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Is it safe to have two power sources (meaning 2 sets of 12/2 wire) on one receptacle?

One set of wires goes to breaker #2 and another set of wires goes to breaker #7 but both 12/2 wire sets were hooked up into one receptacle.

Just curious why someone would do that.

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    Are the receptacle's "tabs" broken off? Nov 12, 2020 at 0:34
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    One very common place to see this is on a kitchen under-sink outlet -- one half of it for the dishwasher, and the other half for the garbage disposal. Since dishwashers sometimes need a dedicated circuit for themselves, wiring it in this way makes it easy for the homeowner to use whatever devices there that they want.
    – Nate S.
    Nov 12, 2020 at 0:49
  • No broken tabs, thanks for the help! Nov 12, 2020 at 0:57
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    @SMLFoundation, If the tabs "links" aren't broken off, then this wouldn't really be 2 separate circuits, and would represent a bad situation.
    – Glen Yates
    Nov 12, 2020 at 17:00
  • Can you Post a diagram and either way, what did your text-books leave unclear, please? Nov 13, 2020 at 2:53

3 Answers 3

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Sounds like they messed up and accidentally made a "ring circuit".

It's possible to have 2 circuits legally on one receptacle (the 2 sockets and frame called a "yoke"). However, if you do have 2 circuits on a yoke, the breakers MUST be handle-tied with a factory provided handle-tie.

Otherwise a maintainer could plug in a radio and shut off circuits until the radio goes silent, then pull it out and get nailed by the other circuit.

A 2-pole breaker (that's a 2-pole NOT a duplex/twin/tandem) will also satisfy the requirement since its handles are tied. They're a lot easier to obtain than handle ties.

Generally, handle-tying implies that they will be on opposite poles of 240V service (i.e. 240V between the different hots). This is one of the very few cases where a handle-tie on a tandem would be alright, but they don't make any such thing, not least because it would be bad in any other application.

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  • I follow you and agree. However, how would this work as a "ring circuit"? There would be 120v flowing out of the hot on both circuits, would it "automatically" balance itself to return 120v on the neutrals flowing back? Would there be varying amounts of current flowing back? Maybe I should ask a new question over at Electrical Engineering...
    – FreeMan
    Nov 12, 2020 at 14:07
  • If space isn't a premium, would it be better to simply use two single outlets? Otherwise, if someone replaces the outlet without breaking the neutral tab, and one of the neutral wires fails, the other neutral wire could be stuck carrying twice its rated current without any indication of problems until things overheat.
    – supercat
    Nov 12, 2020 at 16:43
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    @FreeMan Voltage doesn't flow - current flows. It's a ring circuit because you've got two hots breakered at their respective sources that join up at the device. This means that either the top or the bottom recep could pull up to 30A before tripping since the current will balance (roughly) between both feeds (ie: a 15A load would pull about 7.5A from one hot feed and about the same from the other). This is how british circuits are generally configured because it allows twice the current for the same size of wire (saving copper was important after the war).
    – J...
    Nov 12, 2020 at 18:23
  • @FreeMan Actually, the British way is more dangerous because (afaik) two wires leave the same breaker and the breaker expects that both wires will share the current. If the ring suffers a break then you can easily run way too much current through the wire (which is why this isn't allowed anywhere else). In OP's situation, though, each wire itself is breakered at 15A, so a break in the ring won't lead to overcurrent on either branch. It's still not allowed, in any case.
    – J...
    Nov 12, 2020 at 18:24
  • @Yes, that compound failure (replacing without breaking tabs; failed neutral) would cause that, indeed. However if they are following the "approved handle-tie" rules, the hots will almost surely be on opposite poles, so the non-tab-breaking replacer person will be notified of the wiring error. Yes, I agree that if space is no object, 2 receps in a 2-gang box are better than a split recep - not least, a non-split recep can be replaced with a GFCI recep! Nov 12, 2020 at 18:28
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The only time this is safe is the receptacle is a dual receptacle with the tabs removed. Then it is actually 2 separate receptacles with separate power sources. Even then, it is not a good idea unless it is a Multiwire Branch Circuit (MWBC). With an MWBC, the breakers are next to each other and connected so that if you turn off one, the other is turned off as well. An MWBC has another advantage in that you get a "free wire" by using one neutral wire instead of two.

However, with breakers 2 & 7, they are not next to each other in the panel and there is a real problem (don't know if this is code or not, but common sense in any case) that if you turn off one breaker, turning off the top receptacle, the bottom receptacle - with live wires - is still on.

On the other hand, if the breakers are connected to the same receptacle - i.e., either exactly the same or one to top and one to bottom but the tabs were not removed - then this is a very dangerous situation, for a bunch of different reasons.

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    Well, you are correct that the breakers need to be handle-tied when feeding the same yoke, but it's technically not a MWBC at that point due to the lack of a shared neutral Nov 12, 2020 at 0:44
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    It is code today that two circuits supplying the same yolk must be handle tied. I'm not sure when that was added so it's plausible that OP's installation was grandfathered.
    – Nate S.
    Nov 12, 2020 at 0:55
  • "supplying the same yolk"... in the chicken coop? :-) Nov 12, 2020 at 16:07
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Large power use expected, perhaps. If the tabs on both sides of the outlet were broken, it's not exactly wrong. If they were not, it's exactly wrong.

However, they should be adjacent breakers and should be handle tied, to prevent turning off the breaker you found when checking one side of the receptacle and failing to turn off the other breaker as well (this may have happened to you, I suspect.) At which point they COULD have been done as an MWBC on three wires (+ground), but doing them as 4 wires (+grounds) is fine so long as both tabs are broken.

Then again, you could cap off and tag one cable and just have one breaker feeding the receptacle (a new one if the tabs were broken off)

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