I had a decision today with a electrican about conductors ampacity correct factors , we a pulling in two #18 thhn conductors for dimming control with the branch circuit conductors do have to Apply the these two dimming conductors to table 310.15B(2). Thanks
Technically speaking, if they are Class 2 or Class 3, then no derating. But if you have reclassified the dimming circuit as Class 1 to allow you to run them loose in the same raceway with power, you may have to count them. See the post relative to Class 1.