I would like to know if you can have more then 2 circuits in duplex box, for example splitting 2 duplex outlets into 4 individual circuits. Treadmills are all residential and require dedicated 20amp 110v circuits, just trying to avoid so many boxes as there going to be in a more open area. Thanks in advance for help

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    The point is, this site is for DIY home-improvement only. Commercial work is off-topic (and generally illegal to DIY).
    – nobody
    Nov 25 '21 at 2:39
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    @statueuphemism I don't know about treadmills, but I do know people who get together in real life, at someone's house, to ride their turbo trainers. A big active family could easily want to run together, just indoors in winter
    – Chris H
    Nov 25 '21 at 13:05
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    @JPW Please clarify: Is this a personal, private residence or is this a commercial location or shared (e.g., condo building gym shared by all residents)? The technical aspects don't change (generally) but it determines whether you can do the work yourself vs. need to hire a licensed professional. Nov 25 '21 at 15:42
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    @manassehkatz Comment on an answer: “Yes residential grade treadmills for a friend starting a home gym out of his home.” This was the intent of my original question was to get this sort of clarification. Though, in hindsight it could have been phrased better. The official answer on this one is that the arrangement is legally sketchy all around and I would personally stay far away from it, but the technical aspects are certainly doable and are done all the time for other reasons as you already noted. Nov 26 '21 at 16:04
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    Could you re-state this question with information that will help focus the answers on the problem you're trying to solve? Are you using conduit or NM or armored cable? Do you want to bring FOUR 12/2 cables into one two-gang box ? Can you explain why, in a room with four treadmills and four power cords it would be so bad to have a four-gang box or two, two-gang boxes positioned so none of the power cords has to cross any other treadmill? That is what I would want, an outlet between each pair of machines and no cables running all around the floor.
    – jay613
    Nov 26 '21 at 19:12

Update based on a comment: residential grade treadmills for a friend starting a home gym out of his home. The specs say They also require there own individual neutrals not tied together

First of all "home gym out of his home" sounds like "commercial gym but in a house rather than a typical commercial building". I'm not worried about zoning - many places allow such small businesses in a home, even in a purely residential area, often subject only to traffic limitations (e.g., only 'n' business-related visitor vehicles at a time). However, in many locations commercial electrical work is subject to more limitations than residential electrical work. In particular, where many places allow homeowners to do limited (the limits vary dramatically by jurisdiction) electrical work on a home that they own and live in, the exception generally doesn't extend to a commercial location. This is particularly an issue because of insurance. For example, if a customer is injured, even if the injury is not electrical in nature, the insurance company may investigate and any unlicensed electrical work could be a real issue.

That also technically rules out MWBC. Actually, the rule doesn't make much sense. If you have two treadmills running at the same time then the neutral carries only the difference in current, and a double-breaker GFCI (as opposed to a handle-tied pair) will have the neutrals together at the breaker (or else the GFCI won't work). Makes no sense, unless they intend to have a separate GFCI for each treadmill, but that would require 4 gangs instead of 2.

There are two issues:

  • Wire

If MWBC is out of the running ("no shared neutral"), then this is 4 x 12/2 cables. Alternatively, it could be conduit with individual wires. The advantage of conduit (i.e., when not required for other reasons) is that while you have some up-front cost, the wires themselves often cost less than cable and that cost savings increases with multiple circuits.

In this case, that would be 4 black/red/blue/yellow/etc. (anything but white, gray or green), 4 white/gray and either one green ground or no grounds if you use metal conduit all the way from panel to metal box. However, there is a complication, derating. If you have more than 3 circuits (and here you have 4, unless it turns out you can use MWBC), you have to derate. As I understand it, you end up with a 70% derate. The problem is that 12 AWG wire starts at 25 A for 75 C and only goes to 30 A if you have 90 C terminations. I think normal 20A receptacles are not rated for 90 C, but I have not been able to quickly find an answer to that. But assuming that's the case, your derated capacity is down to 25 x 0.7 = 17.5 A, which is no longer a 20 A circuit. Which means either going to two conduits (one for each pair of circuits) or 10 AWG wire, and doing either of those will likely eliminate any savings from conduit over cable.

  • A single yoke on two circuits must be handle-tied.

Each duplex receptacle must have the tabs removed (both sides, because no shared neutral) and the circuits powering top & bottom must be from adjacent, handle-tied breakers. Can't use a double-breaker (which is the usual thing as an alternative to handle ties) because a double GFCI breaker (and you will almost certainly need GFCI here, and you can't put GFCI at the receptacle because GFCI duplex receptacles can't use two circuits) has, by definition, a shared neutral.

In addition to the possible legal issues, I'd recommend a serious look at the actual instructions for the treadmills. An overall "no shared neutral" statement really limits your options here, and I think for no good reason.

There is one more option, which would look a bit strange but is legitimate. Instead of using GFCI breakers and a pair of standard duplex receptacles, you could use 4 GFCI/receptacles in a 4-gang box. Then the breakers (unless AFCI is required) are standard breakers and the wiring is straightforward. However, you then run into the risk that someone will see the duplex receptacles and plug in another 4 large devices and overload the "dedicated" circuits.

  • Also there is a box fill limit. Worst case 8 @ #12 conductors, ground, two yoke devices, 29.25 in³. Nov 25 '21 at 3:06
  • @NoSparksPlease But that's easy: 4" steel box 30.3" Nov 25 '21 at 3:10
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    Also, for posterity for an actual residential wiring problem that lands here: While I would hope an appliance that requires a dedicated 20A circuit comes with a NEMA 6-20 plug with the sideways prong (which would make my next statement obvious), if someone goes the dedicated single 20A outlet route, then he/she will need to make sure each receptacle is 20A (NEMA 6-20) as opposed to the standard 15A receptacles. Nov 27 '21 at 22:22

Yes, however if you have a duplex outlet with two circuits, the breakers for them need to be handle-tied.

  • Yes residential grade treadmills for a friend starting a home gym out of his home. The specs say They also require there own individual neutrals not tied together so would definitely need to be double pole breakers or handle tied from what your saying so 2 duplexes 4 circuits all tabs removed 4-12/2
    – JPW
    Nov 26 '21 at 0:05

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