Changing ballasts in a strip mall today, there was a 347V HO ballast working a single lamp fixture that was burned out. I opened it up, and to my surpise, it was a 2 lamp ballast. The red leads connected to one end of the lampholder, the blue leads connected to the other end of the lampholder. The yellows (common) was capped. I've never seen such an installation before, yet when I replaced the ballast, the single lamp worked fine again. Is it common to wire single tubes this way? I've never seen it, and the wiring diagram and info on all the 2 lamp ballasts I've ever seen relates to 2 tube setup.