NM cable protection

nizak

Senior Member
Curious as to thoughts on the following.

Would NM cable that’s concealed behind 3” of spray foam be considered protected.

This is an application where the NM is stapled horizontally 6’ off the FF.
Its is running across purlins 8’ between the 6”x6” posts of a pole barn.

Customer may not choose to finish the interior therefore leaving the NM in the condition mentioned.


I know there’s several ways to avoid this but this particular application is what I’m asking about.

Thanks
 
If it's not completely enclosed, could it be considered a damp or wet location? According to the NEC, it's what the "location" is determined to be, not that the wire may or may not be exposed to. For instance, a PVC sleeve from the the soffit going down to a hot tub disconnect. You couldn't use 6-3 NM cable in this short piece of PVC on the outside of the building. See NEC 300.9 It's not that the cable itself would ever get wet, but the inside of said conduit is considered a wet location. Don't shoot the messenger, I didn't write this stuff! LOL
 
Also, the R-value of spray foam is at least twice that of fiberglass. I could see some potential heating issues.

Mark
 
Just no question I would personally reach for MC purely to create a conduit channel where you could potentially fix something. With NM, you have zero option other than destroy the foam.

Just my thought. I'm not a fan of NM in barns.
 
Also, the R-value of spray foam is at least twice that of fiberglass. I could see some potential heating issues.

Mark
There has been that conversation ad nauseum around here for years pertaining to NM cable being encapsulated.

Even spoke with State Inspectors and no one has any concerns.

I make a point to box off the area above my panels where all the home runs come in so they don’t get spray foamed into one big mass.
Worst case if GC complains about lack of insulation against the bond board I’ll push some fiberglass loosely around it.

I don’t know of any other local guys who do it. Inspectors approve new builds daily where the spray foamed is up to 6” thick and all you see at the top of the panel is about 1” of NM cable.
 
Also, the R-value of spray foam is at least twice that of fiberglass. I could see some potential heating issues.

Mark
The ambient temp factors were added to the code because of the fear that wires on rooftops were getting too hot. Thing is, I don't see any rooftops with 50+ years of wire sitting in the hot sun overheating and failing. NM protected in insulation can't be getting that hot.
 
Just no question I would personally reach for MC purely to create a conduit channel where you could potentially fix something. With NM, you have zero option other than destroy the foam.

Just my thought. I'm not a fan of NM in barns.
Of all the reasons to use MC being able to pull wire in and out of the sheathing isn't one of them.
 
The ambient temp factors were added to the code because of the fear that wires on rooftops were getting too hot. Thing is, I don't see any rooftops with 50+ years of wire sitting in the hot sun overheating and failing. NM protected in insulation can't be getting that hot.
When I started wiring houses in '82, the conductors in the NM cable were covered with TW insulation. That's 60 C or 140 F. This is in Orlando, FL where in the summer, I can pretty much bet that the temperature in the attic can exceed 140 F. This means that my 14-2 home runs in the attic can not have even .5 amp of current flowing through them without exceeding their temperature limitations. And here I thought I always did quality wiring jobs! :)
 
I do t have my book at moment but I bet there some gray area you can argue one way or another seems protected to me-
If it’s closed cell spray foam it’s water proof
I won't argue the fact that it would probably be fine for years. I just don't think there is an exception anywhere that says that NM cable can be used in wet locations. See NEC Art. 334.12 (B)(3) and (B)(4).
 
Would it be considered wet location if it’s emended in closed cell insulation since it’s water retardant?? I agree with you but if it was my job I would argue in what ever way I want my job to go lol

But I don’t think the op is a wet location is it??
 
Would it be considered wet location if it’s emended in closed cell insulation since it’s water retardant?? I agree with you but if it was my job I would argue in what ever way I want my job to go lol

But I don’t think the op is a wet location is it??
That is up to the AHJ. If it were an open pole barn, I'm considering it a wet location. Look at post #3. The inside of a conduit installed on the outside of a building is a wet location. My example show the only way the inside of the conduit gets wet is if the attic floods! It doesn't matter and sometimes it makes no sense. See Charlie's Rule!
 
but that’s the NEC definition for raceway wire embedded in close cell spray foam that’s not a raceway. If you frame a hollow cavity in post or a box around it with you consider that location it’s not a raceway so NEC doesn’t have any saying it
The whole thing about the code is fine ways to wiggle around and make your thing work really doesn’t give a crap about safety. It’s just about compliance With an authority..

I get your point though—
 
(1) NM cable behind 3" of spray foam would be fine with me.

(2) Spay foam must be covered by either a "thermal barrier" or an "ignition barrier" because when it burns, it produces copious amounts of hydrogen cyanide and other nasties that will kill you very quickly - so quickly that in the Station Night Club fire, they found bodies in the dining area that were still seated at the dinner table. See the "Foam Plastics" sections of the IRC and IBC. Foam is also a petroleum based product that turns into melty-sticky napalm when exposed to fire. "Thermal barrier" or "ignition barrier" means drywall or similar.

If there is an area where the foam is allowed to be exposed (I have never seen one), then the NM cable is in no danger because it would never have any people anywhere near it.

Watch bundling, when you are in insulation, you can't have more than 4 NM cables in 12 or 14 gauge wires touching each other anywhere.
 
(1) NM cable behind 3" of spray foam would be fine with me.

(2) Spay foam must be covered by either a "thermal barrier" or an "ignition barrier" because when it burns, it produces copious amounts of hydrogen cyanide and other nasties that will kill you very quickly - so quickly that in the Station Night Club fire, they found bodies in the dining area that were still seated at the dinner table. See the "Foam Plastics" sections of the IRC and IBC. Foam is also a petroleum based product that turns into melty-sticky napalm when exposed to fire. "Thermal barrier" or "ignition barrier" means drywall or similar.

If there is an area where the foam is allowed to be exposed (I have never seen one), then the NM cable is in no danger because it would never have any people anywhere near it.

Watch bundling, when you are in insulation, you can't have more than 4 NM cables in 12 or 14 gauge wires touching each other anywhere.
Reallly foam insulation, has to all be covered. I did not know that. Doesn’t matter if it’s close cell or open cell.
 
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