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How to test a fluorescent ballast

Updated July 20, 2017

When a fluorescent light fixture is buzzing, flickering or not turning on, the ballast may be malfunctioning. A qualified electrician can safely troubleshoot problems in your fixture. If you would like to do the troubleshooting yourself, however, opening the fixture to examine and test the ballast can help you determine whether it's causing the problem.

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  1. Turn off the power running to the fluorescent light fixture.

  2. Open the lens and remove the lamps and ballast cover. If you notice any obvious signs of wear on the ballast, such as cracks or leaks, the ballast needs to be replaced.

  3. Check for loose or exposed wires. Make sure all wires are making proper connections that follow the diagram shown on your ballast.

  4. Set the multimeter to the continuity function. Touch one prong to a power wire on the ballast and the other prong to the neutral wire. In a ballast, blue or yellow wires are the power and the white is the neutral. If the multimeter fails to light up or beep, a problem with the ballast is keeping the circuit in the fixture open and the ballast needs to be replaced.

  5. Replace the ballast cover and lamps before turning on the power.

  6. Warning

    If the fixture is smoking, sparking or wet, do not attempt any repairs and call an electrician.

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Things You'll Need

  • Digital multimeter

About the Author

Kathleen Michelau is a professional writer who received the President's Scholarship for Journalism in 2002 and holds a Bachelor of Arts in journalism and philosophy from the University of Dayton. She is a Chicagoan who enjoys writing about home repair, hobbies and electronics.

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