CJS,
You cannot pull 9 #12's in a conduit without derating! I certainly never would and I couldn't get away with it around here either!
Correct, but the derating doesn't change anything. Table 310.16(B)(2)(a) requires a 70% adjustment factor for 7 to 9 current carrying conductors in a raceway or cable. The ampacity of #14 THHN is 25 amps and #12 is 30 amps. The adjusted ampacities for these conductors with 9 current carrying conductors in a race way is 17.5 amps for the #14 and 21 amps for the #12. The maximum permitted overcurrent protection per 240.4(D) is 15 amps for the #14 and 20 amps for #12, so for all practical purposes, there is no derating under these conditions.
As far as using conduit, I see no real advantage of PVC over NM, but I believe that the use of EMT is a safety improvement over both PVC and NM.
Don
