boxes in ICF walls and 314.43

[rszimm]

Putting in electrical in ICF walls. This particular manufacturer has 2-5/8" of foam over the concrete core. The typical way of installing boxes in ICF is to use a bracket type plastic box secured to the plastic web (like a Carlton B118B-UPC), however, I've been advised that the plastic web isn't as strong as a wood stud, so mounting it like that tends to leave you with a box that isn't as secure as you might like.

So, my backup plan is to use a B118A (no mounting bracket, but exactly the right depth), but pop two tapcons through the back into the concrete. That'll hold like crazy, but now I think I'm running into NEC 314.43.

Is putting tapcons through the back of the box acceptable? If I dab a little liquid tape over them, does it make it acceptable?

An alternative is the SN236-V which appears to have dedicated holes in the back for mounting. I'm assuming these would be OK..??

The final alternative would be a steel box with a shim in the back to make it the right depth. That's not my ideal as the steel is more expensive, more time consuming to install, and not as deep as the plastic (thus less valuable cubic-inches).

 

[infinity]

1) So, my backup plan is to use a B118A (no mounting bracket, but exactly the right depth), but pop two tapcons through the back into the concrete. That'll hold like crazy, but now I think I'm running into NEC 314.43.
Is putting tapcons through the back of the box acceptable? If I dab a little liquid tape over them, does it make it acceptable?

2) An alternative is the SN236-V which appears to have dedicated holes in the back for mounting. I'm assuming these would be OK..??

3) The final alternative would be a steel box with a shim in the back to make it the right depth. That's not my ideal as the steel is more expensive, more time consuming to install, and not as deep as the plastic (thus less valuable cubic-inches).

Two with dedicated holes that shield the screws or three would be acceptable. IMO liquid tape isn't going to cut it unless you can get prior approval from the AHJ.

314.43 Nonmetallic Boxes. Provisions for supports or other mounting means for nonmetallic boxes shall be outside of the
box, or the box shall be constructed so as to prevent contact between the conductors in the box and the supporting screws.

 

[rszimm]

Thanks. That's what I figured. I see people putting drywall screws through the side of plastic boxes every day and no one ever says anything, but that's clearly a violation of 314.43.

I'll probably do the SN236-V for all the double-gang boxes and use steel for the single gang. I can't seem to find a single gang plastic box with the dedicated mounting holes in the back...

 

[Little Bill]

Two with dedicated holes that shield the screws or three would be acceptable. IMO liquid tape isn't going to cut it unless you can get prior approval from the AHJ.

One of the stupidest rules that I know of. You can mount a metal box that way but not a plastic.
@rszimm could you use a 4" sq box and use mud rings?

 

[kwired]

One of the stupidest rules that I know of. You can mount a metal box that way but not a plastic.
@rszimm could you use a 4" sq box and use mud rings?

That is what I have almost always used.

Unless it is all ICF house you typically only have a limited number of boxes in the basement and it won't break the budget if you hadn't accounted for them upfront.

 

[infinity]

For me a metal box with an adjustable mud ring so no shimming necessary.

 

[Little Bill]

For me a metal box with an adjustable mud ring so no shimming necessary.

What is an adjustable mud ring, don't recall seeing one?

 

[infinity]

We've been using these a lot lately where you have a combination of 2 hour fire rated (2 layers of 5/8 Sheetrock) and one hour rated walls (single layer).

 

[kwired]

We've been using these a lot lately where you have a combination of 2 hour fire rated (2 layers of 5/8 Sheetrock) and one hour rated walls (single layer).

Are they less cost than a 1.25" mud ring?

Does the adjustment screw interfere with GFCI's, Dimmers, or other large body devices?

 

[Little Bill]

Cool!
I'm sure my SH doesn't carry them but probably could if needed. Those would come in handy for some of the "shotty" drywallers around. I usually go with a 1/8" larger mud ring than the drywall being used. Such as: for 1/2" drywall I use a 5/8" mud ring. But sometimes the drywallers do something to screw that up. With these adj rings, that would solve that!

 

[kwired]

Cool!
I'm sure my SH doesn't carry them but probably could if needed. Those would come in handy for some of the "shotty" drywallers around. I usually go with a 1/8" larger mud ring than the drywall being used. Such as: for 1/2" drywall I use a 5/8" mud ring. But sometimes the drywallers do something to screw that up. With these adj rings, that would solve that!

Sure it isn't framer's that did something wrong, or warped lumber causing issues?

Drywall doesn't typically change thickness after it is hung, finishers can build up a corner, seam, or other repair with a fair amount of mud sometimes though

 

[texie]

There are boxes available made for ICF.

 

[rszimm]

Ive seen the boxes made for ICF advertised. I'm not sure I trust them. They've got big hooks that extend out into the foam that supposedly keep them in place. That's probably a lot better than screwing into a web, but I just feel more comfortable with a box mounted directly to something solid (like concrete or wood).

Honestly I think I'll just go with the 4" box and rings. This is a shop/basement and plastic boxes, even if they're tapconned to concrete, are probably a bit flimsy for those 50A and 30A receptacles...

 

[kwired]

Ive seen the boxes made for ICF advertised. I'm not sure I trust them. They've got big hooks that extend out into the foam that supposedly keep them in place. That's probably a lot better than screwing into a web, but I just feel more comfortable with a box mounted directly to something solid (like concrete or wood).

Honestly I think I'll just go with the 4" box and rings. This is a shop/basement and plastic boxes, even if they're tapconned to concrete, are probably a bit flimsy for those 50A and 30A receptacles...

I never seen one, but if they are anything like a 4 inch square with mud ring that has smaller opening than the main body of box, it will be sandwiched behind the drywall and won't really go anywhere after drywall is installed, so it just needs to remain secure enough until drywall is installed.

 

[Little Bill]

Sure it isn't framer's that did something wrong, or warped lumber causing issues?

Drywall doesn't typically change thickness after it is hung, finishers can build up a corner, seam, or other repair with a fair amount of mud sometimes though

I'm sure sometimes it's the framers or the wood. But I find a lot of drywall mistakes whether it's the hangers or finishers. The adj box would help in some of those cases.

 

[rszimm]

Here's what the ICF boxes look like: https://www.wind-lock.com/icf-elect...ox-w--icf2rl?returnurl=/icf-electrical-boxes/

 

[hbiss]

From that cut sheet:

... and work with NMD Cable 14/2 - 10/3.

What the heck is NMD?

-Hal

 

[rszimm]

Don't tell me you're still using NM-B? That was two whole revisions ago!

 

[curt swartz]

From that cut sheet:

... and work with NMD Cable 14/2 - 10/3.

What the heck is NMD?

-Hal

Think Canada........

 

[infinity]

Are they less cost than a 1.25" mud ring?

Does the adjustment screw interfere with GFCI's, Dimmers, or other large body devices?

Not sure about the cost (I would assume more) but yes GFCI's and large devices do fit. We use these in apartment house construction with those devices.