On NPF F30T8 ballasts, is it detrimental to run an F30T12? I’ve seen ballasts that run both T8 and T12 versions, but I am referring to those that only list F30T8 on the label.
Also, can an F34T12 be run on a NPF F40 preheat ballast without any ill effects?
As far as I understand, it all depends on the ballast. Some NPF F30T8 ballasts (especially the ones listed for operation with only F30T8 tubes) will overheat with a F30T12 tube due to the lower arc voltage of the F30T12 since North American F30T12 tubes were originally intended for operation on rapid start ballasts only and some NPF F40T12 preheat ballasts (especially the F40T12 only ballasts) will also overheat with a F34T12 tube installed just like with running F30T12 tubes on F30T8 preheat ballasts. If the ballast lists both F30T12 and F30T8 tubes, then it should be safe to run either F30T12 and F30T8 tubes on that ballast and the same would apply with F40T12 NPF preheat ballasts that list F30T12 tubes and 32w circline lamps, in which it is safe to run F34T12 tubes in this situation.
