Maybe someone else has seen this. Buddy calls me up and says he just encountered a crew mounting boxes and securing NM cable at an apartment complex job with that spray/expand foam you get at the home center for filling cracks. Did the whole job that way. They were incredulous (followed by belligerant) that he wouldn't accept it. I put together a list of Code sections but has anyone got any suggestions?
I haven't wired one, but I have asked about it, and it is pretty much my understanding that that is exactly how the cables are secured in those new concrete and foam panel houses. And they have been passing inspections all over the place. But where is a code that allows this method? Or better yet, where is the code that does not allow it?
I'm still sceptical, but in concrete, this sounds plausable. I hadn't thought of that. However, I've always piped (PVC) when working in block or concrete.
Is there a specific product designed as an adhesive? Also, the product would have to be inert (completely) or you would risk reaction with the NM jacket.
My other concern would be replacement, say, if someone drilled through some NM in the wall. Now that the cell is full of foam, the cap would have to be removed and the foam dug out, etc. If the cap is inaccessable, we're now busting out concrete or block...not good planning.
I still can't see myself using this method. It just doesn't seem right.
I must confess to having used foam ONCE to secure an existing box. In that case, water leaking from the shower on the opposite side of the brick wall had resulted in the masonry being too 'crumbly' to accept any anchors, and I was not comfortable with the box moving every time a plug was inserted into the receptacle.
(Not to worry- the leak had been solved, but the owner was not about to replace the entire wall!)
I am not all that concerned about any reaction between the foam and the cable jacket. Those foams are like an epoxy; rather than a solvent, they contain two materials that react with each other. Oddly enough, the "second" component is sometimes moisture in the air!
That aside, the liberal use of foam is, in my experience, a sure sign of a third-rate contractor. Foam is not cheap, either. I might not be able to cite for the use of foam ... but I sure can take that as a hint to look closer!
Over the years I have run into so many non-metallic boxes secured in block or brick wall with some type of grout added and the box pushed into it to secure the box. I wonder what amount of that substance, contaminates the romex sheath. I did it myself for a long time. Now I use spray can expanding foam to hold the box in the wall. It has worked out excellent, none have worked loose. My feeling is that it is alot better on the cable than a caustic cement. Even better is to run pvc down the void of the block if it is possible, but a lot of remodel does not allow for that.