6 CCC requires an 80% adj factor
Like the others, I'm not sure why you are derating. But to directly answer your question, if derating were to apply, a switch loop of less than 24" would not require derating as nipples less that 24" are exempt from derating.
the length of the run is 75 ft. Would not 10 be requred?
Why would you think 75' would be a problem? I'd wager there are multiple 75' runs in a house. With that logic, you would be upsizing almost every home run in a larger dwelling.
Won't there be 12 CCCs in the nipple?
That was my thinking. I was picturing a switch box nippled off to the side creating switch loops. Still no derating though due to less than 24".
I think Bill was just using the house as an example of some typical 12AWG branch circuits with 20A OCP. The fact that it's commercial doesn't alter the electrical properties of the wire, nor the NEC requirements for derating.
No it would not be required. To your initial question about adding a junction box and feeding the switches if your nipple length is 24" or less then no derating would need to be applied so you could use #12 AWG conductors in that nipple. Even if the nipple were longer than 24" section 310.15(A)(2)Exception may apply and derating still would not be required.
It still wouldn't matter as there is no derating required in a conduit nipple. Chap. 9 Table 1 Note 4
