Existing building with block wall, adding 3/4" studs and will be adding receptacles and switches

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Thomas Evans

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New Jersey
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Electrical Design Engineer
The architect is planning on furring in the outside wall. So if the back of the junction box is against the existing block wall, the face of the device plate will be 3/4" + 1/4" = 1” total. What is the minimum depth required for a J-box used for receptacles and switches? I can’t imagine that what they are proposing will work for not only the box itself but also MC cable, but they will ask me what will. I suspect Romex will not be allowed in this application, and the Romex would be at risk of damage from any gyp board penetration, before or after construction.
thanks,
tom
 
Tell them you need at least 2x3s turned the deep way, or break holes in the block.

Use Colorado Jims for the wiring.

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I would dry to get enough depth for a 2-1/8 deep 4 SQ plus mud ring so 2 a out 2-1/2 " furring or a 2x3 like Tom said would be nice. Could get by with a 1.5" box plus mudring so about 1.75 if they want every inch. DON'T let them use 2x4s in the flat it's not deep enough and the mudring will push out the drywall.
 
electrofelon said:
DON'T let them use 2x4s in the flat it's not deep enough and the mudring will push out the drywall.
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The section I quoted would allow, for circuits up to #10 AWG, a 1-1/4" deep box and a mudring. As long as the devices project into the box no more than 1". But box fill and makeup could be challenging.

Cheers, Wayne
 
I had one general that built with cinder block exterior walls and 1x furring strips. We would use a grinder to carve out 1/4" or so of the cinder block behind the boxes to make them fit. Used sheathing and drive pins to secure the romex. Inspectors bought that.
 
Is the block wall hollow, or did they fill it in?

If it is hollow maybe you can get dispensation from the structural engineer to cut out some holes in the block and insert the back of the box into the block.
 
It is super ugly, but using a Wiremold extension/adapter ring would allow enough depth to mount the devices.
I had to do this to accomodate a ceiling light switch next to a doorway with double pocket doors.
 
I would be giving customer 2 options. Frame out with deeper depth, or use of metalic wire method such as Wiremold or surface conduit. If appearnce is critical (to customer) only option probably deeper wall framing. Otherwise Wiremold would be (appearance wise) less objectionable than purely industrial look of conduit.
Really got no choice, with only 3/4 inch depth to even use in wall conduit and make connection to box even using the minimum ci fill restriction, can't be done. The offset and connectors even on 1/2 inch conduit would be more that your wall depth.
 
If you use some kind of surface mounting wiring method like EMT or wire mold, you could do a pretty good job of hiding it by painting it afterwards to match the wall. It's not perfect but it's surprising how a good paint job can hide all kinds of things.
 
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