It's been a while since I've had to ask a question here, now that I have retired from the EC business. (and my other job as a Civil Aviton Inspector as well - it's nice to get older and retire).

However, once the neighbours know about your past, I get questions and asked for advice about electrical installations. One of them has me flummoxed since I had not run into this one before.

He is doing a new basement installation to add a new living space in the basement and the 2X6 walls are being wired for all kinds of stuff including CAT 5 and every other kind of who knows what its for, cable including the basic electrical outlets, switches and fairly elaborate lighting system in a suspended ceiling system.

However there are a few places where 4 NMD 90 cables could be run up the 2X6 studs from just above the concrete floor level to the ceiling and these are on outside walls that he would like to spray with foam insulation.

I have checked both the CEC and NEC codes ad nauseum, about spraying insulation into the interior of the wall stud cavities and can find about zero information about any requirement to derate the cables for that kind of insulation. We all know about the usual batt insulation stuff but it seems to me that maybe the same rules that might not apply since there is no air flow in spray insulation as in fiberglass or rockwool insulation.

Has anyone here have information, experience or a code requirement about spray foam insulation applied on outside walls that require derating of the conductors?

The NEC does not differentiate between fiberglass or spray in foam. If you look at 334.80 in the 2008 NEC, the last paragraph requires an ampacity adjustment.

If you do the ampacity adjustment, you'll start in the 90 degree column and adjust that with a 70% multiplier for 8 current carrying conductors. That works out to 21 amps for #12 and 17.5 amps for #14, both of which exceed the maximum circuit breaker size for both sizes.

I'd say that there is no problem running 4 two conductor cables.

Tom

[quote=Tom]The NEC does not differentiate between fiberglass or spray in foam. If you look at 334.80 in the 2008 NEC, the last paragraph requires an ampacity adjustment.

If you do the ampacity adjustment, you'll start in the 90 degree column and adjust that with a 70% multiplier for 8 current carrying conductors. That works out to 21 amps for #12 and 17.5 amps for #14, both of which exceed the maximum circuit breaker size for both sizes.---


My guess is it will soon. My only caution with the foam is,it gets hot as it cures,so any low volt use a good PVC/Poly insulation.I have had times where the cheap typical phone cable has sufferd damage.
I'd say that there is no problem running 4 two conductor cables.

I would be more concerned if the the foam would react with the rx insulation.

Ob

Yes, conduit seems like a good idea. Some kinds of foam insulation (particularly the stuff sold in small cans to the homeowner) are supposed to react with PVC and soften it. Better safe than sorry!

Over here in New Zealand we use a different grade of PVC cable for these sorts of installations.
It's called Non-Migratory PVC.
Here's a link to the manufacturers specification:

Clicking this link will open a PDF file

Derating of Romex cable starts at the rating of the cable: 60 degrees Centigrade.

This reduced rating vs the underlying THWN-2/ or THHN reflects the fact that the cable sheath insulates...

The rise in super-insulated homes may well cause the Code Committee to revisit this issue. But as it stands, no NEC provision exists to derate based upon spray in foam. For my money it should be treated as if were running underground.

1981- 2010- derated once.

Never ever to this day had a problem. In any application.

If you watch any of the Mike Holmes renovations shows from Canada if he has an open outside wall open on the inside, he foams it.

I am sure I have seen him order foam for existing walls with the old "fabric" romex, and you know how anal he is about doing things to right to code.

As far as I can tell, the derating requirements of 334.80 only apply to more than two NM cables with two or more current carrying conductors if you don't maintain spacing.
IMO, since the spacing is not defined, it could be 0 to 1mm or even 10-feet... there is no specific distance required top to bottom, or side to side, whether thermal insulation is involved or not. Likewise when any number of NM cables is installed through the same hole in wood framing whether it is to be draft stopped or not.
So, I guess if you have metal framing... no worries?

The way I see it, you could drill a single 1-1/4-inch hole in a wood top plate and run as many NM cables through it as will fit without derating, as long as the cables are evenly stacked top to bottom and side to side. There also doesn’t appear to be anything preventing you from changing direction of the cables to a different position once they pass thought the hole in the framing, as long as they all transition in the same direction with the same spacing, which in this case, could be any desired amount.

I don't write it... I just read it.

I did find "some" guidance here, but it still does not seem clear to me.

2-122 Use of thermal insulation

(1) Where the hollow spaces between studding, joists, or rafters of buildings are to be filled with thermal insulation, the following restrictions, as applicable, shall apply to the installation of electrical wiring in such spaces:

(a) special care shall be taken to ensure that conductor insulation temperatures are not exceeded due either to mutual heating of adjacent conductors or cables or to reduced heat dissipation through the thermal insulation;

( b) if the space is to be filled with a loose or free-flowing material that is non-corrosive, fire-resisting, and non-conductive and that is in compliance with the National Building Code of Canada, any type of wiring system recognized by this Code shall be permitted to be used, but special care shall be taken to ensure that there will be no strain on the conductors due to the weight or pressure of the insulating material;

(c) if the thermal insulation material, in the form of batts or rigid sheets, is installed prior to the installation of the wiring and secured in place so that there will be no undue pressure on the conductors, no special precaution need be observed;

(d) if thermal insulation made of or faced with metal is installed, the wiring shall conform to the following:

(i) a 25 mm separation shall be provided between the thermal insulation and the knob-and-tube wiring; and

(ii) non-metallic-sheathed cable may be in contact with the insulation; and

Δ (e) mineral-insulated cable, aluminum-sheathed cable, or copper-sheathed cable shall not be used with types of thermal insulation that are liable to have a corrosive action on the sheath.


It appears that 2-122 (1)(a) might apply here. Unfortunately the requirement to derate the cables is still a complete mystery to me. Unless I'm a complete idiot at looking at the Canadian Electrical Code, the term "special care" comes up quite often, but I have never seen a definition of that.

I'm going cross-eyed at reading the Canadian Electrical Code over and over again.

Maybe common sense would take care of those words "special care" but lately "common sense" is not an acceptable way of thinking according to most lawyers.

Anyone have any further thoughts here?

spacing would be a AHJ call

I would like to agree with you, but where is that written in NEC 334.80?
To be honest, I don't even see any "spacing" requirements listed in 310.15 for raceways, single or multiconductor cables, AC or MC, even where bundled or installed in lengths over 24-inches.
All I see is that the spacing, of whatever amount you begin with, must be maintained throughout the run, even when making bends.
On the upside though, for the purpose of derating in Table 310.15[B]2,a, the neutral conductors of 3-wire multiwire branch circuits are not counted as a current carrying conductors, which may help keep the wire count down in some instances.

The inspector I spoke with said its not the spacing distance that he is concerned with but the method of maintaining that distance.

If you're interested in an outside view... most European codes require derating for bundling when the cables are spaced closer than their own diameter (i.e. if you leave once the cable diameter in between two cables it's not bundling).
For wiring run in insulated walls there are no derating factors but in fact whole different ampacity tables, called installation methods. These cover wiring in conduit in non-insulated walls (either masonry or stud walls), insulated walls (type of insulation not specified), direct burial of cables in masonry walls, direct burial underground and wiring in free air (overhead lines), giving different ampacities for each method and cross section.

Usually the difference is pretty small, but when said difference is hovering around a breaker size it can be important (like if you have an ampacity rating of 15.7A you can't use a 16A breaker any more, but with 16.3 you can).

Since the maximum allowed fuse/breaker rating under normal conditions is specified a lot more conservative by the NEC than by any other code I know derating might not be as much of an issue anyway, but that's just an educated guess.

I think that some of you have gone off on a tangent.
The OP wanted to know about derating cables running through spray foan insulation. Not derating cables when bundled.
The CEC has clear rules for derating cables when bundled.

As for derating when run through spray foam insulation, I have worked on houses where the walls were going to be spray foamed and I didn't worry about the derating because I never load my circuits up to the max. For example the CEC allows 12 receptacles per circuit, but I never put more than 10 on a circuit. So in effect I guess you could say that I automatically derate by 16%.
I don't believe that a rule exists in Canada at this time concerning running conductors through spray foam insulation.

I was hoping that mikesh would have contributed by now. It would be interesting to hear an inspectors opinion on this.

Of course if I'm wrong and the OP was concerned about derating when bundling, then just ignore this whole post.