Originally Posted by xlink
At one time, if I recall correctly, wires in PVC could only be used to their amperage under the 75 degree column. Then CSA decided that 90 degree conductors didn't result in temperatures above 75 degrees (Appendix B, 12-1104), so the 90 degree column was acceptable. In the 2012 code the amperages have been increased and I wonder if they forgot to reset 12-1104 to the old rule? Perhaps some NEC electricians can comment on the temperature rating of wires in PVC.
In The 2011 NEC we can have 3 current caring conductors before we need to derate the conductors and also it does not matter what type of pipe we are using.
310.15 (B) Tables. Ampacities for conductors rated 0 to 2000 volts
shall be as specified in the Allowable Ampacity Table
310.15(B)(16) through Table 310.15(B)(19), and Ampacity
Table 310.15(B)(20) and Table 310.15(B)(21) as modified by
310.15(B)(1) through (B)(7).
(3) Adjustment Factors.
(a) More Than Three Current-Carrying Conductors in a
Raceway or Cable. Where the number of current-carrying
conductors in a raceway or cable exceeds three, or where
single conductors or multiconductor cables are installed
without maintaining spacing for a continuous length longer
than 600 mm (24 in.) and are not installed in raceways, the
allowable ampacity of each conductor shall be reduced as
shown in Table 310.15(B)(3)(a). Each current-carrying conductor
of a paralleled set of conductors shall be counted as
a current-carrying conductor.
Where conductors of different systems, as provided in
300.3, are installed in a common raceway or cable, the
adjustment factors shown in Table 310.15(B)(3)(a) shall
apply only to the number of power and lighting conductors
(Articles 210, 215, 220, and 230).
Informational Note No. 1: See Annex B, Table
B.310.15(B)(2)(11), for adjustment factors for more than
three current-carrying conductors in a raceway or cable
with load diversity.