Spray foam over NM cable

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  #1  
Old 05-15-15, 08:02 PM
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Spray foam over NM cable

I'm planning on applying spray foam insulation over new NM cable. Should the NM be OK if it's encapsulated in spray foam (no corrosion of the cable, etc)? Is there a requirement for derating the cable? If it were you, would you spend the extra time and money on ENT, to keep the foam off and allow for future cable pulls if needed?
 
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Old 05-15-15, 08:24 PM
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If it were you
If it were me I'd use cellulose.
 
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Old 05-15-15, 08:29 PM
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Due to its properties as an insulation, or due to its interaction with the electrical side of things?
 
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Old 05-15-15, 08:37 PM
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Due to its properties as an insulation, or due to its interaction with the electrical side of things?
With the assumption that this is in an attic my answer would be "Both". There is no way I'd fill my attic with foam that would restrict my access for running new circuits, installing new lights or ceiling fans from above or venting a bath exhaust fan in the future. As far as interaction with the PVC jacket on the NM cable, I don't think it would be a problem, but I also couldn't swear to it. If this is up against a roof deck, I would reconsider as long as it was a closed cell foam.
 
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Old 05-15-15, 09:01 PM
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Fair enough. It's an exterior wall on the top floor of the house. Unfinished attic above, and the room below already has updated electric (relative to the 1890 build date of the home at least - grounded NM with appropriate receptacle spacing). I'm not foreseeing a need to fish any more cable through the insulated walls, but you can't ever be 100% sure.

The attic has a combination of blown rock wool and fiberglass rolls, and I don't think that's going to be replaced any time soon, for many reasons.
 
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Old 05-16-15, 07:28 AM
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Damage

Deleted post. Already answered.
 

Last edited by Wirepuller38; 05-16-15 at 07:29 AM. Reason: Deleted post.
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Old 05-16-15, 08:44 AM
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It's an exterior wall on the top floor of the house
I had made the assumption that the application was in an attic because you hadn't said where the foam was going. In a wall I think foam would be alright, but cellulose would also work. As far as a problem with the foam on new NM-B cables, I cannot say, but suspect the foam manufacturer has some data on this. Many of the newer foams are water based and probably wouldn't affect the cables.
 
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Old 05-16-15, 10:21 AM
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A custom home builder just a built a new home behind mine. The entire house was spray foamed.
 
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Old 05-16-15, 01:04 PM
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Your wire will be fine, but as you seem to be aware of, good luck running new circuits in later on.
I personally don't mind overkilling things in my personal space, so I would run a ton of extra receptacles, data jacks, and pipe key areas.
Look at your rooms and envision every feasible possibility for how you would arrange furniture. Have a data jack and receptacle across from ever place you envision a bed (possibility of a tv), and at every place you could envision putting a computer desk (internet access). Toss a receptacle every 5' along walls if you like. Pipe up to an attic box for switch banks. Envision where you would plug in your vacuum, a heater, or any high draw appliances and make those dedicated receptacles. Run "future tubes" from the basement to the attic for easy runs later on.
Receptacles and jacks are cheap and cost you nothing just sitting there unused. Go nuts with them and foam away.
 
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