Bizarre Behaviour with CFL Ballast (light turns on when I touch the physical ballast)

Question

I recently took an old ballast I had lying around and installed it as a shop light over my desk. I took an extension cord and stripped the wires and connected all the whites, all the blacks, and attached the ground to the metal fixture itself. I then wired in a switch and plugged it into an outlet.

When I turn the fixture on, the CFL tubes glow a dull orange at each end and will only fully illuminate when I physically touch the fixture and essentially ground it. What did I do wrong?

Note, this doesn't happen all the time. If the fixture has been on for a while and I turn it off and turn it back on, it does so fine w/o me needing to touch it.

Answer 1

This is extremely common behavior for old fluorescent ballasts, though the reason for it depends on exactly what type of ballast it is.

If it is a really old model that uses a replaceable "starter" cartridge, it is likely that the starter needs to be replaced.

If your ballast does not require a starter, the issue most likely the lack of a ground plate behind the bulbs. "Rapid Start" magnetic ballasts require the metal plate that makes up the back of the fixture to be grounded, which provides a pathway for the "radiated" high voltage current that starts the lamp.

If the fixture is already properly grounded and this is still an issue, then it is likely that the ballast is failing and is just too weak to provide a good starting current.