We have fluorescent lights in our office and someone said that the ballast was bad. How can you replace a ballast?
Electrical – How to replace a ballast
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Assuming you're talking about motion sensors like this:
Switches like that need power. They can work by trickling current through incandescents if hooked up like a normal single-throw switch (in series with feed going to lights). If the switch has 4 wires (hot, return, switched, and ground) then you can hook them all up and it will power itself using it's own hot + return. In that case, it shouldn't have to trickle power through the light's circuit, and fluorescents should be able to turn off.
My guess would be that because the fixture has a metal frame, the ballast is grounded via its contact with frame. If the frame were plastic, you would need to use the terminal on the ballast.
If you're converting it to hardwired, you should definitely connect the ground wire to the grounding screw.
You're also going to need to cut a hole if there's no punch-out available and make sure to use a cable clamp/strain relief suitable for using with romex.
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Best Answer
Before attempting to replace the ballast, I'd check to make sure it wasn't the bulbs first. If they're blackened at the ends, then it's the bulbs.
Otherwise, it may be the ballast.
First, cut power to the light by flipping the breaker. I'd check to make sure you got the right circuit by flipping the light switch on and off afterwards.
Next, open up the fixture and remove the bulbs. There's usually a center section of the fixture that is held in place by several flanges. Squeeze the center section to remove it.
The ballast should be inside - it looks like a rectangular box. Unscrew the wire nuts attaching it to the fixture. (I replace them on the exposed wire ends afterward just for a little extra safety.) Un-bolt the ballast from the fixture.
Take the ballast to a hardware store and get a matching replacement.
Reverse and repeat.
If you want pictures, here's a tutorial with the same basic approach.
Also, here's another resource that suggests replacing the entire fixture may actually be cheaper.