Chapter 9 Tables4&5 VS. Annex C

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ncwildcats

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Does anyone know why there is such a difference for wire fill using annex c VS. chapter 9 Tables 4&5. What I ran into is thw #12 in annex c shows 13 wires in a one inch EMT conduit. Using Chapter 9 Tables 4&5 thw #12 in a one inch EMT conduit figures out to 19 conductors. Any thoughts on this?
 
billsnuff said:
because Ch 9, Notes to Table (1) says to use Annex C for the conditions you describe..........
Click to expand...
Note (1) says "see" the annex, not "use" the annex. The
annexes are not part of the code, and not enforceable.
(see the first text in italics at the beginning of Annex C.)

It looks to me that the OP has found an anomaly in
Table C.1. THW-12 (area=0.0181 in^2) is lumped in
the same group as RHH*-12 (area = 0.0260 in^2).
RHH*-12 has ~44% more area than THW-12, so
is clearly going to fill the pipe more.

It looks like you are "safe" using the lower number in the
annex, but if there is any discrepancy, the numbers from
Chapter 9 (including application of all Table Notes) are
the correct #'s.
 
rexowner, you are correct it says see, not use, my mistake. I did look at the differences in the diameters and ran the numbers. I also looked back at chap 9 (1993 NEC) and it list the numbers of conductor as 13. still has rhw and thw lumped together. what is the *? looks like 9 cond in 1" with cover and 13 in 1" w/o the cover............what do you think?
 
billsnuff said:
rexowner, you are correct it says see, not use, my mistake. I did look at the differences in the diameters and ran the numbers. I also looked back at chap 9 (1993 NEC) and it list the numbers of conductor as 13. still has rhw and thw lumped together. what is the *? looks like 9 cond in 1" with cover and 13 in 1" w/o the cover............what do you think?
Click to expand...

billnsuff, Right, the * is without cover. my guess is that
the different insulation types were lumped together in
that part of annex c tables in order to
shorten the already very long tables in annex c, and
the numbers in the annex are on the "safe side", but
that is just a guess.
 
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