# Number of NM cables allowed in single opening?



## Darren Emery (Mar 26, 2012)

Anyone have a problem with the large number of conductors through the single knockout? If so - code section from IRC would be great.Sorry for the poor pic - still carry a dumb phone.

View attachment 1673


View attachment 1673


/monthly_2012_03/572953e5aa88c_ResPanel.jpg.17f950a65f5e6cececd3024ad923f02b.jpg


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## steveray (Mar 26, 2012)

Top plate penetrations that are fireblocked, I think it's about 9 current carrying conductors before we have to worry about derating.....in that pic, the bundling for that distance looks like cause for concern as well...Is the connector they used listed for a particular max number of cables? That is where I would start....


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## codeworks (Mar 26, 2012)

i see that crap here, all the time, and am working on getting it changed. (retraining electricians who never developed good habits on rough in, or were never taught correctly)  derating factors come into play (over 2) see 334.80 of the NEC 2008. these specifics are not covered in the irc, but arer in nec, irc code is based out of nec, yadda , yadda, yada. unless connector is listed for all of those conductors, it is non compliant. you are on the right track


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## north star (Mar 26, 2012)

*+ + +*

Also, refer to Section E3605.2 [ `06 IRC ].

*+ + +*


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## Dennis (Mar 26, 2012)

I don't know about the IRC but the NEC would be more concerned where the wires penetrate the top plate with fire caulk.  I would also bet that the NM connector is not rated for that many cables. Generally they are rated for 2 cables at most.

The number of CCC is 9 max.  Once you get to 10 CCC then you must derate 50%.  You should know that not all conductors are necessarily CCC.  I can elaborate if needed.


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## north star (Mar 26, 2012)

*= = = =*

Dennis,

Yes kind sir, ...please DO elaborate!.......Code sections; from the IRC

& NEC are especially helpful to me!

= = = =


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## gbhammer (Mar 26, 2012)

Dennis said:
			
		

> The number of CCC is 9 max.  Once you get to 10 CCC then you must derate 50%.  You should know that not all conductors are necessarily CCC.  I can elaborate if needed.


   That would be greatopcorn


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## Dennis (Mar 26, 2012)

I don't have the IRC. So NEC is what I will go with.  I believe I posted this before in another thread.  Article 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).*


So table 310.15(B)(2)(a) 2008 NEC-- the numbers are different in the 2011--T. 310.15(B)(3)(a)--- is a derating table.  It states that 7-9 CCC must be derated at 70%.  If we go to Table 310.16 and use #12 as an example  we see that #12 at 90C is rated 30 amps.  70% of 30 = 21 amps so a 20 amp breaker will work.  Even though NM is rated at 60C based on the art. shown above we are still allowed to use 90C for derating as long as the final overcurrent device is not higher than the weakest link.  The lugs are 75C but NM is rated 60C so that is out weakest link.

Now how can we tell if a wire is a CCC.  If it is 2 wire nm then you will have 2 CCC.  However in a single phase setup generally speaking if you share the neutral with 2 hot conductors on opposite phases then the neutral does not carry current.  It will carry current if the circuit is all computer equipment or fluorescent lighting.  Look at 310.15(B)(4).   Now if you have a 3 phase system and a shared neutral with just 2 phases then the neutral counts as a CCC, however if it is shared with all 3 phases then the neutral doesn't count.

Does this help?


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## Dennis (Mar 26, 2012)

To better understand this I made a very simple google docs spreadsheet.  Type in 20 amps in all three phases and see what the neutral current is.  Play with different numbers.  The neutral carries current but the total of the wires will never be larger than the max amp of the 3 phases.

Click Here.  This should work online.  You can also download it if you want.


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## north star (Mar 26, 2012)

*= = = = **>*

Dennis,

Thanks for the input!.........Sooooo, essentially, ...in the submitted

picture, they are going to have to remove that grouping of CCC's

and install them "unbundled".......Typically, the electrician will not

want to derate anything once the inspector notifies him of the

discrepancies.

Good training picture Darren Emery!........Not very clear, but a

good training opportunity none-the-less! 

*<** = = = =*


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## Dennis (Mar 26, 2012)

north star said:
			
		

> *= = = = **>*Dennis,
> 
> Thanks for the input!.........Sooooo, essentially, ...in the submitted
> 
> ...


You're welcome.  It is hard to tell how many CCC there are in that bundle but it does appear to be more than 9.  The connector is a NO-NO also.


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## Dennis (Mar 26, 2012)

BTW.  I don't think you have to derate because of the connector but because of the wire going thru a fire caulked top plate.  If the wires are bundled like that for more than 2' than you would also need to derate so without more of the photo I cannot say for sure.


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## Dennis (Mar 26, 2012)

I guess I should give you the art. where you are allowed to derate from the 90C.  art.110.14©



> © Temperature Limitations. The temperature rating associated with the ampacity of a conductor shall be selected and coordinated so as not to exceed the lowest temperature rating of any connected termination, conductor, or device. *Conductors with temperature ratings higher than specified for terminations shall be permitted to be used for ampacity adjustment, correction, or both.*





> All new equipment is pretty much rated at 75C.  Older panels may be 60C.  If there is no label on the panel or the lugs then we should assume 60C for 100 amps and lower  and 75C for over 100 amps.  110.14©(1)-- also wire size may be considered.(1) Equipment Provisions. The determination of termination provisions of equipment shall be based on 110.14©(1)(a) or ©(1)(b). Unless the equipment is listed and marked otherwise, conductor ampacities used in determining equipment termination provisions shall be based on Table 310.16 as appropriately modified by 310.15(B)(6).
> 
> (a) 	Termination provisions of equipment for circuits rated 100 amperes or less, or marked for 14 AWG through 1 AWG conductors, shall be used only for one of the following:
> 
> ...


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## Dennis (Mar 26, 2012)

I feel like a thread hog but I keep finding more info.  Check out this youtube video by Mike Holt- you can click on the arrow and it should work.  It is a bit slow moving but it gets the point of derating and temp. limitations down well.

[video=youtube;WL81zOzNagM]


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## ICE (Mar 26, 2012)

Dennis,

Your last post would be a good one for the useful links forum.


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## Dennis (Mar 27, 2012)

I put it in the useful links.

BTW, here is a useful graphic that shows the temperature rating of terminals.  Most do not know this - nor did I until recently.  I believe this will be on the newer lugs.


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## Dennis (Mar 27, 2012)

One More.  The neutrals would be a violation of art. 408.41


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## north star (Mar 28, 2012)

*= $ =*

Dennis,

Thank you for the input!......Excellent graphics and [ code based ] explanations!

*= $ =*


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