# Derate NM Cable through top plates of garage



## jar546 (Jan 10, 2010)

What IRC code would you cite?

(easy one)


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## Fortner (Jan 11, 2010)

Re: Derate NM Cable through top plates of garage

IRC 3605.4.4 or NEC 334.80


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## jar546 (Jan 11, 2010)

Re: Derate NM Cable through top plates of garage

What are these guys thinking.  Just make swiss cheese and pull 2 per hole.


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## Fortner (Jan 11, 2010)

Re: Derate NM Cable through top plates of garage



			
				jar546 said:
			
		

> What are these guys thinking.  Just make swiss cheese and pull 2 per hole.


That is what I usually see. Destroyed plates.


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## GHRoberts (Jan 25, 2010)

Re: Derate NM Cable through top plates of garage

jar546 ---

I don't want to pick on you but ...

The holes are not that bad. I would like to see them further apart, but it does not seem to be a big issue.

There is no need to derate the cables. More than 24" seems to be the "conduit" length that requires derating.


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## raider1 (Jan 25, 2010)

Re: Derate NM Cable through top plates of garage



			
				GHRoberts said:
			
		

> jar546 ---I don't want to pick on you but ...
> 
> The holes are not that bad. I would like to see them further apart, but it does not seem to be a big issue.
> 
> There is no need to derate the cables. More than 24" seems to be the "conduit" length that requires derating.


In the 2008 NEC you are required to adjust the ampacity of NM cables in accordance with 310.15(B)(2)(a). (See 334.80)

Under the 2005 NEC there was a loop hole that permitted you to not adjust the ampacity if the cables were not bundled for more than 10% or 10 feet. (See 310.15(A)(2) Exception). In the 2008 NEC 334.80 was change to state that the exception to 310.15(A)(2) would not apply to cables bundled through a firestopped framing member.

Chris


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## mtlogcabin (Jan 25, 2010)

Re: Derate NM Cable through top plates of garage



> What IRC code would you cite?(easy one)


Don't do electrical so where's the foam in the top plate penetrations

N1102.4.1 Building thermal envelope.

The building thermal envelope shall be durably sealed to limit infiltration. The sealing methods between dissimilar materials shall allow for differential expansion and contraction.  The following shall be caulked, gasketed, weatherstripped or otherwise sealed with an air barrier material, suitable film or solid material.

  1.	All joints, seams and penetrations.

  10.	Other sources of infiltration.


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## TimNY (Jan 26, 2010)

Re: Derate NM Cable through top plates of garage

Where is this located in the house?

If this were in an exterior wall of a garage that is not going to be finished, there is no concealed space, therefore no need for fireblocking.

If no fireblocking, then they are not penetrating a firestopped assembly?

I only have 2005 NEC, so I am not aware of all the verbage in the 2008, but this would seem to nullify 335.80 that raider1 quoted.


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## GHRoberts (Jan 26, 2010)

Re: Derate NM Cable through top plates of garage



			
				raider1 said:
			
		

> In the 2008 NEC you are required to adjust the ampacity of NM cables in accordance with 310.15(B)(2)(a). (See 334.80)Under the 2005 NEC there was a loop hole that permitted you to not adjust the ampacity if the cables were not bundled for more than 10% or 10 feet. (See 310.15(A)(2) Exception). In the 2008 NEC 334.80 was change to state that the exception to 310.15(A)(2) would not apply to cables bundled through a firestopped framing member.
> 
> Chris


I don't do a lot of electrical work, but my understanding is:

There is no fire stopping shown. The cables are not bundled. The breaker sizes are not specified. The usual derating from 90 degrees (wire rating) to 60 degrees (NM rating) is sufficient.

jarXXX seems to apply code requirements without enough context to make informed decisions. Perhaps jarXXX could explain how much derating the circuits need -


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## raider1 (Jan 26, 2010)

Re: Derate NM Cable through top plates of garage



> There is no fire stopping shown. The cables are not bundled.


Let me post the wording of 334.80.



> 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.


This section say "through the same opening in wood framing that is to be fire or draft stopped using thermal insulation, caulk, or sealing foam."

So IMHO the picture shows cables that run through the same opening and the building code do require that the holes in the top plate be draft stopped so adjustment of the allowable ampacity needs to be done.

Chris


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## TimNY (Jan 26, 2010)

Re: Derate NM Cable through top plates of garage



			
				raider1 said:
			
		

> > So IMHO the picture shows cables that run through the same opening and the building code do require that the holes in the top plate be draft stopped so adjustment of the allowable ampacity needs to be done.
> >
> > Chris


I agree, if it is required to be firestopped.


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## raider1 (Jan 26, 2010)

Re: Derate NM Cable through top plates of garage



			
				TimNY said:
			
		

> raider1 said:
> 
> 
> 
> ...


I agree, if it is required to be firestopped.

I would say the the top plate in the picture would need to be fireblocked in accordance with 2006 IRC section R602.8 #4.

And 2009 IRC section R302.11 #4



> R302.11 Fireblocking. In combustible construction,fireblocking shall be provided to cut off all concealed draft
> 
> openings (both vertical and horizontal) and to form an effective
> 
> ...


Chris


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## GHRoberts (Jan 26, 2010)

Re: Derate NM Cable through top plates of garage



> fireblocking shall be provided to cut off all concealed draft openings.


The pictures do not show this as a concealed area. (Perhaps jarXXX can clarify this point.)


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## jar546 (Jan 26, 2010)

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? :?


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## TimNY (Jan 27, 2010)

Re: Derate NM Cable through top plates of garage

It being a concealed location per jar's explanation, I think we're in agreement that it violated the NEC.  Get out ye old recipro saw, notch it, staple em and put a 16ga strap across the top plate.

However, I disagree that 602.8 #4 (2006) or 302.11 #4 (2009) applies if it is _not_ a concealed space.  You can't get to #4 until you've met the requirements of the section first-- namely, "In combustible construction, fireblocking shall be provided to cut off all _concealed_ draft openings"

My interpretation would be that since it is not concealed [in my theoretical scenario, not in this particular photo], you don't get to read any further and apply the subsections.  In my opinion, it would be like going to the shaft enclosure section and picking something out of there when you don't have a shaft enclosure to begin with.


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## TCN (Jan 27, 2010)

Re: Derate NM Cable through top plates of garage

I see nothing wrong here.  These cables are already derated for residential applications so much that there would have to be nine current carrying conductors before any further derating is required.  Further, IF this will be a concealed location (looks like an exterior wall, and told in the garage) the typical insulaton to be applied suffices as draft stop.


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## EPrice (Jan 27, 2010)

Re: Derate NM Cable through top plates of garage



			
				TCN said:
			
		

> ...there would have to be nine current carrying conductors before any further derating is required...


Two of the holes appear to have 10 current carrying conductors, one appears to have 12, and one 14.


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## north star (Jan 27, 2010)

Re: Derate NM Cable through top plates of garage

*TimNY,*

*The drilled holes WILL be concealed once the sheetrock is installed, so R602.8, #4 would apply.*



> 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.


*jar,*

*What's up with the lone "orange" conductor not installed in the drilled holes?   :?:*


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## Mule (Jan 27, 2010)

Re: Derate NM Cable through top plates of garage

I don't see a problem with the installation. They would need to seal the holes.

I would say the following section allows this type of installation. The conductors are only grouped together for 3" then they are seperated.

310.15 Ampacities for Conductors Rated 0–2000 Volts.

(B) Tables.

2) Adjustment Factors.

(a) 	More Than Three Current-Carrying Conductors in a Raceway or Cable. 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)(2)(a). Each current-carrying conductor of a paralleled set of conductors shall be counted as a current-carrying conductor.

You sure there's a room above? Looks like rafters going up beside the joist to me.


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## north star (Jan 27, 2010)

Re: Derate NM Cable through top plates of garage

*Mule,*

*Jeff said that this was the openings in the wall that will be located behind the ' pony wall ' above.*

*How's your recuperation going?*


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## Mule (Jan 27, 2010)

Re: Derate NM Cable through top plates of garage

Recupe going slow but getting better every day.

The Golden Years my foot!!! Titanium baby!!!!!

Thanks for asking.


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## TimNY (Jan 27, 2010)

Re: Derate NM Cable through top plates of garage



			
				north star said:
			
		

> *TimNY,*
> 
> *The drilled holes WILL be concealed once the sheetrock is installed, so R602.8, #4 would apply.*
> 
> ...


[/size][/b]

Yes, see below.



			
				TimNY said:
			
		

> It being a concealed location per jar's explanation, *I think we're in agreement that it violated the NEC*.


I agree with you..  The point was that I believe there are differing opinions as to whether or not you have to firestop the hole if it is not concealed.  We were not originally privy to the location of the penetrations, and the location made a difference to some, and not to others.



			
				TimNY said:
			
		

> My interpretation would be that since it is not concealed *[in my theoretical scenario, not in this particular photo]*


Chris and I got a bit off topic, apologies.  I tried to be clear.

Tim


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## north star (Jan 27, 2010)

Re: Derate NM Cable through top plates of garage

*TimNY,*

*No apologies are necessary!    * 

*In my own sort of "over-the-top" kind of way, I was attempting to be clear.*

*I hope that I helped in the discussion of this topic.*

*Mule, I agree, ...them thar " Golden Years ' ain't looking so golden to me*

*either.    Wishing you the very best in your recuping time.   Now, get back*

*out there and kick some code butt!    :lol:*


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## TCN (Jan 27, 2010)

Re: Derate NM Cable through top plates of garage

Looks like plenty of space to me.  They are not jammed through the typical barely big enough hole.  If they stuck a less than 24" chase in, they would be fine but the heat dissipation would be worse.  This is the concern.  Draft stop the holes appropriately and move on I say.


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## jar546 (Jan 27, 2010)

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


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## TimNY (Jan 28, 2010)

Re: Derate NM Cable through top plates of garage



			
				jar546 said:
			
		

> 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.
> 
> ...


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


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## Mule (Jan 28, 2010)

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!


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## GHRoberts (Jan 28, 2010)

Re: Derate NM Cable through top plates of garage



			
				jar546 said:
			
		

> 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.


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## Mule (Jan 28, 2010)

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.


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## raider1 (Jan 28, 2010)

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


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## north star (Jan 28, 2010)

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... *


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## GHRoberts (Jan 28, 2010)

Re: Derate NM Cable through top plates of garage



			
				Mule said:
			
		

> 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.)


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## Heaven (Feb 8, 2010)

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.


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## raider1 (Feb 9, 2010)

Re: Derate NM Cable through top plates of garage



			
				Heaven said:
			
		

> 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


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## Heaven (Feb 9, 2010)

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.


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## raider1 (Feb 9, 2010)

Re: Derate NM Cable through top plates of garage



			
				Heaven said:
			
		

> 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


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## GHRoberts (Feb 9, 2010)

Re: Derate NM Cable through top plates of garage



			
				raider1 said:
			
		

> 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.


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## Mango (Feb 9, 2010)

Re: Derate NM Cable through top plates of garage

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


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## raider1 (Feb 9, 2010)

Re: Derate NM Cable through top plates of garage



			
				Mango said:
			
		

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


So you are saying just ignore 334.80? :roll:

Chris


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## Mule (Mar 9, 2010)

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.........


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## GHRoberts (Mar 9, 2010)

Re: Derate NM Cable through top plates of garage



			
				Mule said:
			
		

> 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.)


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## Span (Mar 9, 2010)

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


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## McClary's Electrical (Mar 10, 2010)

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


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## peach (Mar 10, 2010)

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..


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