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Exterior Receptacle Box With Two Unbonded Plugs

Kyle Bentley | Posted in Building Code Questions on

I’ve got a single external receptacle with easy access to the wiring, and I’ve been struggling to find the code that supports what I think is OK.

To avoid cutting siding for another box, I’d like to run two 12 gauge romex to a duplex receptacle (exterior) where the two plugs are unbonded.  on the breaker end, both hots are connected to a square D QO 20A two pole breaker.

This effectively provides two reliable 15A circuits so that say, a table saw and an air compressor can run at once, and trip both if one of the plugs exceed current, while preserving space.

I’ve looked through the free access version of the 2020 NEC, but man is that web portal brutal.  Can anyone smack my hand, or provide a quick reference on where to find supporting docs?

Thanks!

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Replies

  1. Patrick OSullivan | | #1

    I'd never really considered doing this, but it seems workable, as evidenced here: https://www.ecmag.com/section/codes-standards/using-two-pole-breaker-feed-split-wired-receptacles-break-tabs

    The most important code reference is (or seems to be): "210.7 Multiple Branch Circuits. Where two or more branch circuits supply devices or equipment on the same yoke or mounting strap, a means to simultaneously disconnect the ungrounded supply conductors shall be provided at the point at which the branch circuits originate."

    So, the two pole breaker, or two single pole breakers with an approved handle tie, is necessary.

  2. Kyle Bentley | | #2

    Thanks for the link, that describes it nearly exactly. My plan was to break off both tabs making them truly independent, but I hadn't considered the case where the neutrals are bonded. Either way the simultaneous on/off of both is a requirement.

  3. Jonny_H | | #3

    The potential issue I'd see here would be the requirement for GFCI protection on exterior receptacles (210.8(A)(3))-- I've never seen a GFCI receptacle that can be split, so you'd need to use a 2-pole GFCI breaker or also run separate neutrals and use a pair of GFCI breakers.

    1. Kyle Bentley | | #6

      I'd planned on GFCI at the breaker, I just didn't list it in the post to keep it shorter. Good tip though to those who read later.

  4. DCContrarian | | #4

    This is done all the time in kitchens. Usually it's wired with 12/3 and a shared neutral. It's called a "multi wire branch circuit." If they're on the same breaker they will be out of phase and there will be 220V across them, so yeah, you need to break that tab. The two breakers need to be tied.

  5. Expert Member
    Zephyr7 | | #5

    You’re ok doing this, and you don’t need to split the neutral if you use a double pole breaker — you can share one neutral for both circuits. You would run 12/3 with ground NM cable here, with the black wire service one outlet and the red wire serving the other. There is no need to split the neutral because the two circuits are out of phase, so neutral currents cancel. This neutral sharing is ONLY allowed with a double pole breaker though.

    Note that you do have to break the tab on the hot side.

    Here’s the problem you have with the above: since this is an EXTERIOR receptacle, it’s required to have ground fault protection. You need two use a double pole GFCI breaker because of this. Those double pole GFCI breakers are a bit on the expensive side, but aside from that, your plan will work fine, and pass muster with the code too.

    Bill

    1. Kyle Bentley | | #7

      Thanks Bill,

      Good call on the GFCI breaker. I should have said something about that in the post, as others will certainly read in the future.

      I thought about a combined arc / ground fault breaker for this, any reason not to?

      1. DCContrarian | | #8

        Electric motors can trip an arc-fault.

        1. Kyle Bentley | | #10

          Googling that leads me to believe the tech has some catching up to do, or a lot of people install receptacles with the push in connections. Either way, probably just use GFCI for that one. Nice tip!

  6. Patrick OSullivan | | #9

    > This neutral sharing is ONLY allowed with a double pole breaker though.

    Double pole breakers are allowed, obviously, but a handle tie on two single pole breakers is sufficient. MWBCs need common disconnect, not common trip.

    1. Kyle Bentley | | #11

      Patrick,

      Not to split hairs down this far in the answer, but I'm mostly curious now. Two single pole breakers with connected throws would be in phase, and if the neutral (singular) wire were connected to a bonded neutral on the duplex, wouldnt this lead to a situation where two equally large loads could overload one neutral wire on the return? Now if two Romex lines with individual neutrals we're run, and the neutral tab on the receptical left intact or broken, it seems like it would be fine.

      Thoughts?

      1. Expert Member
        Zephyr7 | | #13

        Two single pole breakers mounted next to each other will be out of phase. The way the busbar in the panel is configured, every other slot on the same side of the panel are on opposite legs of the service, which each leg 180 degrees out of phase from the other. Note that this is not “two phase” service, it’s split single phase service.

        Note that a tiebar will make for a common disconnect, but not a common interruption under fault conditions. The common trip on a double pole breaker is internal to the breaker and does not require the tiebar to function. You can even remove the tiebar from a double pole breaker, and the two poles will still trip simultaneously if either side experiences a fault condition. I mention this because the OP mentioned requiring a common trip for the two circuits.

        BTW, I would avoid using an arc fault breaker here since they’re prone to false tripping. I’m not a fan of them anywhere, actually, but they are still required by code in some areas. I would also consider running 10 gauge wire if the run is very long (50+ feet or so) if you’re planning on running heavy motors on either or both of these circuits. The heavier wire will result in less volt drop under load. Be prepared for much pain buying wire with today’s crazy copper prices though! Sharing that neutral is going to save you a fair bit of money these days.

        Bill

        1. Kyle Bentley | | #14

          I didn't know they were out of phase in adjacent slots, but that makes sense now that you say it.

          I only looked yesterday as I don't buy wire often, and I though rolls were misplaced on the shelves, it's crazy town. $100 won't buy many ft of any moderate gauge wire, and I feel like I'm subsidizing someone's Christmas as Schneider, sheesh.

          Thanks for all the good info!

  7. Deleted | | #12

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  8. Deleted | | #15

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  9. Expert Member
    Akos | | #16

    I would double check your local rules, here AFCI is required on outdoor circuits. I don't think there is such thing as a two pole AFCI.

    Real pain in the @#$, the only circuit you can now plug a decent saw into is a kitchen 20A receptacle.

    1. Expert Member
      Malcolm Taylor | | #17

      It's nuts. Electricians spend months going back to new builds to trouble shoot AFCIs. Owners think it's their faulty work.

      1. Expert Member
        Zephyr7 | | #18

        It’s not uncommon to swap out AFCIs after inspection to put in regular breakers to improve reliability. AFCIs are one of those things that were worked into the code by the manufacturers and weren’t really added to address any particular real safety issue.

        The only place I or my electrical subs have seen the sort of sizzling fault that AFCIs are intended to protect against is on 277v commercial lighting circuits, where AFCIs aren’t required. I was told by another consulting engineer that there have apparently been some cases of sub-sub-sub-subletted units in large apartment complexes where extension cords have been smashed behind furniture where there have been issues.

        I’ve been told that a future code revision will change things so that AFCIs are only required in multi family properties of more than some minimum number of units, but that hasn’t happened yet.

        Bill

        1. Patrick OSullivan | | #19

          > It’s not uncommon to swap out AFCIs after inspection to put in regular breakers to improve reliability.

          It's my supposition that this is why the best place to buy AFCIs seems to be Ebay. :-)

  10. Kyle Bentley | | #20

    At this point I'm planning on skipping the afci, and just using the GFCI. It's already more than code here with what I've got planned.

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