Example to ponder:
Hall with 12 light fixtures, each controlled by its own switch. All switches are located in a single (very ugly) multigang box, all fixtures are fed from a single raceway. Each fixture has a ballast rated at 1.3A. All fixtures are supplied by a single 20A circuit. The raceway from the switch box to the first fixture is carrying a total of 14 conductors: 12 switched 'hot', 1 grounded, 1 equipment ground.
For purposes of derating, how many current carrying conductors are considered to be in the raceway, and is 12ga THHN suitable for this install?
If we assume single phase service 240V/120, and replace the above install with a multiwire circuit, where 6 of the switches are supplied by one supply leg, 6 by the other supply leg, with a single shared neutral, does the 'official' number of current carrying conductors go up or down?
In this latter case, is the more or less chance of overheating the conductors?
-Jon
