Welder Receptacle - What Electrical Box

SNAFU

I am installing a 30A 240V receptacle for a welder in my attached garage. I have installed 10/2 Romex wire and purchased a NEMA 6-30R receptacle and device cover plate that has 4 screws in it.

My question is what electrical box do I need to install? The flush mount receptacle is 1.5 inches deep. I am in Canada and calculated box fill to be:

Conductors (2x2.25) = 4.5 cu.in
Receptacle (1.5 in x 5 cu.in/in of depth) = 7.5 cu.in
Ground (N/A) = 0 cu.in
TOTAL = 12 cu.in

I originally wanted to install a 4x4 box with a single device cover. The receptacle fits into this device cover fine, but the cover plate doesn't seem to fit properely. The 4x4 single devide cover interferes with the 4 cover plate screws that attach the cover plate to the receptacle.

The other alternative I thought of was to use a surface mount utility box (4"x2-3/8"x1-7/8" deep) and flush mount it. This box has a volume of 16.5 cu.in. The receptacle fits in fine and the 4x4 cover plate screws on fine too. Is there any reason I can't, or shouldn't, use this box?

What are my options?

Thanks

a7ecorsair

I just picked up a plastic "high voltage" box that has screw spacing to work with dryer four wire receptacles. Not sure what is available where you live.

SNAFU

Thanks. What size is the box?

Speedy Petey

I use a deep 2-gang nail on device box for this. The receptacle has four holes that line up with the four device holes in the box.

SNAFU

Yes it does!

I never thought of this, but I put two single gang boxes together as a test and this will work perfect. Thank you very much. I was loosing sleep over this. Now its off to Home Depot to get the correct box.