On 2005-01-23, HorneTD wrote:

Make sure that your boxes are large enough for the number of wires,
devices, and interior clamps that they will have to contain.

Yes, this is always good advice. One advantage of the fact that my
receptacle boxes are mounted in the baseboard is that I can fit a 3.5"
deep box in my 2x3 walls (1908 house). I had a heck of a time getting
a big enough double gang switch box for a light and (separate) ceiling
fan control in a 2x3 wall, since I could only use a 3" deep box. 7
conductors, EGC and 2 yokes makes 12 allowances, which is 27 in^3 for
12 gauage wires. Most shallow PVC boxes are 25 in^3, I had to track
down a fiberglass box from Allied Moulded that is 28 in^3.

Even with the 3.5" deep boxes, it seems hard to stuff the wires into a
single gang box, since it is difficult to push the EGCs all the way
into the very back, as the box is not that wide and the device is
somewhat in the way at this point. Is there any secret to this?

As an example a 3" X 2" device box that has a receptacle served by a
twelve gage, twenty ampere, circuit with the cable held by internal
clamps and Equipment Grounding Conductors in the box would need to
be three and one half inches deep to have the requisite number of
cubic inches capacity.

My understanding is that the volume stamped on a non-metallic box
already takes into account any clamps built into the box and that no
allowances are required. The clamping allowances would apply when
dealing with a metal box of standard sizes, with the internal clamps
at the back of the box, since these boxes are available with and
without internal clamps. Is this correct?

Cheers, Wayne