Derate NM Cable through top plates of garage

[jar546]

Re: Derate NM Cable through top plates of garage

602.8 #4 certainly applies, no gray area there at all.

The space around the wires will be filled and sealed off. Derating is required.

I am not saying this is an NEC violation for doing this, just that it must be derated because of the way they did it.

Rough wire was not complete at this point and many more wired to get pulled. I was called out to this one too early.

This wording right hear takes the concealed interpretation out of the equation:

and between a top story and the roof space

 

[TimNY]

Re: Derate NM Cable through top plates of garage

602.8 #4 certainly applies, no gray area there at all.The space around the wires will be filled and sealed off. Derating is required.

I am not saying this is an NEC violation for doing this, just that it must be derated because of the way they did it.

Rough wire was not complete at this point and many more wired to get pulled. I was called out to this one too early.

This wording right hear takes the concealed interpretation out of the equation:

and between a top story and the roof space

I'm not sure if you are talking about this scenario or our off-topic scenario. I agree with you 100% on this actual scenario (my faux pas on the "violating NEC" comment).

If this were not a concealed space I would not agree that the top plate needs to be firestopped and therefore the wires derated. But I'm not sure if you were referring to my posts.

Tim

 

[Mule]

Re: Derate NM Cable through top plates of garage

Gotta disagree on this one fellers! I don't see how 3" of grouping the wire together would require derating. How about having a little bit of common sense. Think about it....how many times would these circuits actually be carrying a load at the same time? Maybe if by chance the electrician pulled a couple of kitchen circuits in the same hole and maybe if there were a couple of crock pots plugged in at the same time.

Some posters are just giving bits and pieces of the wording of the code without including the section number. Please include section numbers to support the wording. I'm going to research the snot out of this one! This is one reason I have my screen name....Mule...I'm a little stubborn!

EDIT!!! Been reading some of the sections quoted and I may have a hard time proving my point!

 

[GHRoberts]

Re: Derate NM Cable through top plates of garage

It is a garage wall that will be sheetrocked as there is a bonus room above. You are looking at the inside of the exterior garage wall that will be behind the bonus room kneewalls.George, trying to figure out the jarxxx thing. Why the x's? Easier to type? :?

I cannot remember your numbers. (Sorry, I will try to remember them.)

I don't think there is a problem but how about this for a fix:

Jam half of the wires against one side of the hole, jam the other half against the other side of the hole, use the fire stopping to hold them apart and in place.

 

[Mule]

Re: Derate NM Cable through top plates of garage

Not looking so good on proving my point!

George.....just a tip here. Even though when you click on "Post Reply" you can scroll down a little and all of the posts prior to yours are available to review. Just place your pointer in the box of the post of the previous person after you scroll down and you can scroll through the previous posters to look at any posters response.

 

[raider1]

Re: Derate NM Cable through top plates of garage

Mule,

Here is the NEC setion that requires that the wires in the picture have their ampacity adjusted in accordance with 310.15(B)(2)(a).

334.80:

334.80 Ampacity.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).

I added the bold to emphasize the part of that section with the requirement.

Chris

 

[north star]

Re: Derate NM Cable through top plates of garage

Mule,

You are killing me! :lol: I almost spewed coffee all over my screen and keyboard. I am still laughing...

 

[GHRoberts]

Re: Derate NM Cable through top plates of garage

George.....just a tip here. Even though when you click on "Post Reply" you can scroll down a little and all of the posts prior to yours are available to review. Just place your pointer in the box of the post of the previous person after you scroll down and you can scroll through the previous posters to look at any posters response.

I will try that. I usually hit quote and work from there. And one can only scroll down 1 or 2 posts. (It seems that if I hit reply I only get a couple posts also. I guess I need to change something in my profile. I will remember jar's (oops) number when necessary.)

 

[Heaven]

Re: Derate NM Cable through top plates of garage

My understanding is that there is no limit through a short distance such as a plate or two. NEC2008, I'd like to know if this is not the case.

 

[raider1]

Re: Derate NM Cable through top plates of garage

My understanding is that there is no limit through a short distance such as a plate or two. NEC2008, I'd like to know if this is not the case.

It is not the case. Again here is what 334.80 (2008 NEC) has to say about romex passing though a top plate that is to be fire or draft stopped.

334.80 Ampacity.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).

If you run 2 or more NM cables though a top plate that is to be fire or draft stopped you must adjust the ampacity in accordance with 310.15(B)(2)(a). You are permitted to start the adjustments using the 90 degree column of 310.16 provided that the final ampacity does not exceed the 60 degree column.

This typically means that the ampacity of the NM cable will be OK until you get more than 9 current carrying conductors run through the hole.

Chris

 

[Heaven]

Re: Derate NM Cable through top plates of garage

That's very helpful, thank you. But no limit for bored framing holes that aren't to be firestopped I gather?

The thermal insulation wording is very interesting as well.

 

[raider1]

Re: Derate NM Cable through top plates of garage

But no limit for bored framing holes that aren't to be firestopped I gather?

Correct, according to the person who purposed this change in the NEC there is evidence that sprayfoam insulation sprayed into the holes caused the NM cable to have problems dissipating heat.

Chris

 

[GHRoberts]

Re: Derate NM Cable through top plates of garage

Correct, according to the person who purposed this change in the NEC there is evidence that sprayfoam insulation sprayed into the holes caused the NM cable to have problems dissipating heat.

I have an outlet I use for my electric lawnmower - 20amp circuit, 12g wire, high quality recept. I use the circuit 2 hours continuous once a week. After 5-10 years I opened up the box and examined the wires. The insulation was discolored and had shrunk back 1/8".

My point is that code compliant installations have problems in dissipating heat.

It is doubtful that my recep or the wiring in the fire stopped holes will cause any problem beyond some insulation discoloration.

 

[Mango]

Re: Derate NM Cable through top plates of garage

I agree with "just Tim". Put some pookie in the holes and move on.

 

[raider1]

Re: Derate NM Cable through top plates of garage

I agree with "just Tim". Put some pookie in the holes and move on.

So you are saying just ignore 334.80? :roll:

Chris

 

[Mule]

Re: Derate NM Cable through top plates of garage

334.80 Ampacity.

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).

So IF the electrician placed something...toothpick, scrap wood, a piece of NM sheathing or whatever, so that a "space" was maintained, then the original picture posted would be within code?

How much "space"? 1/16?? Is there a code section that determines how much "space" is required?

I just don't see how grouping cables like this will be a problem. I know, I know, the code says........

We're talking a distance of 3 inches. How much heat could be generated within those 3 inches. I just don't see how this is a problem.........but......the code says.........

 

[GHRoberts]

Re: Derate NM Cable through top plates of garage

How much "space"? 1/16?? Is there a code section that determines how much "space" is required?

There are spacers called stackers that provide adequate spacing in wall cavities. They seem to maintain 1/8" space or so. But ...

(And I even found the little scroll device on the previous posts.)

 

[Span]

Re: Derate NM Cable through top plates of garage

Thank you,Mule. Is has been puzzling me for a long time. "How much space is mantain proper space"? when wires pass through bore hole or in coduit. Finally have some idea other than

derating and ambient temps.

span

 

[McClary's Electrical]

Re: Derate NM Cable through top plates of garage

You cannot just simply say, "no more than two" or things like that. Without konwing what these conductors are doing, you're only guessing.

I could have a hole with (4) 14/3's in it and only have 8 ccc's. The no more than two rule does not work, and should only be used if you cannot count ccc's

 

[peach]

Re: Derate NM Cable through top plates of garage

The #10 outside the wall?

An empty hole?

Bearing top plate over bored?

Nice coat hanger... wonder how those talented dry wallers are going to handle it..