I know we've talked some about best practices when mounting electrical boxes in ICF. I'm having a hard time finding appropriate boxes for ICF, though. I prefer to use a 4" square box with a mud ring. I use 12 AWG throughout, and the 4" box affords plenty of room when shallower boxes are used. The only thing I can find is either metal, or plastic with attached nail brackets. I like the plastic because it has bosses intended for screws in the back, so it could be anchored to the concrete with Tap-Cons. I believe interior screws are against code for metal boxes. I want my boxes mechanically fastened in addition to foaming in. The problem is the large nail brackets. I guess I could chunk out the foam to clear them, and then re-foam once mounted. I'm sure the inspector would freak out if I sawed them off. After searching for hours, i can't find a plain box without the nails. What are you guys using?

While we're at it, do any of you use metal studs for interior walls? I went to metal because the available wood is so terrible, and metal is now cheaper than lumber! Again, it's hard to find a good electrical box for metal studs. There are a number of boxes with a flange that mounts to the front of the stud, but they're pretty thick; I'm afraid of having a hump in the drywall next to each box. Can you get boxes with a side-mount-only bracket?

We like these:

INEXO by Ipex LLC

Those are nice, if a little expensive. Can you buy them in small quantities? I see they are priced per 100. If I could buy one box (18) that works out just right for the outlets in my external walls.

Jay, if you google metal studs and electrical boxes and then look at images you will find several types that mount inside the stud or have a bracket to mount a box between the studs

David

Posted By jdebree on 03 Jun 2013 09:53 AM
I believe interior screws are against code for metal boxes.

Unless the NEC part that is in the 2006 IRC has been added to, boxes in ICF walls fall into kind of a dark hole. The pertinent requirements I find are: must be securely fastened; if fastened to a structural member, i.e. like a stud, external mounts are to be used; screws and nails can pass through the box within 1/4" of the back or sides; no screw threads may remain exposed inside the box.

I believe the bosses in plastic boxes are there to help shield  the wires from anything metallic, i.e., the screw heads, since the boxes cannot be grounded. I find no restriction against using screws inside metal boxes to fasten them to a surface. I tried using Ramset fasteners but they didn't work worth a crap to fasten boxes.

Cutting the ears off of a plastic box would modify the box from its UL approved configuration so would not be allowed, although I think I did it in a place or two where I figured the inspector wouldn't see it. It's another case where practicality clashes with "one size fits all" rules.

When you use a plastic box the wire does not have to be clamped in the box, providing it is fastened to the structure within 8" of the box. Wires foamed into grooves in ICF are pretty secure, but if you happen to encounter an anal-retentive uncooperative electrical inspector he might not buy into it. Also, make sure the wire is at least 1 1/4" behind the surface of the ICF foam its entire length.

My contractor simply glues the boxes in with foam. It's surprising how strong commercial foam is, but I worry about years down the road if the foam degrades. I hate wobbly outlets, and it's going to annoy me no end if they loosen up over time.

I'm not sure what they mean by screws passing through the box within 1/4" of the back or sides. Does that mean that the head can't protrude more than 1/4"?

I'm not too worried about inspections; so far, they've only made very brief glances at my work. They haven't been on-site for more than a few minutes for each inspection. It's important to me that everything meet or exceed code, though.