stew said:i am assuming by your terminology of 2 ys you mean 2 full boats in which case you have 6 conductors. the conductors then must be derated per 310.15(B)(2)a. to derate when using thhn start with the 90 degree rating of the conductor which is 30 amps, derate at 80% to 24 amps and there you are. 20 amp breaker is just fine.
rybrama said:on a 4 wire 208/120 v 3 phase wye, if pulling 2 wyes of # 12 thhn stranded for receptacles and flourescent lighting, is the 90degree C rating of 12 thhn to be used or the 75 degree rating of the receptacle terminal