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#100339 - 11/13/06 07:50 PM Mounting Stuff  
jes  Offline
Joined: Jul 2002
Posts: 103
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?

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#100340 - 11/13/06 08:41 PM Re: Mounting Stuff  
Zapped  Offline
Joined: Oct 2002
Posts: 482
Huntington Beach, CA, USA

I have never heard of a foam designed for, tested for, or listed for the securing of ANYTHING electrical. It may exist, but not in my world.

Read through all the NEC codes about proper mounting and retention, and you'll find a lot of "designed for...", "listed for the use as...", etc.

If anyone knows an inspector that would pass such a thing, I owe you a cold one.

#100341 - 11/13/06 09:48 PM Re: Mounting Stuff  
macmikeman  Offline
Joined: Jul 2002
Posts: 717
Honolulu, Hawaii
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?

#100342 - 11/13/06 10:38 PM Re: Mounting Stuff  
BigB  Offline
Joined: Mar 2004
Posts: 721
Tucson, AZ USA
I have not seen it used in conventional construction, but in mud adobe it is used here all the time and passed all the time. There isn't really a better way to secure boxes in mud adobe.

#100343 - 11/14/06 05:20 AM Re: Mounting Stuff  
iwire  Offline
Joined: Jan 2003
Posts: 4,391
North Attleboro, MA USA
I don't see anything in the NEC that would prohibit this.

Bob Badger
Construction & Maintenance Electrician

#100344 - 11/14/06 09:33 AM Re: Mounting Stuff  
Zapped  Offline
Joined: Oct 2002
Posts: 482
Huntington Beach, CA, USA
Looks like I'm going to have quite a bar tab.

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.

Happy hour, anyone?

#100345 - 11/14/06 06:01 PM Re: Mounting Stuff  
Tom  Offline
Joined: Jan 2001
Posts: 1,044
Shinnston, WV USA
The securing & supporting is covered in 334.30 and I see nothing there that specifically allows this type of installation.

However, an inspector can accept other methods (90.4 second paragraph). If I was inspecting, I would want some substantiation that the foam would not harm the cable (110.11).

Few things are harder to put up with than the annoyance of a good example.

#100346 - 11/14/06 07:18 PM Re: Mounting Stuff  
George  Offline
Joined: Feb 2002
Posts: 375
It appears that such work is cod ecompliant.

The NEC should reconsider the use of NM cable in blown foam insulation in walls but until they do ...

#100347 - 11/14/06 09:08 PM Re: Mounting Stuff  
renosteinke  Offline
Cat Servant
Joined: Jan 2005
Posts: 5,316
Blue Collar Country
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!

#100348 - 11/14/06 11:39 PM Re: Mounting Stuff  
macmikeman  Offline
Joined: Jul 2002
Posts: 717
Honolulu, Hawaii
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.

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