1 gang box fill capacity/size for receptacal and two 12/2 Romex & pigtales

Question

I am installing a receptacle in a confined space inside some custom cabinetry, so I need to use the smallest (with respect to depth) box I can that still meets code. This is a remodel so the wire itself is already in place. The box will have two 12/2 romex, one line, one load, plus 3 pigtails to the device (ground, common & hot). Pretty much the standard setup that I've seen in most receptacle boxes.

I've been trying to puzzle out the minimum box volume that I can use by reading the NEC, etc. But I don't see any indications of if I need to take the pigtails into consideration.

My preference is to use a pvc old work box because the install is into a cutout in 3/4" hardwood panel. There are no studs or such that suite for a typical new work box install. The largest 1-gang old-work box that I seem to be able to find locally is 23 cu.in. It fits my space but seems small for that much wire.

I did find this question: Box Fill Calculations Help Please - Two Romex 12-2-2

If I follow the math therein, I have 4 wires + 1 ground + 2 wire/equiv for the device = 7 wires x 2.25 cu. in. per wire for 12ga = 15.75 cu. in. That seems really tight. So is this right?

Answer 1

Any box at minimum size for wire fill IS really tight. Normally we choose to avoid it, but if you need to go there for practical reasons other than easy installation, you appear to have the math correct, assuming your PVC box is the typical sort with no internal clamps to account for.

Pigtails that don't leave the box are explicitly not counted in wire fill calculations. Only wires that pass through or terminate in the box count.

Mind, you don't actually have a need for pigtails, so you can simply connect the incoming wire to one set of terminals on the receptacle and the outgoing wire to the other set of terminals on the receptacle. But that does not change the required space for box fill at all.

Please stop referring to neutral as common. It's not.

For the smallest "with respect to depth" boxes, look away from single-gang as a box format; instead, look to a 4x4x1.5 with an appropriate cover plate to mount your device yoke to.