When using Table 310.15(B)(2)(a) for derating of conductors does the OCPD have to sized based on the derated value of only the current rating of conductor. For example if a #12 is derated 50% (using 90 degree C wire) 30A at 50% leaves me with 15A, my load is significantly less (around 5A) can I still connect this to a 20A OCPD or is the 15A rating also used for selection of the OCPD?