. #2
    Join Date
    May 2010
    Location
    Phoenix, AZ
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    13

    Default Re: MWBC & GFCI question

    Doing a little more research, it sounds like I >can< put a GFCI on the 2nd circuit provided that the shared neutral is upstream (i.e. before the line input) of the GFCI. Is this correct?

    Based on this, I assume my neutral wiring would be as follows:

    Source 12-3 wirenutted to downstream 12-3 (going to the dw/gd outlet) and a pigtail to the GFCI neutral line.

    12-2 - controlling the fans & such - connected to the GFCI neutral load.


    Thoughts?
    Last edited by kttyracing; 05-15-2010 at 06:09 PM. Reason: Updating wiring description

  3. #3
    Join Date
    Jun 2007
    Location
    Shamokin, Pa.
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    645

    Default Re: MWBC & GFCI question

    Quote Originally Posted by kttyracing View Post
    Doing a little more research, it sounds like I >can< put a GFCI on the 2nd circuit provided that the shared neutral is upstream (i.e. before the line input) of the GFCI. Is this correct?

    Based on this, I assume my neutral wiring would be as follows:

    Source 12-3 wirenutted to downstream 12-3 (going to the dw/gd outlet) and a pigtail to the GFCI neutral line.

    12-2 - controlling the fans & such - connected to the GFCI neutral load.


    Thoughts?
    You may have to draw all that out. I have found that sharing a neutral is never a good idea.

  4. #4
    Join Date
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    The Great White North
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    Default Re: MWBC & GFCI question

    Quote Originally Posted by deadshort View Post
    I got really dizzy reading the OP so will refrain from a reply.
    try reading that after a few beers and slings.
    "" an ounce of perception -- a pound of obscure "
    - Rush

  5. #5
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    Default Re: MWBC & GFCI question

    Singapore Sling ?!?
    "" an ounce of perception -- a pound of obscure "
    - Rush

  6. #6
    Join Date
    Aug 2007
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    Default Re: MWBC & GFCI question

    Considering the name " Singapore " would lead one to believe it's not an Inuit name --- and here I always looked to you as being the worldly , wise and powerful one --- knower and see'er of all --- please say it isn't so
    "" an ounce of perception -- a pound of obscure "
    - Rush

  7. #7
    Join Date
    Sep 2009
    Location
    jersey
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    174

    Default Re: MWBC & GFCI question

    yes to everything except being able to use a 2 pole gfi breaker with one nuetral. IME the only ones that really work right are the cutler hammer type ch independent trip. I would use gfi devices here in place of the gfi breakers. Assuming I understood you correctly.
    Help us name our new Hidden Content

  8. #8
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    Default Re: MWBC & GFCI question

    Yes , the blossoms are just about ready to explode into that amazing canopy of colour. Thanks to an unseasonable warm April --- which put us a month ahead. Today was a glorious and beautiful day for example --- even June like.

    --- oh and thanks for the identification of that tree --- by the way.
    "" an ounce of perception -- a pound of obscure "
    - Rush

  9. #9
    Join Date
    May 2010
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    Phoenix, AZ
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    13

    Default Re: MWBC & GFCI question

    Thank you, Ernie and Lloyd, for taking the time to offer your input. I appreciate it.

    As requested, here are some rough'n'dirty diagrams of the current state ('Circuit Diagram Current.jpg') and what I'd like to do ('Circuit Diagram Future.jpg').

    Hopefully the peanut gallery can cut a girl some slack and not harangue the quality of the sketches.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

Name:	Circuit Diagram Current.jpg 
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ID:	3519   Click image for larger version. 

Name:	Circuit Diagram Future.jpg 
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ID:	3520  

  10. #10
    Join Date
    Jun 2007
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    Fayette County, Ohio
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    5,842

    Default Re: MWBC & GFCI question

    To the OP, in theory yes you can providing you replace the 14-2 with 12-2. However, because a GFCI is always providing a load on the circuit,I believe you will end up with a lot of false trips.
    Jack
    Be sure you live your life, because you are a long time dead.-Scottish Proverb

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