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How To Replace a Fluorescent Light Ballast

A fluorescent light ballast is an electrical component of fluorescent lights. The new screw-in fluorescent light bulbs (CFL or compact fluorescent lights) have a built-in ballast in their base that works to start the bulb when you turn on the light. There are two basic types of ballasts. Electromagnetic ballasts are used in fluorescent tubes like the four or eight foot long bulbs commonly used in overhead fluorescent light fixtures. Electronic ballasts are used in CFLs or compact fluorescent light bulbs. In both cases, the ballast provides a high initial electrical discharge to start the light bulb burning. Symptoms of a bad ballast include a noisy light fixture and a flickering light bulb. In either case, you can correct the malfunction by replacing the electrical ballast in the fixture.

Removing the light ballast

Noisy fluorescent lights? You may have to change the ballast

Noisy fluorescent lights? You may have to change the ballast

  1. Turn off the light and the power to the light circuit in the electrical panel. If you do not know which circuit controls the light you want to work on, leave the lights on and turn off each circuit breaker in the electrical panel in turn until you find the one that turns off the light. Mark that circuit breaker and seal it in the off position with tape suitably marked.
  2. Remove both fluorescent light bulbs from the fixture. Remove them carefully and set them aside where they will not be broken.
  3. Remove the cover panel from the light fixture by unscrewing the two cap screws that hold the panel in place.
  4. Before disconnecting the electrical wires from the ballast, check for voltage with an electrical tester or multi-meter.

Installing the new ballast

  1. Once you are certain that the power to the ballast is off, check to make sure that you have the proper ballast in hand.
  2. Disconnect each wire from the old ballast and connect it to the same colored wire on the new ballast one at a time.
  3. Use new wire nuts and tighten them securely on each connection.
  4. Support the new ballast while you unscrew the cap nut that holds the old ballast to the base of the light fixture.
  5. Place the new ballast in position and screw the cap nut in place to hold it securely in position.
  6. Gather the wires together in a bundle and secure them with electrical tape or wire ties.
  7. Replace the light fixture cover plate.
  8. Reinstall the light bulbs.
  9. Restore the power.
  10. Turn on the light fixture switch and check that the bulbs light up instantly and burn properly.


Follow good electrical safety precautions while working on fluorescent lights and ballasts. Verify that you are properly insulated from an electrocution hazard by wearing rubber soled shoes, using gloves, if necessary, and not doing any electrical work in a wet environment.

You will have to use a stepladder to change the ballast so make sure the ladder is securely positioned.

It helps to have an assistant to hold tools and the ballasts.

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