Code of the day protecting nm cable in conduit

[Jpflex]

Regarding the code of the day, the NEC book to my knowledge failed to address calculations for max conduit fill when nm cable is ran inside conduit. Obviously the nm cable sheathing takes up more space than the insulated conductors and shouldn't be calculated with only conductor diameter as typical.


However one book I came across said to measure the diameter of the nm cable jacket sheath and treat this as one conductor (percent fill table) when determining max conduit fill for nm cables. Is this correct?

 

[augie47]

The book is correct, If you are installing a cable such as NM in conduit, Table 1 Chapter 9 addresses the method used to determine fill.
If you are simply sleeving the NM to protect it from damage I know of no restriction.

 

[Jpflex]

The book is correct, If you are installing a cable such as NM in conduit, Table 1 Chapter 9 addresses the method used to determine fill.
If you are simply sleeving the NM to protect it from damage I know of no restriction.

Even if you're only using conduit to protect nm cable I do not believe you can fill it over 50 percent of conduit area for one nm cable or 40 percent for 3 or mote nm cables. I don't have code book so im going off what I recall.

 

[roger]

Even if you're only using conduit to protect nm cable I do not believe you can fill it over 50 percent of conduit area for one nm cable or 40 percent for 3 or mote nm cables. I don't have code book so im going off what I recall.

Your recollection is wrong. Even if it's a nipple less than 24" between boxes you can fill it to 60 percent.

 

[infinity]

Even if you're only using conduit to protect nm cable I do not believe you can fill it over 50 percent of conduit area for one nm cable or 40 percent for 3 or mote nm cables. I don't have code book so im going off what I recall.

Conduit fill is based on 53%-one conductor, 31%-two conductors, or 40%-three or more conductors. Chapter 9, Table 1.

 

[AC\DC]

Sleeves you can fill to your heart’s content

 

[infinity]

Sleeves you can fill to your heart’s content

I agree. Take a length of conduit and put a box on both ends and you have a raceway. Put a box only on one end and you have a sleeve. Given the minutia of the NEC I'm surprised they haven't dropped the hammer on what a sleeve is.

 

[Rick 0920]

You also don't want to overlook Art. 312.5 (C) Chap, 9 Table 1 Note 9 states that multi-conductor cables count as one conductor so the 53% fill is applicable.

 

[Rick 0920]

Sleeves you can fill to your heart’s content

Look at 312.5 (C) ex. There are certain things that you must do.

 

[gene6]

Look at 312.5 (C) ex. There are certain things that you must do.

it should be emphasized there are exactly two types of conduit sleeves, a sleeve that attaches to a panel and all others.
The 312.5(C) applies to sleeves that attach to panels, meters and or 'cabinets and cut out boxes'.
the second type is all others, like a isolated sleeve or a sleeve that hits a Jbox, for those per Note 2 in the tables in chapter 9:

(2) Table 1 applies only to complete conduit or tubing systems
and is not intended to apply to sections of conduit or tubing
used to protect exposed wiring from physical damage.

working for a company that does a lot of residential panel changes I got to say the '312.5(C) exception' sleeves have caused more inspection failures and debates about code with inspection agencies than any other code section.
In the '312.5(C) Exception Item (7) was changed in the 2017 to add Note 2 to the tables
in Chapter 9 does not apply to this condition;

(7) Where installed as conduit or tubing, the cable fill does not
exceed the amount that would be permitted for complete
conduit or tubing systems by Table 1 of Chapter 9 of this
Code and all applicable notes thereto. Note 2 to the tables
in Chapter 9 does not apply to this condition.

A job I recently looked at was a new exterior panel mounted on a structure, they wanted some new circuits but no exposed conduit, I opened it up and that is when I found this had a 2" PVC male adapter going out the back of the panel into a wall space, then all the romex and even old BX come thru this 'sleeve' into the loadcenter. Its a very narrow style 40 circuit loadcenter made by Eaton, with 1/2 the space on the left taken up by the meter, and there would be no possible way to have 40 circuits enter this loadcenter and each one be secured to the panel per 312.5(C). Its like they intended it to only feed a few raceways with many circuits in each raceway, but no residences here have raceway, all are NM or old BX cable.

 

[wwhitney]

As per the previous post, 312.5(C) is an issue for sleeves only if you want to skip attaching each cable to the cabinet.

But if you can figure out a way to attach each cable to the cabinet, the 312.5(C) is satisfied. For example, you could install a "ground bar" perpendicular the sleeve, crossing in front of the sleeve opening. Then pull all the screws out of the ground bar lugs and cable tie each cable to one of the lug openings as the cable passes over it. The cable sheath would stay intact until after the cable tie. Would obviously require adequate space within the cabinet.

Cheers, Wayne