Urethane foam and NM cable

[copper123]

I have wanted to ask this question for a long time.
Does anybody have a final verdict on the question of Urethane foam and using it around wiring? I have always been told that with no circumstance can NM cable (Romex) be encapsulated in a foam type application. Heat is a certain reason, but the other is the fact that romex has no long term testing with exposure to urethane. Does this sound familiar? A very common application in our area for foam is in the Rim Joists. A lot of contractors spray foam at the joist to make a good tight seal. Any NMC that goes vertical down the stud cavity and then up into the joist space passes through the rim. One inspector makes us wrap all the wires in newspaper before they spray the joist. Just wondering what others have found. I ask, because I saw a ?This old house? and the contractor sprayed the entire house with Urethane and encapsulated all the newly ran NMC. Maybe this is common back east?
Thanks

 

[PlnOldRick]

Re: Urethane foam and NM cable

are you talking about isonene/isocyanate?

none the less what the hell is romex wrapped in newspaper going to do? other then provide more to burn when the wire does overheat and ignite. sounds like a bad idea for a potential non-problem!

 

[copper123]

Re: Urethane foam and NM cable

yes, that is what we are talking about. What the inspector is looking for is a very loose wrap around the conductors. Basically you are making a 2" conduit that gets no foam. This keeps the foam off the wire, and it also keeps it from encasing it. Also, I have been told that the spray foam process is extremely hot. The temperature of the material after being sprayed can be up to 180 F.? Keep in mind, this newspaper application is only at the rim joist space. Very little of the wire ever needs to be wrapped.

[ January 16, 2006, 11:02 PM: Message edited by: copper123 ]

 

[tom baker]

Re: Urethane foam and NM cable

On This Old House last week, they were showing applying the spray on foam, that almost instantly expands to fill the stud bay. It was shown being installed around an electrical box.

However the NEC does recognize that sealing foam is used around NM at a top plate and there is a 2005 NEC change concerning this, see 334.80 last sentance.