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Thread: 14/3 strange usage

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  1. #1
    DIY Junior Member MrBillyd's Avatar
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    Default 14/3 strange usage

    I am in the middle of demo and rebuild of 40 feet of softit removal and raising all of my ceiling up to 8ft.
    The house was built in 79.
    I have been re working the existing wiring so I can reinstall all the dry wall.
    I found two strange usages of 14/3.
    The home builder ran 14/3 for two different circuts instead of running 2 14/2.
    So, instead of running 80 feet across the house with 2 14/2 he ran one 14/3 and shared the N.
    In the living room the red hot wire goes thur a light switch to control a plug.
    The black controls the other 4 outlets, garage lighting, door opener, utility rm lights, kitchen, hallway and entry way lights.
    (Today I ran 2 new 14/2 feeds removing garage's 5 items, and another removing the utility and kitchen.)

    Another situation they did this was in the kitchen, (same idea but with 12 awg wire) Red wire feeds the disposal, black the dishwasher and the counter outlets.
    Does this type of shared N still happen today?

    Also, I just bought a GFI outlet as my kitchen does not have one. Can you use a GFI with a circuit that has a shared N ?
    Or will turing on the disposal trigger a GfI on the other circuit?

    Thanks
    Bill

  2. #2
    Electrician ActionDave's Avatar
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    Quote Originally Posted by MrBillyd View Post
    .... instead of running 80 feet across the house with 2 14/2 he ran one 14/3 and shared the N....
    Another situation they did this was in the kitchen, (same idea but with 12 awg wire) Red wire feeds the disposal, black the dishwasher and the counter outlets.
    Does this type of shared N still happen today?
    It is called a Multi-wire Branch Circuit. Yes they are legal, common, and still used today.

    Also, I just bought a GFI outlet as my kitchen does not have one. Can you use a GFI with a circuit that has a shared N ?.....

    Thanks
    Bill
    You can, but knowing how and where in the circuit to hook them up is a bit tricky. How brave are you?

  3. #3
    DIYer, not in the trades LLigetfa's Avatar
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    It's common to see kitchen split receptacles fed from a ganged breaker.

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    Plumber jimbo's Avatar
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    You have to be careful with the neutrals. I was once baffled for a while by a GFI trip...someone had tied some whites together in a box where a receptacle was fed from the GFI load side. That neutral from a different "hot" leg added an unbalanced flow back to the GFI and tripped it.

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    Moderator & Master Plumber hj's Avatar
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    The shared neutral is ONLY legal when the two "hot" legs are on different sides of the incoming service. If they are on the same side, the amp loads on the neutral are added together instead of subtracted.
    Licensed residential and commercial plumber

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    Quote Originally Posted by hj View Post
    The shared neutral is ONLY legal when the two "hot" legs are on different sides of the incoming service. If they are on the same side, the amp loads on the neutral are added together instead of subtracted.
    Explain this in detail HJ. Thanks for the post. I'm taking it as when you install the breakers for the two circuits(one 14/3 or 12/3 etc) one breaker should be on one side of the panel and the other breaker should be on the opposite side,corresponding to the two incoming feeds from the utility co.

  7. #7
    Electrical Contractor/Instructor jwelectric's Avatar
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    Quote Originally Posted by Hackney plumbing View Post
    Explain this in detail HJ. Thanks for the post. I'm taking it as when you install the breakers for the two circuits(one 14/3 or 12/3 etc) one breaker should be on one side of the panel and the other breaker should be on the opposite side,corresponding to the two incoming feeds from the utility co.
    The breakers should be installed side by side so a handle tie will cause both breakers to turn off at the same time. This is a requirement of the new NEC.

    If using a multi-wire circuit and you are a DIYer it would be a real good idea to use a two pole breaker for this circuit. This way you can’t go wrong.



    look at the bus bars of the CH panel. You can see that one breaker straight across form the other would be on the same leg but two breakers side by side would land on two legs of the panel.
    When installing a multi-wire circuit it is important to be sure that the breakers land on opposing legs so the unblanced load is carried on the neutral. If both breakers are on the same leg the current adds on the neutral which will cause the insulation of the neutral to melt.

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    I see that when the breakers are aligned horizontally they would share the same leg of the supply but when installed "stacked" vertically directly above and below each other they are on seperate legs. The panel alternates. So let me get this straight about the principle of it.......since both circuits share the neutral and the neutral is the return path of a.c. current,the shared neutral would be the return path for both circuits and thats an overload aka "A house fire" LOL

    What I really dont understand is why installing the breakers on different legs of the panel would prevent that.... I guess it's balanced that way? Thats the part I strugggle wit I think.

    Thanks for your time. I dont plan on doing any wiring but its nice to learn. By the way,if this is such an issue why is it a new code? Seems like it would have been code long ago seeing it can burn houses down.
    Last edited by Hackney plumbing; 02-21-2012 at 09:44 AM.

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