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#206304 - 06/15/12 08:27 AM type NM in conduit
jkraft Offline
Member

Registered: 05/05/03
Posts: 75
Hello,
Can someone direct me to the NEC section regarding sleeveing romex in conduit for a combination of 12/2 and 14/2, over 10'
thanks,
Joe

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#206307 - 06/15/12 09:14 AM Re: type NM in conduit [Re: jkraft]
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9045
Loc: Estero,Fl,usa
334.15(B)
Quote:
Protection from Physical Damage. Cable shall be protected from physical damage where necessary by rigid metal conduit, intermediate metal conduit, electrical metallic tubing, Schedule 80 PVC conduit, or other approved means. Where passing through a floor, the cable shall be enclosed in rigid metal conduit, intermediate metal conduit, electrical metallic tubing, Schedule 80 PVC conduit, or other approved means extending at least 150 mm (6 in.) above the floor.


Note 9 to table 9 (conduit fill) says
Quote:
(9)A multiconductor cable or flexible cord of two or more conductors shall be treated as a single conductor for calculating percentage conduit fill area. For cables that have elliptical cross sections, the cross-sectional area calculation shall be based on using the major diameter of the ellipse as a circle diameter.


two cables can't be stacked and measured, You have to compute for "2 conductors" the size of the widest dimension so you end up with some pretty big pipe.
I haven't run the numbers on a 12 and a 14 but 1" would not surprise me
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Greg Fretwell

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#206308 - 06/15/12 09:41 AM Re: type NM in conduit [Re: gfretwell]
jkraft Offline
Member

Registered: 05/05/03
Posts: 75
thanks for your help Greg, looking at those sections now and trying to determine what size IMC would be needed for 1-12/2 and 2-14/2???

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#206309 - 06/15/12 11:03 AM Re: type NM in conduit [Re: jkraft]
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9045
Loc: Estero,Fl,usa
OK lets run the numbers
I will use commie metric because I prefer decimals

The 14ga I have measures 9mm, 12ga measures 10mm (across the widest part.

The area is the radius (half the diameter above)squared times pi (3.14)

5 x 5 x 3.14 = 78.5 mm2
4.5 x 4.5 x 3.14 = 63.6 mm2
Total cable area = 142.1 mm2

Take that to table 9 IMC "2 wire" column and you end up with 1" IMC (up to 192 mm2)
3/4 only gives you 117 mm2

See why I wasn't surprised? wink

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Greg Fretwell

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#206316 - 06/15/12 06:59 PM Re: type NM in conduit [Re: jkraft]
George Little Offline
Member

Registered: 01/18/04
Posts: 1492
Loc: Michigan USA
Nice answer Greg. Not everyone knows about this approach. Most contractors want to skin the outer jacket from the NM cable and not worry about the rules. A clear violation of 312.5(C)(e).


Edited by George Little (06/15/12 07:12 PM)
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George Little

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#206317 - 06/15/12 08:27 PM Re: type NM in conduit [Re: jkraft]
HotLine1 Offline

Member

Registered: 04/03/02
Posts: 6804
Loc: Brick, NJ USA
Greg:
Ditto with what George said! Nice!!
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John

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