box fill

[Innovate1]

Looking at box fill for wiring. Here minimum size wire is #12.

18 cu in box (cheapest plastic one I think) allows 8 conductors - that's 2 for the device (switch or receptacle), 1 for ground leaving 5, which allows 2 conductors in and 2 out.

20 cu in box allows 8.9 so no more allowed - just more working space to make things a bit easier.

22 in box allows 9.8 conductors - but has integral clamps which count as 1 so still not allowed to have more runs.

So it appears to get more than an input and output cable (and I want neutral in all boxes) I need to go to a 2 gang box with single extension ring.

Dual box is 32 cu in - this allows 14 conductors. Take away 2 for the device, 1 for ground, and one for clamps and that leaves 10. Enough for 5 two conductor NM cables.

For a dual box with two devices I could have 4 cables. And the volume of the extension ring might allow more.

Am I right on this? Thinking I should use 20 cu in as my minimum size and probably need several dual with single rings and some dual with dual rings...

 

[u2slow]

I always go larger than needed.

For me, there's always a chance of an extra cable, or a larger than anticipated device. I use a lot of 4x4" deep boxes with device/mud rings. Sometimes I'll use two boxes in close proximity.

 

[Bert_]

If it's getting wired with Romex I use common 22.5 cu in carlon boxes, no clamps. You can run 3 #12 wires into it. No reason to need more. The boxes are cheap. Don't make it to complicated.

 

[Jim greengo]

I like the allied 1098 boxes .
My go to for single gang.

 

[Innovate1]

If it's getting wired with Romex I use common 22.5 cu in carlon boxes, no clamps. You can run 3 #12 wires into it. No reason to need more. The boxes are cheap. Don't make it to complicated.

I found cheap 18 and 20 cu in boxes with no clamps but the 22 have clamps. Just a part of the plastic mold that springs to clamp the wire. But I see now the 22.5 size boxes without clamps - need to get a few of those. And take back my 18 cu in boxes. No sense fighting with small boxes.

 

[sparky 1971]

I use the cheap blue Carlon 22's. I used to use the Carlon Super Blue's but they have a "step" inside them that makes it a pain to shove the wires all the way to the back.

 

[Innovate1]

I use the cheap blue Carlon 22's. I used to use the Carlon Super Blue's but they have a "step" inside them that makes it a pain to shove the wires all the way to the back.

I think the 22s I have are the super blues - they have the step. Will return them for the square ones.

 

[Terry D]

I use the blue 22.5 for all my device boxes. I don't even bother with the 18 or 20. If I need more room I will use a plastic 4x4 with a mud ring. I like a lot of extra room in my boxes for GFCI's and dimmers. I hate trying to push against wires to get the device to go in. Plus box fill calculations doesn't include wire nuts. When they refer to internal clamps, they are not referring to the ones in plastic boxes. They are referring to the ones in metal romex boxes that have the screw inside