i am remodeling a basement room, and drywalling over 2x2 furring strips, will be adding a few new outlets on this wall running 12/2 wire, standard size switch boxes are too deep with the 2x2 , would using a shallow depth 4x4 junction box (14 cubic inches) with a conversion cover on top to 2x3 size be acceptable (cover adds 3 cubic inches to box volume) for 2 12/2 wires per box? thanks

 

I believe you are asking if a plastic box with 17 cubic inches is enough for two 12/2 wires and one receptacle or switch. The answer is yes. You need 15.75 cubic inches.

 

John Wer, the key to figuring out box capactities is by knowing your available cubic inch capac. and wire size (both of which you know) #12 wire needs 2.25 cubic inches for each of the following:1) device (allow 2.25cu. inches*2=4.5) 2)all the grounds together also count as 2.25 cu inches 3)if it is a metal box with the clamp on the inside-as most are- allow again 2.25 cu. in. 4)EACH coductor that originates outside the box and terminates or is spliced in the box counts as 2.25 cu in. 5) a conductor that passes through the box without splicing --usually found in the emt. and thhn wire method- counts as 2.25 cu in ea.
Add up all of those for each box and find out if you are 17 cu in or less. Make sure to plan this out ahead of time on paper so you dont have 1 or 2 boxes with a BUNCH (<---- fancy electrical term) of splices and feed throughs.This is just the example of the math John Nelson used to arrive at his answer. This formula also works with #14 wire EXCEPT replace all mentions of 2.25 cu in with 2.00 cu. in

 

Johm Nelson, I was understanding the post to read that John was using a one gang mudring on a box (therefore it probaly is a metal box) if this is the case he also needs to add an additional 2.25 cu in if there is an internal clamp-which there usually is. This would put him at 18 cu. in.

 

Jorren, I agree with you if he's using a metal box with internal cable clamps. That's why I optimistically put that word "plastic" in my post.

 

thanks for the replies, actually i was planning on using a plastic box with a one gang mudring(which is made of plastic as well , i was calling this a conversion ring to 2x3 in my original post-see i have learned something already!) . it should have enough volume by my calculations. the main question is whether a junction box with mudring is acceptable as a normal switch box is too deep for the 2x2, i guess it is right? thanks john

 

John Wer, I'm glad to see plastic (non-mettalic) 4x4 boxes with plastic mudrings available in the "BIG BOX" stores! I'm trying to decipher your questions on the last post so here it goes....
1)That arrangement of box/mudring is acceptable to use to put a switch in. 2)using plastic, you have enough cu. in room. 3) whether it will fit is up to how good you can measure. Happy wiring!!!

 

Plastic boxes that are bigger than a single gang device box requires a form of cable clamp. If that cable clamp is formed with the plastic box and takes up more than 1/2" room inside that box then you must count a current carrying conductor count for those clamps.

The exemption of clamping for nonmetallic boxes are limited to single gang device boxes only.

Just a thought

Wg