it's been a while since ive de-rated for conduit fill so my question is, how many 3 hot/1 neutral groups can i put in a 3/4'' pipe if the wire is #12 thhn, and on a 20 amp ckt and the terminal ratings are unknown. i am confused if it is 30a X 70%=21a or if i have to base it off of the 75 degree column. anyway i would like to put 9 #12 hots with 3 neutrals in a 3/4'' on a 20 amp ckt.