Can I put two duplex receptacles in a 4 inch box (depth is 2 1/8") without overfilling it? I will use #12 AWG with each receptacle on its own circuit (MWBC).
Wondering if I need to upgrade to a 4 11/16 box.
Electrical – How Many Outlets in a 4 Inch Box
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Related Solutions
You might be able to get away with mounting an extension to the existing box, then using a box cover with conduit knockout and a cable clamp you could run your cable out the front of the box instead of through the side knockouts.
This keeps coming up: The question of whether you can put more than one receptacle on a 30A circuit.
All the receptacles must be 30A. (NEC 210.2B3)
It's very surprising to find 30A plugs on machines that fall considerably short of 30A. Generally they use a 15A or 20A plug if they are able.
I'm not sure you can fit two of those connectors two abreast in a 2-gang box. That's a mighty tight fit, and I'm concerned with the screws striking each other.
It'll be tight and awkward to grab, and depending on the plug, they might interfere. I'd go a double-gang bolted to a single-gang with a conduit nipple.
Big receptacles don't have 2 screws, so you'll need to pigtail them. The extra wire count will mean you'll have a lot of box fill, in both the Code requirements and in the actual sense. You'll need a very deep box.
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Best Answer
Raised exposed work cover, or flush cover?
4 x 4 x 2-1/8 is 30.3 cubic inches. That fits 13 "counts" of 12 Gauge at 2.25 cubic inches per count. If using a raised cover they typically add 6.5 cubic inches or so.
What is a count? A wire terminating in the box, a wire passing though the box, 2 counts per yoke device (ie, a receptacle) 1 count for all grounds (unless using NEC 2020 where additional ground wires [edit: beyond 4] count as 1/4 of a wire...) Edit: right, I don't use NM/B, and if I do I use clamps that are external to the box. If you use clamps internal to the box they add 1 to the count.
If the outlets are on one circuit, you presumably have 3 wires in (hot neutral ground) 2 wires out, and 4 "wires" for the two yoke devices.
9 * 2.25 = 20.25 which is less than 30.3 so you are good. (even with clamps in the box)
If the two receptacles are on different circuits, 5 wires in, 4 wires out, 4 for devices. 29.25 inches which is less than 30.3 so you are good.
Edit: Ah, you said MWBC, so subtract a wire each way (one neutral in and out, not two) still good. And remember to pigtail your neutrals.
Pigtails (wires that do not leave the box) are, incidentally "free" (they don't add to wire count.)
Wires that pass though without connecting to anything in the box count 1 unless they are 12" or longer, in which case they count 2. This effectively differentiates between "just passing through" and "leaving enough to a possible future connection" since you are supposed to have 6" for a connection.
As with conduit fill, not being right up against maximum box fill is more comfortable to work in.