How to Tell If a Ballast Is Bad With an Electrical Meter?
- 1). Verify that the power to the light is on at the main service panel, by checking the labeled circuit breaker. The circuit breaker should be pushed over to the labeled "on" side of the panel.
- 2). Verify the light switch to the light in question is turned on as well.
- 3). Remove each of the fluorescent light bulbs from the fixture. Carefully set them down on a table, and out of the work area.
- 4). Remove the bottom panel of the fluorescent, using the screwdriver to unscrew the sheet metal screws. If your model light uses twist locks rather than screws, turn them 90 degrees in either direction to unlock the cover panel on the bottom. Set the panel carefully on the table.
- 5). Look over the ballast very carefully for any leaking oil. If the ballast is leaking oil, it is bad and needs replacing. The oil is used to cool the transformer inside the case, which should be sealed at all times.
- 6). Check the high and low voltage sides of the ballast using the voltmeter. Turn the meter on and set it to the Ohm setting. Locate the yellow or blue power wire and the white neutral wire running to the tombstone fixture (location where the bulb connects to the light fixture). In any order, clip one test lead to either the yellow or blue wire and the remaining test lead to the white wire. The meter will indicate either a short or a continuous circuit. If the reading is anything other than this, the ballast is bad and needs replacing. Repeat this step to check any additional pairs of wires on the high and low voltage sides of the ballast.
- 7). Locate the entry point of the main power feed line coming into the light fixture next to the ballast. You will see a black wire and a white wire connected to the wiring of the ballast with wire nuts. Unscrew the wire nuts in a counterclockwise direction, and set them aside. Clip one test lead to the black wire, and the remaining test lead to the white wire. You should see the voltmeter indicate a short or continuous circuit. If there is any other reading, the ballast is bad and needs replacing.
- 8). Check the physical condition of each of the tombstone fixtures and ensure they are not broken or chipped, and that the metal contacts are not corroded. If you see damage, replace the light fixture itself.
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