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Sep 2008
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Fairmont, WV, USA
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740
Originally Posted by corbinoni
Team I ran into a question that threw me and cost me too much time to decide.Here goes.The question states:
What size PVC sleeve (24" nipple) for several NM cables is required for (3) 14/2 (2) 12/2 (1) 10/2 with the elliptical diameter of each of them,then also listed a 10/3 and a 8/3 with the regular diameter.
I found that Chap 9 Note 9 states 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.

My question is which table or tables do I use before going to Table 4 PVC 60% fill?
See Chapter 9 (70-711 in 2011 NEC) Notes (2), (4), (5), and (9).

Note (2) says if it is sleeve (not part of conduit system) then table 1 does not apply.

Note (4) says if it is a nipple (part of a complete conduit system (and 24" or less) then you can fill it to 60%.

Note (5) says if it is other than a conductor listed in Chapter 9, Table 5, you use the actual dimension.

Note (9) says if it is elliptical, use the major (largest) dimension as its diameter.

So for each cable, you were supplied its major diameter. Just as a guess let's say 14/2 has a major diameter of 1/2 inch, 12/2 5/8 inch, and 10/2 3/4 inch.

The calculated area of 14/2 would be PI*R(squared) or 3.14*(1/4*1/4) or 3.14*0.0625 or 0.196

The calculated area of 12/2 would be PI*R(squared) or 3.14*(5/16*5/16) or 3.14*0.0977 or 0.307.

The calculated area of 10/2 would be PI*R(squared) or 3.14*(3/8*3/8) or 3.14*0.141 or 0.442

3 14/2 3*0.196 or 0.588
2 12/2 2*0.307 or 0.614
1 10/2 1*0.442 or 0.442
total is 1.644 sq inches

If it is a sleeve you can fill it to 100% I guess, so according to table 4 PVC 40 the smallest conduit with that or greater diameter under the 100% column is 1-1/2 inch

If it is a nipple you can fill it to 60% so according to table 4 PVC 40 the smallest conduit with that or greater diameter under the 60% coluumn is 2 inch

2. Originally Posted by Hv&Lv
Ok, I see now... 24" is the magic length...
Not always. There is an excetption to 310.15(B)(2).
Exception: Where two different ampacities apply to adjacent portions of a circuit, the higher ampacity shall be permitted to be used beyond the point of transition, a distance equal to 3.0m (10 ft) or 10 percent of the circuit length figured at the higher ampacity, whichever is less.

3. Originally Posted by don_resqcapt19
Not always. There is an excetption to 310.15(B)(2).
Seems like a lot of people ignore that one