I'm redoing my basement and I have put in some of the rigid pink insulation boards on the wall. So far, I've attached the boards to the wall, and built a frame (1 1/2") on top of that. I'm planning on putting more of the boards in between the framing studs before doing a vapor barrier and dry-walling. My problem right now is that I want to add an outlet near the bottom of one of the walls... So, I have to run a wire through the wall to the electrical box...
I'm wondering if I should be doing anything special around the wire and/or the electrical box when doing this.
I didn't think you needed to derate cables in residential construction unless you have bundles of cable. Around here, you are encouraged to insulate as much as possible...no issues with insulating against modern electrical cable. The exception would be if you had old-style wiring (the type where the sheathing was prone to flake off over time).
Foam board acts as a continuous vapor barrier with no thermal "short circuits" from the studs. Any time you calculate the actual insulation value you always have to allow for the framing. A 2x4 has an R value of ~1/inch, or 3.5, and the studs take up around ten or fifteen percent of the wall.
The preferred method and amount of insulation is dependent on climate, as well. You want to make sure that there's only one vapor barrier, and you're not trapping moisture in between two vapor barriers. One layer of foam, and either a stud wall with just drywall, or with unfaced batt insulation between the joists (allowing the foundation walls to dry to the interior) is preferable to two layers of foam.
XPS foam (generally blue/pink) is superior to fiberglass batts in R- value and also forms a pretty good vapour barrier if you're careful with it. It doesn't absorb water, so putting it directly against concrete walls seems like a great idea...any moisture will run down the outside rather than rotting your studs. Assuming you have a place for the water to go, that is. You've generally got to cover it with a 15-minute fire barrier (1/2" drywall, plywood, etc.).
XPS offers about 30% - 45% more R-value per inch. Also costs quite a bit more.
Yes, I was originally going to do foam board, and then use vatting between the studs, giving me an R-Value of around 19. But then the wife found out I was going to go 6" into the room to do that, and, after a bit of deliberation, we decided to do just 1 1/2" foam board, and a 1 1/2" frame on top of that (Already bought the 2x4's, so I just turned those sideways...). I would put the vat insulation between the studs, but I didn't see any made for 1 1/2" (maybe I'll look again), as the regular insulation is WAY cheaper. But yes, the foam board does have a higher R-value per inch than vat, and has a much higher R- value when you consider the 2x4's in your equation (the advertised R- value on vat is the R value of the insulation, and does not take into account the 2x4). As far as moisture, I'm not vapor-barring the space between the floor and the insulation or the space above, so I figure the water will have somewhere to go (and no, the frame is not resting on the concrete floor, so I'm not scared of rot there).
I'm concerned about the wiring for the reason mentioned above -- do I want to insulate a hot cable. While I expect the circuit breaker would flip before the wire gets to the magic temperature, I don't want to build something that has the potential to do some serious damage if things went really wrong (say a nail shorted the wire and the breaker didn't flip or something like that). I'm thinking maybe I'll cut a channel in the foam, and put regular vat insulation in there, and run the wire through that.
It's called batt insulation, vat is what they keep the wine in while you're installing the batts.
As far as worrying about insulating around wires...have you ever seen an exterior wall that didn't have wires running through it? It's not a problem, so don't worry about it.
Really, the right thing to do is check with your code enforcement office since they get the last word on everything anyway. Also a few searches on your favorite search engine can help, too. There is no one-size fits all answer here. As soon as wire hits 75 to 80 % of its specs, ambient heat buildup begins. Insulate that and of course the heat buildup increases if the heat has no place to go. That's why you see all the splits & butt ups, in residential rules.
Following is only one of many things that relate to this stuation. There isn't just one answer.
======
- - - The ampacity of Types NM, NMC, and NMS cable shall be determined in accordance with 310.15. The ampacity shall be in accordance with the 60°C (140°F) conductor temperature rating. The 90°C (194°F) rating shall be permitted to be used for ampacity derating purposes, provided the final derated ampacity does not exceed that for a 60°C (140°F) rated conductor. The ampacity of Types NM, NMC, and NMS cable installed in cable tray shall be determined in accordance with 392.11.
- - - Where more than two NM cables containing two or more current-carrying conductors are installed, without maintaining spacing between the cables, through the same opening in wood framing that is to be fire- or draft-stopped using thermal insulation, caulk, or sealing foam, the allowable ampacity of each conductor shall be adjusted in accordance with Table 310.15(B)(2)(a) and the provisions of 310.15(A)(2), Exception, shall not apply.
- - - Where more than two NM cables containing two or more current-carrying conductors are installed in contact with thermal insulation without maintaining spacing between cables, the allowable ampacity of each conductor shall be adjusted in accordance with Table 310.15(B)(2)(a).
Table 310.15.(B)(2)(a) is the derating table.
Thus, first there is the derating for ambient - which ALWAYS applies and ALWAYS applies first (in severe cold climates, derating still "applies", it is just that there is no derating "to apply"), then the derating for bundling or lack of maintaining spacing applies, AND, if there is no bundling or lack of maintaining spacing - which is what triggers Table
310.15(B)(2)(a) in 334.80 Ampacity - then there is no harm and no foul.
This tells me that they ran tests and determined that, as long as the cables are spaced out, they are suitable for the same ampacity in thermal insulation. That is because the NM-B uses 90 degree C rated insulation, which apparently can withstand the accumulated heat of normal allowable current flow within the conductor. The normal allowable current flow in a #12 is 20 amps overcurrent protection, with normal less than 80% on the circuit if a continuous load, if not a continuous then there will not be the same heat build-up to be concerned with. __________________ ==========
Yes. That's why you see in the regs to split the foam and butt it, rather than just let it all be insulated; the heat needs a place to dissipate to. See previous post for some references instead of just words of opinion.
What HTH? The plagiarism? At least have the courtesy of linking to information you cut and paste.
formatting link
It's not so difficult.
Oh, and while you're pilfering stuff to make your point, don't be a dweeb and leave out the part that directly contradicts what you're trying to say - and from the same expert source! There's a word for that and it's called lying. You omitted this part:
" Re: Wiring in spray foam insulation Quote: Originally Posted by bob smit Jerry, thanks for reminding me about that new addition to art 334.80 (2005) however, u failed to include "where bundled togeather" when passing thru framing members to be insulated. Bob, I didn't forget that as you are referring to the paragraph above the one I highlighted. See below in red for what you are referring to. Quote: If the cables are not bundled togeather between the studs then this derating requirement would not apply."
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.