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Can fixtures in a single box be powered from 2 different circuits? I' planning on installing a 5-gang box with 3 light switches and 2 receptacles.

The lights and receptacles would be on different circuits. Further, the lights will be on a 15amp non-afci circuit, using 14-2 cable and the receptacles will be on a 20am afci circuit using 12-2 wire.

I plan on keeping the neutral and grounds (and obviously hots) for the 2 different circuits in the box separate.

Is there anything that would not permit this in the code (I couldn't find anything)?

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  • What size box are you planning to use for this? Jan 23 at 19:21
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    Given the difficulties of sourcing 5-gang boxes and covers for same (in the various combinations you might require)... you would be better off having 2 boxes. This would then give you the opportunity to separate the circuits. Jan 23 at 21:04
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    Using gangable boxes, I've made a 5-gang box. It is 3" deep. For aesthetics, I'd prefer to keep it all in a 5-gang box and not 2 separate boxes, if possible. Jan 24 at 1:17
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    I would tie all the grounds together. It is not prohibited, and I am curious if anyone knows if it is recommended in this case (assuming nothing wierd is going on like recepticles with isolated grounds). Keep your neutrals separate in any case.
    – bigchief
    Jan 24 at 2:30
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    @ThreePhaseEel The box will house : 2 4-way dimmers, 1 single pole dimmer and 2 duplex receptacles. As such, coming into the box are: 2 14-3 cables (for the aforementioned 2 lights on a 4-way), 2 14-2 cable (power source and single pole light) and 1 12-2 cable for the 2 duplex receptacles. Going out of the box are 2 14-3 cables to to other remote box in the 4-way setup, 1 14-2 cable (power source) and 1 12-2 Jan 24 at 13:28
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Yes, you can -- just mind the box fill and labeling, and make sure to keep your neutrals separated!

A five gang box composed from gangable, 2¾" deep boxes as you describe provides 70in³ of fill (14in³/gang as per the Steel City catalog). You are bringing 4 14/3, 3 14/2, and 2 12/2 cables into the box, in addition to mounting five devices in it, three of which are connected to 14AWG wire and the other two connected to 12AWG wire.

This means that we are using 72¾in³ of fill; 36in³ for the 18 14AWG wires, 9in³ for the 4 12AWG wires, another 9in³ for the two receptacles, 12in³ for the lighting controls, and finally 6¾in³ for equipment grounding, as per the 2020 NEC rule that requires an extra equipment grounding allowance for every four additional ground wires past the initial allowance's worth. This is just a hair over what your box supplies, and would be legal under the 2017 NEC fill rules as the fill for the additional grounding wires is what pushes it over the top, but doesn't account for any cableclamps internal to the box. As a result, I would go with a 3½" deep box if you are sticking with the field-gangable boxes, or order in a factory-fabricated 5 gang box that is taller and thus provides more fill volume if you'd rather go that route.

You'll also want a consistent way of labeling your wires so that you can tell the various circuits involved here apart; crossing your streams could lead to false AFCI trips, overloaded neutrals, and other such badness. Thankfully, premade wire labeling booklets are available for this job, and make this relatively simple; all you have to do is come up with a consistent scheme for using them.

Finally, even if you don't use the wire labels, you must keep your neutrals on the two circuits separate for the reasons mentioned above. However, you also must join all the equipment grounding wires involved together and pigtail them off to the box and to the receptacles (unless they are self-grounding that is). (Think of how this'd turn out if you were wiring this in Chicago, where you'd have to use metal conduit instead of cables.) In fact, you could use a divider in your box between the three lighting controls and the two receptacle devices; you'd then need grounding pigtails in both compartments, but it would make it much easier to keep your circuits apart.

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Yes, you could combine two circuits in a 5-gang box, but why? Not why "2 circuits", why "5 gang"?

You can easily put 3 light switches, provided they are on one circuit as you described, on one switch like this one: Leviton triple switch

As far as "2 receptacles", I'm not sure what you mean. A standard duplex receptacle is one gang. You can certainly have two of those (or a quad) in a 2-gang box, which would get you to a total of 3 gangs.

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    Neat, haven't seen something like this before. Unfortunately, it isn't an option for me. I need dimmers and also, the line of fixtures I'm using through out the house doesn't carry this. Also, I mean 2 duplex receptacles. \. Jan 24 at 1:19
  • Yes, dimmers make a difference. In future questions you should mention if there are dimmers, smart switches, timers, etc. involved as those kinds of things affect answers in various, sometimes unexpected, ways. In my (limited) experience, using dimmers is more dining/living area, receptacles next to switches is more kitchen/bathroom/workshop, so having 2 duplex receptacles next to 3 switches is unusual (though not impossible or against code). Jan 24 at 1:23

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