For Canada, you should generally use 75 degree C wire column in table 2 according to rule 4-006 if the equipment is only rated for that. This is the common rating for starters, so must use 75deg C column for motors even when installing widely used 90 C wire. This is also addressed in section 28-104.
I agree with the sizing of cables using Table 2 and 5c for de-rating when installed in tray with other cables to determine de-rated copper cable ampacity. Then using 1.25 x FLA for sizing.
Example: A motor FLA of 25A x 1.25 = 31.25A and if installed in a tray with more than 14 other cables that have 3c each, you need to de-rate cable from 75degC column by 0.5 so 6AWG is 65 x 0.5 = 32.5A is adequate. This does not account for voltage drop or ambient temperature above 30C.
Anyone care to comment on this - I'd appreciate any feedback if I've overlooked something. Sizing cables this way will often be a challenge to terminate the conductors but most starters should handle the cable and with the correct compression lugs or ring terminals it should be ok at the motor too - worth a look before you pull a cable.
