I'm a homeowner replacing an old broken fluorescent light ballast and am not 100% sure about the wiring since the number of wires and the colours have changed. Can someone confirm that my plan is correct?

Old ballast configuration:

Old ballast configuration

New ballast wiring diagram:

New ballast wiring diagram

My planned wiring configuration:

My planned wiring configuration

  • 1
    Can you shoot a photo of the ballast wiring diagram? I see where you hand-drew that, but I do not believe that accurately describes the ballast wiring diagram on the ballast label. I gather that the ballast is rated for 1 tube or two? (common on instant-start ballasts). Note that instant-starts start the tube with a very intense arc, which causes higher startup wear than a rapid-start ballast. This could be an issue for a frequently started lamp such as in a bathroom. Commented Feb 5, 2022 at 22:30
  • Thanks for your response. That's actually a screenshot of the wiring diagram from the manual bulbscanada.com/bob/pdf/FulhamBallast/… (see diagram 3, there isn't one on the ballast itself). It's rated for 1, 2, or 3 tubes and I have 1. The light is in the bathroom.
    – MarcGuay
    Commented Feb 5, 2022 at 22:35
  • Could you verify lamp size matches the ballast? It looks like you had T12 lamps (1.5"dia) and you bought a ballast for T8 lamps (1"dia). Commented Feb 6, 2022 at 0:53
  • @NoSparksPlease I have the WH3 model from that document which seems to support T12.
    – MarcGuay
    Commented Feb 6, 2022 at 2:46

1 Answer 1


Yeah, that's fine. I'm a bit surprised to see the red wires from the ballast merged, but okay.

Since the ballast was previously used for rapid-start (which use the pre-heat filaments on each end of the tubes), it has 2 wires per tube end. I recommend preserving them as much as practicable in case you ever switch back to a rapid-start ballast.

It doesn't really matter where the merge of those 2 wires happens.

  • Thanks. I might contact the seller who suggested this ballast as a replacement for the other one and see if they have a rapid-start version instead.
    – MarcGuay
    Commented Feb 5, 2022 at 22:43
  • 1
    If available in the size of your lamps, I'd go ballast free LED 120 v bulbs, no starters or ballasts to worry about again. Super simple wiring. According to code, the fixture needs to then be labeled that it was converted to 120v LEDs, but that' no big deal. There are 3 types of LED replacement tubes, Here is a link that describes them better than I can. But I'd seriously consider ditching the ballast to accommodate line voltage to the LED tubes w/o a ballast. ...most energy efficient as well.premierltg.com/… Commented Feb 5, 2022 at 23:21
  • @MarcGuay yeah, I deal with places like 1000bulbs.com on ballasts, who tend to know what they're doing. But the key is start with the tube and make sure it (and number of tubes) is on the supported list, and don't read that list optimistically. I'm largely sticking with real fluorescent, but I'll switch to LED if I'm looking at prohibitive costs on ballast or tube. Commented Feb 6, 2022 at 1:56

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