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type NM in conduit #206304 06/15/12 11:27 AM
Joined: May 2003
Posts: 74
J
jkraft Offline OP
Member
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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Re: type NM in conduit [Re: jkraft] #206307 06/15/12 12:14 PM
Joined: Jul 2004
Posts: 9,409
G
gfretwell Online Content
Member
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


Greg Fretwell
Re: type NM in conduit [Re: gfretwell] #206308 06/15/12 12:41 PM
Joined: May 2003
Posts: 74
J
jkraft Offline OP
Member
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???

Re: type NM in conduit [Re: jkraft] #206309 06/15/12 02:03 PM
Joined: Jul 2004
Posts: 9,409
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gfretwell Online Content
Member
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



Greg Fretwell
Re: type NM in conduit [Re: jkraft] #206316 06/15/12 09:59 PM
Joined: Jan 2004
Posts: 1,498
G
George Little Offline
Member
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).

Last edited by George Little; 06/15/12 10:12 PM.

George Little
Re: type NM in conduit [Re: jkraft] #206317 06/15/12 11:27 PM
Joined: Apr 2002
Posts: 7,121
HotLine1 Online Content
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Greg:
Ditto with what George said! Nice!!


John

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