The source is three phase 208/120 volt. The load consists of three single phase heaters, feed line to neutral. The three current carrying conductors and the three neutrals are in the same conduit. Assume load current is 40 amps, what size THHN conductor is required? Note: The ambient temperature is 30 degrees C. All Copper conductors.

The source is three phase 208/120 volt. The load consists of three single phase heaters, feed line to neutral. The three current carrying conductors and the three neutrals are in the same conduit. Assume load current is 40 amps, what size THHN conductor is required? Note: The ambient temperature is 30 degrees C. All Copper conductors.