NM can be run in conduit. It is considered to be a single wire with diameter based on its greatest elliptical measurement. If there are more than 2 cables the maximum FILL is 40%. If you exceed the FILL you cannot remedy the situation by derating--you need to pull some wires out. As for derating, I assume that NM would be treated like wire, 4 wires are derated by .8 but I cannot find this in the Code.. Also what is NM #12 rated for ampacity? Is it 30 amps because it is THHN? Or 25 amps because it is 60 degrees? 25 x .8 = 20 (So even after derating by .8 you could use a 20 amp breaker.) Or is NM #12 limited to 20 amps because it is NM...... Also, I thought BUNDLING applies to wires that are embedded in insulation.
Little Romex Question
- Thread starter George Stolz
- Start date
- Status
- Location
- Windsor, CO NEC: 2017
- Occupation
- Hospital Master Electrician
George Stolz said:
Well, check this PDF out, and look on the second page below the table. Also, check out exception 5 to 310.15(B)(2). If MC cables on bridle rings are considered bundled, then there is reason to assume that NM cable routed through holes every 16" are subject to the same interpretation.
4 cables = 8 conductors = 70% (Table 310.15(B)(2)(a))
It is not THHN. The conductors inside NM are mystery meat.
See 334.80. We can use the 90? column for our starting point for derating.
There does not need to be insulation to begin worrying about bundling.
- Location
- Windsor, CO NEC: 2017
- Occupation
- Hospital Master Electrician
The pipe sleeve is not really part of my question, it's an old picture of an old problem. I didn't want anybody to think I had 5 holes in each TGI. But if the conversation follows that tangent I won't object.
Thanks!
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
You may see installations that have excess "bundled" cables and have been that way for years with no apparent problems. Load diversity contributes to the amount of heat that is actually produced.
In most dwellings outside of a few loads like HVAC loads, most circuits are not loaded at high levels for long periods of time. NEC does not allow us to consider this however because there is no real way to tell what the load will be like on general purpose type circuits and even lighting circuits in dwellings are not as predictable as they are in a commercial setting.
In most dwellings outside of a few loads like HVAC loads, most circuits are not loaded at high levels for long periods of time. NEC does not allow us to consider this however because there is no real way to tell what the load will be like on general purpose type circuits and even lighting circuits in dwellings are not as predictable as they are in a commercial setting.
The pipe sleeve is not really part of my question, it's an old picture of an old problem. I didn't want anybody to think I had 5 holes in each TGI. But if the conversation follows that tangent I won't object.
Thanks!
if the pipe sleeve is caulked, sealed, fire stopped or draft stopped, then it disallows the 90 degree column for the purpose of derating and changes the the values. read 2nd paragraph of 334.80 with particular attention to the last two lines (....and the provisions of 310.15(A)(2), Exception, shall not apply).
jetlag
Senior Member
- Location
- Eatonton, Georgia
NM contains thw conductors but there is a code that says it must be counted as 60 deg wire because of the seath cable . Even then the 25 amp rating gives room to take care of minor derating on a 20 amp breaker. There have been a lot of post as to why we dont have to derate nm in a hot attic and its seems the extra 5 amp is usually enough.
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310.15(A)(2) exception has nothing to do with the 90 degree column for the purpose of derating. If I have a circuit where only a short portion of it is bundled (< 10 ft. and < 10% of the circuit length), the exception allows me to use the ampacity of the non-bundled portion of the circuit rather than the ampacity of the bundled section. 334.80 prohibits me from using that exception when running through an insulated etc. hole, so I have to use the bundled ampacity regardless of how short the section is that runs through an insulated hole. This does not prohibit me from starting my deration from the 90 degree column.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
This is totally inaccurate. NM contans 90C wire and that is all we know since the manufacturers can use whatever they want and it is not labeled.
The 60C is not because of the sheath but rather the application and you may use 90C to derate from as long as it is not over the 60C rating in the end.
Dennis could you look at my post (#25) and explain the 310.15(A)(2) exception as it applies to section 334.80 where it states 'and the provisions of 310.15(A)(2) shall not apply'
jetlag
Senior Member
- Location
- Eatonton, Georgia
Well i think totally inacurate is a little harsh of you, the 60 degree max rating is what is important to remember you would have to do serious derating to get the 90 wire below 60 degree rating. You say the sheath is not the reason but you didnt give one, thats what an instructor at the college for license class has been teaching for years
jetlag
Senior Member
- Location
- Eatonton, Georgia
What is the code that says you can start to derate nm at 90 deg because the manufacturer says its 90 deg , the wire is not marked in a sheath cable thats why the derate must start with the lowest 60 deg
CONSTRUCTION
Southwire's Romex SIMpull ? Type NM-B cable is manufactured as 2, 3, or 4 conductor cable, with a ground wire. Copper
conductors are annealed (soft) copper. Stranded conductors are compressed stranded. Conductor insulation is 90?C-rated
polyvinyl chloride (PVC), nylon jacketed. Southwire's SIMpull ? Designed for Easier Pulling, Resulting in Easier installation.
The cable jacket is color-coded for quick size identification; White - 14 AWG, Yellow - 12 AWG, Orange - 10 AWG, and Black -
8 AWG and 6 AWG.
The above is from the product specification from Southwire as it relates to their "romex".
110.14(C) - 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.
Pete
Southwire's Romex SIMpull ? Type NM-B cable is manufactured as 2, 3, or 4 conductor cable, with a ground wire. Copper
conductors are annealed (soft) copper. Stranded conductors are compressed stranded. Conductor insulation is 90?C-rated
polyvinyl chloride (PVC), nylon jacketed. Southwire's SIMpull ? Designed for Easier Pulling, Resulting in Easier installation.
The cable jacket is color-coded for quick size identification; White - 14 AWG, Yellow - 12 AWG, Orange - 10 AWG, and Black -
8 AWG and 6 AWG.
The above is from the product specification from Southwire as it relates to their "romex".
110.14(C) - 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.
Pete
jetlag
Senior Member
- Location
- Eatonton, Georgia
Never mind I see it now , 334.80
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
It was harsh- I apologize- didn't mean it to be harsh. I spoke with the manufacturers of nm cable and they assured me the insulation on the jacket was the same as the wire- 90C.
I guess I was responding to the jacket info, the insulation info being inaccurate. I have heard the theory of the jacket being 60C but have learned it to be untrue.
I am not sure why nm is limited to 60C but that you are correct.
You also added that 25 amps would be used for derating when we can use 30amps. So not totally inaccurate but incorrect on 3 points.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
That's correct. This was added in the 2008 NEC because the derating requirement for caulked/fire-stopped holes added in the 2005 was mostly unenforceable due to the exception in 310.15(A)(2).
- Location
- Massachusetts
I agree 100%.
jetlag
Senior Member
- Location
- Eatonton, Georgia
Yea and this caused me a big problem , i have been doing service calls the last few years and not wired a whole house since the 2008 code . Well I was getting ready to wire a house in 09 and the inspector was out and said only 2 wires allowed in a hole, I was trying to think what he meant and he went on to something else . So I started a thread on here to aks why he said that and all the replies came back what I allready knew , the derate for bundle doesnt even start till 5 or more nm . Well I just found out to late he must have been talking about the fire chaulked holes which is enforced in the 08 code. My next question is why did he say 2 cables the chart for that shows the same derate for 2 and 3 cables or 4 and 6 current carrying conductors. in fact 7-9 conductors is still only 70 % x 30a = 21a where is the inspector getting 2 wires in hole I had to pull some out with the chaulking already in.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
He said 2 cables because he didn't understand how to properly apply derating to the NM cables in the caulked hole. You can put up to 9 CCC's in that hole before it will effectively change the ampacity of #14 or #12 conductors. That's up to 4-14/3 or 4-12/3 cables in one hole with the caulking.
- Location
- Windsor, CO NEC: 2017
- Occupation
- Hospital Master Electrician
He apparently was not informed about the specifics of the code. If you had less than 9 CCC's in a bundle, or in an insulated hole, then you were still compliant after derating.
- Location
- Windsor, CO NEC: 2017
- Occupation
- Hospital Master Electrician
Sometimes the most firmly held lessons were dealt harshly. I think Dennis' post was spot on - sometimes the truth should be dispensed directly to get a point across.
Then someone should invite that instructor to the forum, so we can straighten him out too. Some of the most heated debates around here are with instructors with a bad concept locked into their heads. IMO, they are the best discussions, because as long as they can keep an open mind, their teachings improve.
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