I am trying to identify the blown varistor from my fluorescent light tube when I was trying to fix it.

I have never seen a manufacturer marking logo on it with a "W" and a cross in the middle. Not sure what the "P050" means but I think "250" could be the voltage tolerance.

It'll be a great help if somebody knows what the specifications are.

  • I found the part for the Dark Red capacitor to replace it.
  • The diameter across the varistor is about 7.5mm in diameter.
  • The varistor is across the input supply.
  • I'm not quite sure for the voltage rating of the ballast probably 220V...? I'm in a European country.

photo showing unknown device

  • \$\begingroup\$ I don't think you're going to get very good cost effect repairing old ballasts. They're so common you should be able to find a replacement cheaper than the sum of the parts. \$\endgroup\$
    – K H
    Mar 3, 2021 at 8:43
  • \$\begingroup\$ Yeah, I know about that. Just a bit curious what's the specs for that part is as didn't see that manufacturer logo before. \$\endgroup\$ Mar 3, 2021 at 11:19
  • \$\begingroup\$ @RichardTan - Thanks. Those were not the answers I expected :-( 7mm is another standard varistor size, so it seems that it's not a 5mm device. Also 250V would be an unusual rating for a varistor across a 220V supply (look at the allowed voltage range on European mains supply voltages and you'll see why). I recommend you check the actual rating on the ballast's label etc, if you're not sure || I will edit the question for you, to add those details, and then remove the previous comments to remove duplication. Those extra details might help someone else. \$\endgroup\$
    – SamGibson
    Mar 3, 2021 at 16:52
  • \$\begingroup\$ @SamGibson - Thanks a lot for adding the details in the post! Yeah, I was trying to find the datasheet from the marking, unfortunately I can't find the manufacturer with that logo. Hope someone who knows about the manufacturer logo cross by. \$\endgroup\$ Mar 3, 2021 at 20:42
  • \$\begingroup\$ Best guess is 50 J and 250 V rating. Try to figure out which company that logo belongs to. That capacitor next to it does not look happy. \$\endgroup\$
    – winny
    May 26, 2021 at 10:10

1 Answer 1


It seems like it's not a varistor even though it looks like one. It was actually the PPTC polyswitch, as when I carried out the continuity test on a good ballast, it gave a beep and the resistance measure without the PCB is around 1 Ohm which is unusual for a varistor. When I connect it to the Power supply, it begin to trip around 0.1A and heating up, once it cools down, it able to work again. So, it is a resettable fuse.


Found the similar specs on the link, so I think it should be ok.


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