Open Cell Foam with NM-B cable...

[EEEC]

BAYSEAL OC Light Density - Open Cell Foam with NM-B cable

The following document (link) shows that it is permissible, but with certain restrictions with regard to the wiring methods. I have a few questions that directly pertain to this as well as some other general questions while I'm at it...

https://www.nema.org/Technical/Documents/Bulletin%2095%20Rev%202007%20NM%20Cable%20encased%20in%20spray-foam%20insulation.pdf

First:


334.10(3) Other structures permitted to be of Types III, IV, and V
construction. Cables shall be concealed within walls,
floors, or ceilings that provide a thermal barrier of material
that has at least a 15-minute finish rating as identified
in listings of fire-rated assemblies.

When it refers to ceilings, it refers to the interior ceiling "covering", correct? Last I checked a ceiling is a ceiling, an attic is an attic, and a roof is a roof. Does it have to be an enclosed bay or can there be crawl space so long as the interior ceiling is 15 minute rated? I would think so, based on 334.23 (and therefore 320.23, followed by 300.4[D]). Someone is essentially trying to say that the NM-B needs to have a 360 deg 15 minute thermal barrier...


Next:

Section 334.80 requires ampacity adjustments for NM cables bundled and run through a bored hole that will be filled with insulation and for more than two NM cables that are installed in contact with thermal insulation without maintaining spacing between cables. Section 334.80 states that where more than two Type NM-B cables are run through a bored hole that is to be fire or draft stopped using thermal insulation or sealing foam, the ampacity must be adjusted. Section 334.80 also states that 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).


I've read several threads on this forum in regard to this and there are so many varying explanations that I'd like a cut and dry confirmation of what I've learned. True or False?:


1) There is no specification for the distance of "spacing".

In my opinion they should change it to "not in contact" instead of "maintain spacing". A micron is a "space" under a microscope, but I doubt that would be enough "space".


2) "...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...".

I read this as: one 8/2 in contact with an 8/2 requires no derating. But an 8/2 in contact with an 8/3 requires derating.


Finally:

Regardless if it is politically correct, or wrong, or whatever, on many tract home jobs where one of the main concerns is "hurry up!", many apprentices are taught "rule of thumb" do's and don'ts without an explanation as to why. For instance, "It's okay to run up to three wires through a bored hole, but you can only put two wires under a staple." I searched the entire 2014 NEC for the word "bored" and couldn't find anything that would explain this "rule of thumb". I thought that maybe this was derived from 334.80. Any takers?

 

[EEEC]

I think I may finally have a grasp on this whole derating thing. Can someone tell me if I've got it right?


So let's say I have three NM-B cables, a 10/3 and two 12/2, running through a bored hole that will get spray foamed (or not). I have 7 current carrying conductors. According to 310.15(B)(3)(a), I will need to derate by 70%. According to 310.15(B)(16) the 90 deg #10 (the "B" designation in "NM-B" says it's a 90 deg conductor and it sure as heck resembles a single, solid, THHN wire by the way) wire is rated up to 40A. 40A * 70% = 28A. Therefore this 10/3 cable has to be placed on a 20A breaker. Next, the 12/2's based on the same temp rating principles would be 30A * 70% = 21A. And even though the logical assumption would be to place these cables on 20A breakers, because there is no such thing as a 21A breaker, the fact of the matter is that according to 240.4(D), the maximum overcurrent protection device allowed for a #12 conductor is 20A. In other words, even though a 90 deg rated #12 wire can easily handle 30A, the NEC requires the OCPD to be sized no greater than 20A.


I think this is where the "three wires in a hole" comes from. Since the most common wires in a single family dwelling is 14/2, 14/3, 12/2, and 12/3, any combination of any three of these NM-B cables will not restrict the breaker size.

I'm still not sure why only two cables are allowed to be stapled together...

Also, I think I've figured out why they use the term "maintain spacing" and don't use "not make contact" for two reasons. One, if you have several NM-B cables stapled near one another across a truss, they are bound to "touch" each other. But as long as they don't touch each other continuously for 24" (by maintaining space), they are not considered "bundled" and therefore are not subjected to derating based on:

310.15(B)(3) Adjustment Factors. (a) More Than Three Current-Carrying Conductors. Where the number of current-carrying conductors in a raceway or cable exceeds three, or where single conductors or multiconductor cables are installed without maintaining spacing for a continuous length longer than 600 mm (24 in.) and are not installed in raceways, the allowable ampacity of each conductor shall be reduced as shown in Table 310.15(B)(3)(a). Each current-carrying conductor of a paralleled set of conductors shall be counted as a current-carrying conductor.

 

[david]

BAYSEAL OC Light Density - Open Cell Foam with NM-B cable

First:

When it refers to ceilings, it refers to the interior ceiling "covering", correct? Last I checked a ceiling is a ceiling, an attic is an attic, and a roof is a roof. Does it have to be an enclosed bay or can there be crawl space so long as the interior ceiling is 15 minute rated?"

The concern is subjecting the cable to physical damage. The NEC deals with the environment and conditions that subject a wiring method to physical damage many times as a judgement call for the authority to make.

However this is what you would call a prescriptive rule stating that a NM cable exposed is to be considered subject to being damage. The rule is saying NM cable cannot be run exposed.

In other words you cannot install it in a location that would expose the cable without removing the buildings finish to get to the cable

 

[david]

BAYSEAL OC Light Density - Open Cell Foam with NM-B cable



In my opinion they should change it to "not in contact" instead of "maintain spacing". A micron is a "space" under a microscope, but I doubt that would be enough "space".


2) "...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...".

I read this as: one 8/2 in contact with an 8/2 requires no derating. But an 8/2 in contact with an 8/3 requires derating.

An 8/3 with ground has at least two current carrying conductors.

you can have two cables but not three

 

[david]

BAYSEAL OC Light Density - Open Cell Foam with NM-B cable

Finally:

", many apprentices are taught "rule of thumb" do's and don'ts without an explanation as to why. For instance, "It's okay to run up to three wires through a bored hole, but you can only put two wires under a staple."

The first issue is bundling in bored holes and derating

the second is the length of a stable after two cables you most likely would smash or damage the cable to get a staple to hold.

I did work for a contractor that had bought five gallon buckets of staples that where longer for that reason

 

[infinity]

You need to keep the number of CCC's to 9 or less with #14 and #12 cables in a sealed hole to avoid having derated value that is lower than the standard ampacity of 15 and 20 amps. It's that simple.

If there are two cables in the sealed hole than no derating applies even if you have more than 3 CCC's. Four 14/3 or 12/3 cables in most installations will be only 8 CCC's which means that four cables in the sealed hole is the practical limit if you don't want to bother worrying about a derating calculation.

 

[david]

The concern is subjecting the cable to physical damage. The NEC deals with the environment and conditions that subject a wiring method to physical damage many times as a judgement call for the authority to make.

However this is what you would call a prescriptive rule stating that a NM cable exposed is to be considered subject to being damage. The rule is saying NM cable cannot be run exposed.

In other words you cannot install it in a location that would expose the cable without removing the buildings finish to get to the cable

"that provide a thermal barrier of material that has at least a 15-minute finish rating as identified in listings of fire-rated assemblies."

In a un-finished basement or accessible attic an electrician who has over looked this rule may look for a solution to conceal the cable, rather than replace the cable, it would have to be 1/2 dry wall or something other than cardboard that would provide a 15 min. fire rating

 

[EEEC]

I appreciate you helping out, but I think you're mixing apples with oranges in regards to my specific question. My first question is based on permitted NM cable uses within certain building types, while you are referring to protection of the NM cable itself. I know they go hand in hand, but we all know the verbiage varies and has other meanings depending on what specific topic they are referring to.

Original Question:

334.10(3) Other structures permitted to be of Types III, IV, and V
construction. Cables shall be concealed within walls,
floors, or ceilings that provide a thermal barrier of material
that has at least a 15-minute finish rating as identified
in listings of fire-rated assemblies.

When it refers to ceilings, it refers to the interior ceiling "covering", correct? Last I checked a ceiling is a ceiling, an attic is an attic, and a roof is a roof. Does it have to be an enclosed bay or can there be crawl space so long as the interior ceiling is 15 minute rated? I would think so, based on 334.23 (and therefore 320.23, followed by 300.4[D]). Someone is essentially trying to say that the NM-B needs to have a 360 deg 15 minute thermal barrier...

"that provide a thermal barrier of material that has at least a 15-minute finish rating as identified in listings of fire-rated assemblies."

In a un-finished basement or accessible attic an electrician who has over looked this rule may look for a solution to conceal the cable, rather than replace the cable, it would have to be 1/2 dry wall or something other than cardboard that would provide a 15 min. fire rating

I believe I read that the "accessible attic" you are referring to it one that is defined in the code as having a permanent stairway or ladder, and just because it has an access or scuttle hole doesn't automatically make the cable within the attic space exposed to damage. In the case that there is a simple access hole, the cable needs to be protected by running boards in an area within 6ft of the access. See 320.23(A).

However this is what you would call a prescriptive rule stating that a NM cable exposed is to be considered subject to being damage. The rule is saying NM cable cannot be run exposed.

Actually, it can so long as it follows:

334.15 Exposed Work. In exposed work, except as provided in 300.11(A), cable shall be installed as specified in 334.15(A) through (C).



So again, I believe the 15-minute thermal rating for a ceiling is in reference to an interior barrier. Does anyone agree?