Hi,
   My school has 2X4 parabolic recessed flourescent troffer lights that hold 3 tubes, and I have a question about how they are wired.  Each room has 2 switches, when you turn one on, just the middle bulb in each fixture turns on.  When you turn on the other switch, it turns on the outside 2 bulbs. My question is, how do you wire a fixture up to operate like this?  Also is there just one ballast in set ups like this or does it require 2?

It has 2 ballasts, one ballast wired to one switch and other ballast wired to the other switch....so one ballast is for one lamp and other if for 2 lamps......I have been to schools and places that were wired like that.

I wired up these same fixtures at my work...yes, there are two ballasts. One for the middle bulb, and one for the outer ones. It has special multi-pin quick-connects that links all the fixtures together....there are two hot wires, one for each ballast in the connecting power cable. All the middle lamp ballasts connect to the red wire and all the outer lamp ballasts connect to the black  wire.

I wired one up the same way but it was a 4 lamp fixture but i used 2 of the 2 lamp ballast's. Ballast 1 controlled lamp 1 and 4 and ballast 2 controled 2 and 3.

I like the way some buildings do that. It's 3 level dimming without any expensive ballasts!