NM cable in caulked holes

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DaveBowden

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St Petersburg FL
Trying to understand 334.80 and I have a question. First (and probably most importantly) is the neutral counted as a current carrying conductor? I think 310.15(B)(4)(a) says no. If its not, does that mean we can install as many 2 wire cables in a hole as we want without derating? Can we add two 3 wire cables into that hole too?
 
You need to count up the CCC's in the hole and derate according to 310.15(B)(2)(a). For neutral conductors you need to look at 310.15(B)(4) to determine if the neutral is a CCC.
 
That's pretty much my point for the neutral. I don't think it needs to be counted in a single phase application.
334.80 says more than two cables containing two or more CCC. A 2 wire NM cable has only one CCC if the neutral isn't counted.
 
If your installing NM I would think it's reidential and you are installing general lighting BC . Further assuminging you are using two wire for 120V outlets then it's a pretty good bet the white conductor is current csarring and not just handeling unbalanced current.

see
310 15 (B)(4) Neutral Conductor.
(a) A neutral conductor that carries only the unbalanced current from other conductors of the same circuit shall not be required to be counted when applying the provisions of 310.15(B)(2)(a).

If you have two or more two wire(meaning two current carrying).

I wounld suggest you derate. The good news is NM-B is 90 degree and by the time you get to the final corrected ampacity you may not need to increase the condctor size
 
cpal said:
If your installing NM I would think it's reidential and you are installing general lighting BC . Further assuminging you are using two wire for 120V outlets then it's a pretty good bet the white conductor is current csarring and not just handeling unbalanced current.

see
310 15 (B)(4) Neutral Conductor.
(a) A neutral conductor that carries only the unbalanced current from other conductors of the same circuit shall not be required to be counted when applying the provisions of 310.15(B)(2)(a).

If you have two or more two wire(meaning two current carrying).

I wounld suggest you derate. The good news is NM-B is 90 degree and by the time you get to the final corrected ampacity you may not need to increase the condctor size
Click to expand...

The 90 degree rating can only apply as derating purposes. Standard rating for this type of cable (romex) is 90 degree.
 
DaveBowden said:
That's pretty much my point for the neutral. I don't think it needs to be counted in a single phase application.
334.80 says more than two cables containing two or more CCC. A 2 wire NM cable has only one CCC if the neutral isn't counted.
Click to expand...



Give me one instance where this is true. I'd like to hear it. I disagree. A 14/2,,,12/2,,,on single phase single pole breaker has 2 ccc's
 
kacper said:
The 90 degree rating can only apply as derating purposes. Standard rating for this type of cable (romex) is 90 degree.
Click to expand...

The OP was quoting 334.80 in the post I never mentioned that you could load beyound the 60 deg col. But thanks for the clarification.
 
In a two wire NM cable, the neutral IS current carrying. For power to flow, both would carry the same current so the neutral IS current carrying. (The only time is is not in when it is only carrying the unbalanced load).
The same Code section (338.40) that requires you to derate for caulked holes notes that NM is a 90? rated conductor. So, for derating purposes, #12 NM would have a 30 amp ampacity so you would not encounter a problem until you had over 9 current carrying conductors (310.15)(b)(2)(a).
(4) 12-2 NM would have an ampacity of 21 amps so no derating problem.
 
thanks for the answers. We just adopted the 2008 code and its been over a year and a half since my Cont. Ed. class on the changes. Trying not to miss anything on my estimates.
 
Deciding if the neutral is or isn't current carrying can be tricky. For example a 3-wire MWBC fed from a 120/240 volt system would only contain 2 CCC's. Use that same MWBC on a 208Y/120 volt system and you have 3 CCC's. For a hole that is caulked in a dwelling, with a 120/240 volt supply, you could actually put 4-12/3 cables in through the hole before derating would have any affect on the 20 amp ampacity of those cables since it would still be only 8 CCC's.
 
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