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
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:
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.