there is no place that I can use the 90 degree column to size my wire from the OCPD to the termination device
It is not as bad as that, as I said there is some equipment out there rated 90C.
The real gift of the 90C column is when we have to derate.
Lets say you are running 9 current carrying conductors in a raceway or in a bundle of cables.
310.16 lists 12 AWG at 30 amps in the 90C column which is the figure you can start with for derating.
Table 310.15(B)(2)(a) requires a 70% adjustment for that many conductors.
30 amps x .7 = 21 amps.
So now after derating you can still use these conductors for a 20 amp circuit.
If you did this derating starting at 20 amps
20 x .7 = 14 which would mean you would need to use a 15 amp breaker for these conductors.
240.4(B) is the article that allows the next standard size breaker to be used in most instances.
Oh I should mention that 14, 12 and 10 AWG are not "rated" 15, 20 and 30 amps, (they are rated higher) the requirement that we use 15, 20 and 30 amp OCPDs on these size wires is 240.4(D) which does not change the rating of the conductors just the OC protection.
[This message has been edited by iwire (edited 07-15-2003).]