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Thread: Confused on GFCI, AFCI or just status quo in the kitchen

  1. #1
    Senior Robin Hood Guy Ian Gills's Avatar
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    Default Confused on GFCI, AFCI or just status quo in the kitchen

    The receptacles in my kitchen were wired wrongly ever since I moved into my house and it has bugged me.

    There are two 20 amp circuits in question that run a couple of receptacles on either side of the sink, the garbage disposal, dishwasher and the fridge.

    I want to fix the things that I am unhappy with.

    First, the two circuits share a neutral and I know there is nothing wrong with this per se, but I don't like shared neutrals, in the same way Americans do not like ring mains. So that has to go.

    Secondly, and worse, the 12-3 cable used for the shared neutral has been stabled under sections of joists (rather than through holes bored in them) and that is a no-no.

    My dilemma is this. At the moment, the circuit is protected by two 20 amp circuit breakers. Those receptacles within 6 feet of the sink are GFCI-type and the others are not.

    So, should I replace the two 20 amp cicruit breakers with two 20 amp GFCI combination circuit breakers; or, can I use the two 20 amp AFCI combination circuit breakers I have lying around.

    Or is this all overkill and should I do nothing and keep my existing 20 amp breakers?
    Last edited by Ian Gills; 09-12-2009 at 08:55 PM.

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
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    Not sure how those with the shared neutral work in GFCI circuits...

    An AFCI isn't the same thing nor will it provide the desired protection as a GFCI. The AFCI detects arcs that could cause fires and then trips. The GFCI detects leakage current that might be going through you that could kill you.

    I suppose the fire could kill you too, but that's a different story.

    Might be time to run two new 12/2 circuits. Feed the first outlet with a GFCI recepticle in each branch and you'll be good to go.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #3

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    There's nothing wrong with a shared neutral (or with ring mains, for that matter), if done properly. Standard service in the US is 120/240. For a shared neutral the two hot conductors must be connected to opposite phases in the panelboard. For this reason the code requires a handle-tie between the two breakers. That way you are forced to put them side by side, which, with a standard panel board means they will be on opposite phases. This also means you can't use tandem breakers, etc.

    In theory, if you are using only one circuit the neutral carries the entire return current. However, if you are using power on both circuits, the neutral carries only the difference in the two currents, since the circuits are on phases that are 180 degrees apart. When the return current from one phase enters the neutral, it is met by a current from the other phase that is opposite in sign. The two currents cancel each other out, leaving only the difference to flow in the neutral. Thus, when using both circuits the neutral will carry little or no current. This is only true if the circuits are on opposite phases, thus the code requirement for the handle tie.

    Having said that, if you want the ultimate in protection (and want to make the electrical vendors happy) you can put in AFCI breakers on the circuit and then put in GFCI receptacles in the kitchen However, your "spare" AFCIs won't work with the shared neutral, you would have to re-wire to non-shared neutrals. Also, a "combination" AFCI refers to an AFCI that can detect both series and parallel arc faults, they do not have any features of a GFCI, so you will still need either GFCI breakers or receptacles. There are only a few two-pole shared neutral AFCIs out there, if they happen to fit your panelboard they are very expensive.

    Speaking of which, how are your receptacles wired? The non-GFCI receptacles can be protected if they are wired through the GFCI receptacle. For any string of receptacles you only need one GFCI to protect the entire string, but you have to wire the downstream receptacles to the pass-through terminals on the GFCI, rather than connecting them to the incoming circuit.

    The code does like to see the dishwasher/disposer on separate circuits (commonly a shared neutral arrangement) with the general kitchen service receptacles on entirely separate circuits, but a lot have been installed the way you describe and it doesn't present too much of a problem as long as you are not overloading the circuit.

    Lastly, from your own post a couple of threads ago, you can run the 12-3 under the joists if you put up running boards. Bottom line, I'd probably leave it as is, put up running boards to protect the wire, and check the wiring of the GFCIs to see if they are wired for passthrough to the standard receptacle.
    Last edited by DSanduril; 09-12-2009 at 10:09 PM.

  4. #4

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    Quote Originally Posted by DSanduril View Post
    ...Also, a "combination" AFCI refers to an AFCI that can detect both series and parallel arc faults, they do not have any features of a GFCI, so you will still need either GFCI breakers or receptacles...
    Just want to highlight this point. To my knowledge, there is no such thing as a "combination" AFCI/GFCI. The word "combination" refers to AFCI's only. And the combination means the AFCI protects for more things as said above.

    Perhaps the word "combination" is not the best choice of word for this and I can see where someone might think it is an AFCI and a GFCI. Not the case! And no such thing exists so far as I know. It is either an AFCI, a combination AFCI, or a GFCI.

    And with a GFCI, you can get a GFCI breaker or a GFCI outlet.

    So far as I know, you can only get AFCI breakers.

  5. #5
    Extreme DIY Homeowner Scuba_Dave's Avatar
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    NEC 2008 requires a 20a 240v breaker in order to run a MWBC
    Not required to update existing circuits
    Only GFCI required in the kitchen at present
    I'd run (2) 20a circuits & protect the 1st outlet of each circuit w/GFCI
    This all depends upon access within the walls

    What they may have done is run 12-3 to the 1st outlet(s)- GFCI, then run 12-2 after that for each sepearate circuit to maintain GFCI protection

    My fridge is on a dedicated 15a circuit w/12-2 wire (just in case)
    When we install a dishwasher it will have a dedicated circuit too
    No disposal, kitchen is on the opposite side of the house from the main drain
    Slope is not that great & crud builds up just with reg small junk washed down the drain

    All depends upon if you are remodeling
    I wouldn't tear apart walls to fix what ain't broke
    But I would dedicate a circuit for the fridge, possibly dishwasher too if easy enough to run wires
    DIY Handyman (not 4 hire)
    I have enough to do to my own house

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    Senior Robin Hood Guy Ian Gills's Avatar
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    Thanks. It's quite an easy fix actually. The kitchen circuits are individually wired in Romex, come down into my my basement and then enter a box. From the box to the panel is the shared neutral and this is the run I am replacing.

  7. #7
    Homeowner Thatguy's Avatar
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    Find the outlet farthest upstream of the kitchen outlets [there's a way to do this with a 10A load and a DVM] and put a GFCI there and label the downstream outlets as GFCI protected.
    Last edited by Thatguy; 09-13-2009 at 05:02 PM.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    A GFCI compares the current on the hot and neutral...on a shared neutral system, it may not be balanced and (I think) could give the GFCI fits. Yes, it will work fine with regular outlets...I'm not sure it will when you throw in a GFCI.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    Sound and Light Suppervisor for a School District tjbaudio's Avatar
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    I would not want an AFCI in the kitchen. The motors in mixers and similar can trip them. GFCI work better closer to the usage point. Try to keep the refrigerator off of the GFCI.
    tjbaudio
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  10. #10
    Homeowner Thatguy's Avatar
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    Quote Originally Posted by tjbaudio View Post
    I would not want an AFCI in the kitchen. The motors in mixers and similar can trip them. GFCI work better closer to the usage point. Try to keep the refrigerator off of the GFCI.
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