I am fixing the lighting in an older building and one of the plastic tombstones has melted.

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There are approximately 100+ tombstones and one has melted. A search found a forum discussion that indicated:

lamps that were supplied to me were made for magnetic ballasts not electronic ballasts

I would think that it takes a combination of significant power and current to generate the heat necessary to melt plastic. I have new bulbs of unknown age for replacing bulb failures and in this case tombstone failure: the bulb was removed before my custody of the project.


  1. How can I determine if the bulb is made for a magnetic ballast an not electronic ballast?

  2. Can I determine if the ballast is magnetic or electronic with minimal effort (i.e. not opening the fixture and measuring from the tombstone)?

  3. Are there any other reasons that would cause a meltdown and how can I test / confirm


  • Wiring configuration is dual-ended
  • T5 Bulbs

2 Answers 2


Keep that is the guess of some yo-yo's on a discussion forum, and even though it's an electrician forum, fluorescent internals are not really their bailiwick. (Being unclear on whether T8 and T12 have same pin spacing? Please.)

But it's not untrue; instant-start ballasts can have some fairly impressive arcing, since they see bad contact in a tombstone as the lamp being unstruck, so they bump the voltage to strike the lamp. This is series arcing. That is a bug in instant-start (one wire per lamp end) ballasts, and I have not seen it in rapid-start or programmed-start ballasts.

The root cause is still a tombstone or lamp fitment problem.

And by the way, that kind of burn-up is why I do not like the idea of 120V on a tombstone, as single-ended LED tubes require.

All electronic ballasts can be excluded by the fact that they flicker much faster than 120 Hz. Spin a pinwheel or anything like that with the light in the background, even just waving your hand across may suffice. If you get the stroboscopic "wagon wheels going backwards" effect, it's magnetic.

  • I think I totally agree , I don't like to do LED single end upgrades but have to on T5 lamps. In my own shop 2 years ago I had horrible problems with my t8 lamps and the radio. The root cause was from contacts getting loose after tons of hay was loaded on a common wall, at work I find overheated tombstones fall apart from one reason or another but a bad connection can be the root cause.+
    – Ed Beal
    Commented Dec 9, 2018 at 23:40
  • I think that arc-fault breakers would trip on the 120V LED scenario mentioned (I hope) but I guess they probably would not if you had bad contacts on a traditional fluorescent lamp + ballast? Commented May 21, 2021 at 12:01
  1. Lamps are made to be used on both electronic and magnetic ballasts.

  2. I have a meter that identifies magnetic and electronic from the ground. They cost about $100.00 and are not a stock item. You can order one from any ballast manufacturer.

  3. Meltdowns are caused by loose fitting lamps. The spring loaded contact and the pin from the lamps keep arcing during use and that creates heat then melts the plastic insulation.Generally over time they become loose from changing out fixtures or they were just manufactured from a low quality vendor. In short it is not an uncommon problem.

Hope this helps.

  • 1
    You can also identify magnetic ballasts from their 60Hz (actually 120Hz) flicker. Spin a pinwheel or...anything with the light in the background, if you get the stroboscopic "wagon wheels going backwards" effect, it's magnetic. Commented Dec 8, 2018 at 21:09
  • Yes, very helpful. With regard to comment 3: if there is any suggestion what I can do to select quality parts or other decisions I can make to prevent arcing this would be exceptionally helpful. I think you are saying that lamps matching ballast types are not the cause of the problem.
    – gatorback
    Commented Dec 8, 2018 at 23:21
  • 1
    @gatorback - My only recommendation would be to try and purchase from a known manufacture like GE, Lithonia, etc., but I would also say that this doesn't occur enough to be a problem over the life of a fixture. Most of the time they occur within five to ten years of use, and that would be a commercial operation where the fixtures run 10 - 14 hours per day. Commented Dec 9, 2018 at 15:38

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