I bought 3 of these to replace 2 out of my 3 twin tube T8 58W fittings which had blown the electronic ballast. The 3rd is a spare in case the 3rd one goes bang. The connection diagram showed the tubes connected in series on these and on the original ballast type it was in parallel. I wired the fitting as the Osram electronic ballast showed but found the lamps only fired twice and stopped. Then I tried it is parallel and it worked better but still had an issue and would not lit the tube. I then swapped the tubes over to ones which were not as used as I noticed that the ends were also a bit black. The new ballast then worked fine with a 2 second delay start which matches the supplied data. I wired the tubes in parallel, if wired in series as the Osram ballast tells you to do and one tube was faulty you loose both in the double fitting. I then put the older tubes with black ends in the original 3rd fitting which was still working and the tubes lit up perfectly. I assume that this may wear out the last original ballast and I will then swap out the ballast and get new tubes at the same time. The only difference between the original ballast is that the new ones do not fire the tube immediately the switch is on, there is a 2 second delay. I think also the Osram may be more sensitive to tubes which are worn or show black near the tube ends as the original ballast does not seem to care as much. May be the Osram ones will last better because of the delay or not burn the tube as much? The original type lasted 10 years so not to bad. I hope to get at least 10 years out of these. The Osram were also longer than the original so I drilled an extra fixing hole in the fitting which was a breeze to do. I knew this before I bought them so I checked it was possible to modify the fitting.