What's the sizing method for sleeving NM cables in 2" sch.40 pvc conduit ,that's 24" long going in top of a breaker panel ? Also what's the 2008 code change mean when multiple NM cable ampacities must be adjusted when passing through wood framing members that are fire or draft-stopped with caulk or sealing foam?Please give an example.
Derating NM cable
- Thread starter tdjs
- Start date
- Status
- Location
- Illinois
- Occupation
- retired electrician
The conduit fill rules do not apply to sleeves. Note that you are only permitted to install the NM in a sleeve out of the top of a surface mounted panel.
As far as the derating goes, if you install more than 4 NM cables with #12 conductors, through a hole in a wood framing member that is fire or draft stopped, you will no longer be able to protect the conductors with a 20 amp breaker. With the 5th cable you hit the 50% derating factor turning your #12s into conductors that only have an ampacity of 15 amps.
Note: As "Cow" pointed out in post #12, the conduit fill rule does apply to these sleeves.
As far as the derating goes, if you install more than 4 NM cables with #12 conductors, through a hole in a wood framing member that is fire or draft stopped, you will no longer be able to protect the conductors with a 20 amp breaker. With the 5th cable you hit the 50% derating factor turning your #12s into conductors that only have an ampacity of 15 amps.
Note: As "Cow" pointed out in post #12, the conduit fill rule does apply to these sleeves.
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quogueelectric
Senior Member
- Location
- new york
I believe if there are more than 9 current carrying conductors it has to be derated to 50%. The Idea now seems to be more smaller holes with less wire than 1 large hole with all the wires in it. I think it is easier to drill more 3/4"holes than have to find oddball breakers to connect them to.
RICK NAPIER
Senior Member
- Location
- New Jersey
Chapter nine 60% fill from table 1 notes 4,5 & 9 using the eliptical diameter of cables to figure out the area as if it were a circular cable. That is 60% of the conduits area from table 4. For 2" schedule 40 PVC it would be 1.975 square inches.
As for romexes in fire or draft stopped holes in wood framing you would derate using 310.15(B)(2)(a) an example: four 2-conductor # 12 w/ground type NM cable in a draft stopped hole woul be as follows
4 cables X 2 conductors per cable =8 current carrying conductors
Your allowed to use the 90 degree chart for derating table 310.16 and 334.80. This is 30 amps with an adjustment factor of 70% from 310.15(B)(2)(a).
30X70%=21 amps
Number 12 NM is limited to 20 amps so your OK. But if it was 5 NM cables the adjustmant factor would 50% which would limit your load an overcurrent to 15 amps.
By the time I typed this out you had plenty of responses. I quess two fingers aren't enough.
As for romexes in fire or draft stopped holes in wood framing you would derate using 310.15(B)(2)(a) an example: four 2-conductor # 12 w/ground type NM cable in a draft stopped hole woul be as follows
4 cables X 2 conductors per cable =8 current carrying conductors
Your allowed to use the 90 degree chart for derating table 310.16 and 334.80. This is 30 amps with an adjustment factor of 70% from 310.15(B)(2)(a).
30X70%=21 amps
Number 12 NM is limited to 20 amps so your OK. But if it was 5 NM cables the adjustmant factor would 50% which would limit your load an overcurrent to 15 amps.
By the time I typed this out you had plenty of responses. I quess two fingers aren't enough.
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- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
There is interesting wording in this section
So if I drill a 2" hole thru a bottom plate of a wall many feel that you must derate if more than 2 nm cables are installed in this hole. Suppose I put 12 cables in this hole and separate the cables with a piece of wood or insulation in 3 groups of 4 cables, would I then need to derate to 15 amps in Don's example? According to the wording in this section I would say no since there is spacing between the conductors. Yes? No?
Jim W in Tampa
Senior Member
- Location
- Tampa Florida
When did a M A get listed as a romex connector ?
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
????:-? huh
Jim W in Tampa
Senior Member
- Location
- Tampa Florida
male adapters are not listed for romex
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Agreed but I have seen it done many times and get inspected to boot. Not sure where the MA statement is?
Jim W in Tampa
Senior Member
- Location
- Tampa Florida
I use to do it all the time and passed. Passing does not = legal
The ul listing of the ma does not include this use.
Twoskinsoneman
Senior Member
- Location
- West Virginia, USA NEC: 2020
- Occupation
- Facility Senior Electrician
Great thread with lots of reading on bring NM into top of panel via raceway.
Lots of great opinions.
http://forums.mikeholt.com/showthread.php?t=111550
Lots of great opinions.
http://forums.mikeholt.com/showthread.php?t=111550
Cow
Senior Member
- Location
- Eastern Oregon
- Occupation
- Electrician
Does 312.5(C)Exc. (g) apply?
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Jim I agree with you. I have never done an install that way just stating my amazement that it is passed.
Jim W in Tampa
Senior Member
- Location
- Tampa Florida
Actually i have done hundreds that way and passed. Seems like easy way to protect the wires but we finally got an inspector that said NO. This is pretty much up to the ahj but if they say no then game is over cause it never was legal.
Another example of a Code Section out of touch with reality. For NM in a sleeve, I can agree with the derating after so many conductors, but this baloney about the 2" in contact thru a hole in the wood is stupid.
There is so much load diversity in most applications where multiple NM's would be run thru as hole that I am willing to bet there is NO appreciable heat buildup.
And wasn't there a thread heer some time ago where tests were conducted to see if there was any temperature rise in multiple NM's in a fire-stopped hole? I seem to reacll that there was NO appreciable heat buildup found....
There is so much load diversity in most applications where multiple NM's would be run thru as hole that I am willing to bet there is NO appreciable heat buildup.
And wasn't there a thread heer some time ago where tests were conducted to see if there was any temperature rise in multiple NM's in a fire-stopped hole? I seem to reacll that there was NO appreciable heat buildup found....
- Location
- New Jersey
- Occupation
- Journeyman Electrician
If I remember correctly that was added to the NEC because testing did find that heat buildup within the fire stopped hole exceeded the temperature limitations of the cable. IMO it's still not likely to do so in the real world.
M. D.
Senior Member
It' not ,.. this is an exception to the rule,.. if it were there would be no need for the 18 " .
http://ecmweb.com/nec/code_qa/nec_questions_answered_0201/
M. D.,
Thanks for sharing the pre-ballot proposal from 1997.
For me, this answers some long time questions I have had surrounding the exception to Section 312.5(C).
?Who would have thunk there was actually logic and reasoning, on the part of the CMP, behind the particulars of this exception
?
mweaver
Thanks for sharing the pre-ballot proposal from 1997.
For me, this answers some long time questions I have had surrounding the exception to Section 312.5(C).
?Who would have thunk there was actually logic and reasoning, on the part of the CMP, behind the particulars of this exception
?mweaver
- Status