NM cable in conduit

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jetlag

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Hi , I know it is in the NEC that you can't use NM cable installed in conduit as a "Wiring Method" . It can be ran in conduit for protection from physical damage , like up a masonry wall in an unfinished basement or in a conduit sleeve passing through a masonry wall . Can somene find that in the NEC for me . I have been looking but can't remember what code that is . I need to show it to some one that does not believe me . Thanks
 
It's not prohibited, but you are supposed to size the conduit as if it was a round conductor the same size as the larger dimension.
 
NM can be run in complete raceways just like single conductors. The fill has to comply with Chapter 9, Note #9.

(9) A multiconductor cable, optical fiber cable, or flexible cord of two or more conductors shall be treated as a
single conductor for calculating percentage conduit or tubing 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. Assemblies of single insulated conductors without an overall covering shall not be considered
a cable when determining conduit or tubing fill area. The conduit or tubing fill for the assemblies shall be
calculated based upon the individual conductors.
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There is even a requirement that it be in a raceway where installed in a building that is required to be of Type I or II construction. 334.10(5). Not sure why anyone would want to do that...if you have to install the raceway, you might as well use single conductors in the raceway.
 
Thanks for replies , i remember that you have to count the major diameter of a cable as if that was the diameter of a round cable . I have never checked but I believe one 12/2 w/g NM cable would exceed the conduit fill for 1/2 " EMT . I'm going to check on using NM cable in conduit not being allowed as a complete wiring method . It could have been in one of the older code books from the 90"s .
 
jetlag said:
Thanks for replies , i remember that you have to count the major diameter of a cable as if that was the diameter of a round cable . I have never checked but I believe one 12/2 w/g NM cable would exceed the conduit fill for 1/2 " EMT . I'm going to check on using NM cable in conduit not being allowed as a complete wiring method . It could have been in one of the older code books from the 90"s .
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You won't find it in any code year. What you might be thinking of is NM isn't allowed in conduit outside. That's because the inside of conduit installed outdoors is considered a wet location and NM isn't allowed in a wet location. This just changed a few cycles ago.
 
Little Bill said:
You won't find it in any code year. What you might be thinking of is NM isn't allowed in conduit outside. That's because the inside of conduit installed outdoors is considered a wet location and NM isn't allowed in a wet location. This just changed a few cycles ago.
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Thanks Little Bill , That's a big help . I think the reason I remembered that wrong is because you have to go to larger conduit to get the same number of conductors you would with single strand wire because of the conduit fill , No one would want to design a special conduit system just so they could install romex in it .
 
Little Bill said:
You won't find it in any code year. What you might be thinking of is NM isn't allowed in conduit outside. That's because the inside of conduit installed outdoors is considered a wet location and NM isn't allowed in a wet location. This just changed a few cycles ago.
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Thanks Little Bill , could you give me the the NEC code number for NM not allowed in conduit outside . Thanks
 
Start with the article 100 definition of Location, Wet, then see 300.9, and 334.10

Roger
 
jetlag said:
Thanks Little Bill , That's a big help . I think the reason I remembered that wrong is because you have to go to larger conduit to get the same number of conductors you would with single strand wire because of the conduit fill , No one would want to design a special conduit system just so they could install romex in it .
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Actually you are allowed more fill with a single conductor than you are with multiple conductors take a look at the tables in chapter 9, 1 wire 53%, two wires 31%, over 2 wires 40%, and 60% for 24 inch or less nipples.

There is no fill requirements when using raceway as a protective sleeve though.

NM doesn't exactly have same dimensions from one manufacturer to another or over time has changed within same manufacturer as well.
 
jetlag said:
Thanks Little Bill , could you give me the the NEC code number for NM not allowed in conduit outside . Thanks
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"Inside a conduit" is not a location. Conductors in a conduit are located wherever the conduit is located.
 
LarryFine said:
"Inside a conduit" is not a location. Conductors in a conduit are located wherever the conduit is located.
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Well "splain" this then.......

300.9 Raceways in Wet Locations Above grade. Where raceways
are installed in wet locations above grade, the interior of
these raceways shall be considered to be a wet location. Insulated
conductors and cables installed in raceways in wet locations
above grade shall comply with 310.10(C).
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Little Bill said:
Well "splain" this then.......
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That was added to make it clear that where the raceway is in a wet location, wet location wiring methods are required i the raceway. A number of code users were saying that as long as the cable or conductors are in the raceway, they are in a dry location, even if the raceway itself is in a wet location. The change just make it clear that the inside of the raceway is "considered" to be a wet location.
 
LarryFine said:
I meant that the inside of the conduit is in the same location the outside of it is.

If you want to call the interior a "location", that's fine; just call it a "wet location".
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That's what I called it, "wet location" and I just quoted what the code said. I don't recall saying just "location".
 
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