2017 NEC Update on "Plexing" individual conductors and 54% Fill

[MasterTheNEC]

Greetings Folks,

As man of you may already know, last year their was a good topic (since closed) on what constitutes a "cable" and if "plexing" of conductors (pre-cabling) them at the factory made a difference. You know, twisting cables and no outer sheathing and saying that this can meet the allowance in Chapter 9, Table 1, Note 9 for the 53% fill.

We as you know I always disagreed and said you could not use the 53% fill.......that they had to be at 40% fill ( over 2 conductors of course). Finally the 2017 NEC clears up the confusion and it's original intent. ( in my opinion).

"(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."

So in terms of the raceway fill argument, it appears CMP 8 has spoken.

 

[infinity]

Makes sense to me. If I strip of the jacket of an MC cable and put it in a raceway the 40% fill would apply.

 

[wwhitney]

For equal sized conductors, I think that the only time you'd come out ahead if you could plex them and count them as one cable for a 53% fill would be if you could make a complete hexagonal packing of 7 or 19 conductors. Then the packing density within the overall bounding circle would be 7/9 = 77.8% or 19/25 = 76%, both of which exceed 40/53 = 75.5%.

For 3 equal sized conductors, for example, the packing density is only 3 / (1+2/sqrt(3))^2 = 64.6%.

So the change to the wording is basically academic.

Cheers, Wayne

 

[MasterTheNEC]

For equal sized conductors, I think that the only time you'd come out ahead if you could plex them and count them as one cable for a 53% fill would be if you could make a complete hexagonal packing of 7 or 19 conductors. Then the packing density within the overall bounding circle would be 7/9 = 77.8% or 19/25 = 76%, both of which exceed 40/53 = 75.5%.

For 3 equal sized conductors, for example, the packing density is only 3 / (1+2/sqrt(3))^2 = 64.6%.

So the change to the wording is basically academic.

Cheers, Wayne

However, in many cases it was the basis for a entire "Marketing Campaign" and it should not have been. Just happy it is written in Blood...I mean Code now.