Like other components of light fixtures, ballasts can become faulty over time. If you suspect that your ballast is malfunctioning and needs to be replaced, you should learn how to test a ballast with a multimeter to determine if you can continue letting it support your light system.
In this blog post, we will show you the tools you need and the specific steps to take to get the job done. By the end, you should be able to apply what you have read to test any ballast you have; be it a two wire ballast or test a t8 fluorescent ballast.
For a complete understanding, make sure you read until the end!
- Steps for Checking Ballast With Multimeter
- What You Will Need to Have:
- Step 1: Turn The Power Off
- Step 2: Remove The Cover Of The Light Fixture
- Step 3: Remove The Bulbs/Tubes Of The Light Fixture
- Step 4: Remove The Ballast
- Step 5: Inspect The Ballast Visually
- Step 6: Look At The Wiring
- Step 7: Test The Continuity
- Step 8: Test The Input Voltage
- Step 9: Test The Output Voltage
- Step 10: Replace The Ballast If Necessary & Reassemble The Light Fixture
- How to Tell if Fluorescent Bulb or Ballast is Bad?
Steps for Checking Ballast With Multimeter
Even though it can sound a bit intimidating, checking a ballast with a multimeter is actually very straightforward. Let’s look at each step in detail now!
What You Will Need to Have:
- A multimeter – You can test an electronic ballast with a digital multimeter or an analog one.
- A wrench
- A wire cutter or pair of pliers (If your ballast wiring cannot unclip)
Step 1: Turn The Power Off
The first thing you need to do to test ballast is turn off all the power. This has to be done at the circuit breaker. Flipping the light switch off is not yet foolproof.
Although this might feel like a trivial step, you should never proceed to check a ballast without completing it first. It takes just a couple of seconds but keeps you from getting hurt.
Step 2: Remove The Cover Of The Light Fixture
Once you are sure the power is off, you can go ahead and disassemble your light fixture. Start by taking the outer cover off.
Usually, there will be tabs on the two sides; all you need to do is press them and remove the cover. If you are lucky, you just need to flip the cover open or slide it off. In some cases, though, you might have to do some unscrewing with a wrench.
Step 3: Remove The Bulbs/Tubes Of The Light Fixture
After the cover of the light fixture, remove the light bulbs or tubes. Turn them counterclockwise, making sure to have one hand ready to catch them if they fall unexpectedly.
If they are fixed and cannot be rotated, pull them away from the fixture by the side of the cover.
Step 4: Remove The Ballast
When the light bulbs/tubes are out of the way, you can move onto the ballast. Detach it from the fixture by disconnecting the wires and removing any screws with the appropriate tool.
- If you have a modern ballast, you can just unclip the wires.
- But if your ballast is an older model, use a wire cutter or pair of pliers to do some snipping. Make sure that you do not cut the wiring too close; leaving several inches is best.
If you are worried about your safety while cutting through the wiring, use a non-contact voltage tester to get peace of mind.
Take a photo of the ballast wiring to use as reference when you mount your new ballast in the later steps. It can save you a lot of time and head-scratching!
Step 5: Inspect The Ballast Visually
Now, with the ballast in your hands, take a closer look.
You might be able to detect a bad ballast right away.
If you see bad ballast symptoms, like the ones listed below, you can conclude that it is faulty and must be replaced. No need to continue with this fluorescent light ballast test!
- Damaged ballast casing or housing (For example, it might be swollen, discolored, etc.)
- Burned body and/or wiring
- Oil leaks
Step 6: Look At The Wiring
The next step is to make sense of the different wires: the input wires and output wires. The input wires are the ones coming from the power source into the ballast, while the output ones go from the ballast.
Step 7: Test The Continuity
Turn the multimeter on and set it to the resistance setting at about a thousand ohms. Then, take the probe of the multimeter and touch it to the input wire. The other multimeter probe should touch the output wire. See if your multimeter displays a reading or makes a beeping sound. If it does, your ballast should be fine.
When you test fluorescent light ballasts this way, you are looking at the ballasts’ continuity. If there is no continuity, you are looking at bad ballasts!
Step 8: Test The Input Voltage
Now, move onto testing the voltages of the ballast. Start on the AC voltage mode, which is shown as a voltage symbol with a wavy line on top.
Touch the black probe to the ballast’s black wire and the red probe to the red wire. This checks the input voltage and tells you if there is power going to the ballast. If the multimeter displays a reading, there is power, and vice versa.
Step 9: Test The Output Voltage
Next, proceed to testing ballast output voltage. Touch the wire from the ballast with the red probe and the black probe to the other end of the wire. You should see roughly 120 volts on your multimeter. Otherwise, your ballast is not providing the appropriate voltages to your lights.
Repeat the process with the neutral wire. The red to the end of the wire from the ballast, and the red to the other end. Your multimeter’s reading should be about 0 volts.
Refer to an online ballast output voltage chart if necessary.
Step 10: Replace The Ballast If Necessary & Reassemble The Light Fixture
If you have determined that the ballast is bad, get a new one to replace it. Be sure to reassemble the light fixture carefully.
All you need to do is work backwards: put a new ballast in by rewiring, reinstall the light bulbs/tubes, prop the cover back onto the fixture, and switch the power on. Do not forget to test that your lights are running properly.
That wraps up this guide on how to test a fluorescent ballast using a multimeter. It is not so difficult right? You can definitely do this on your own in under an hour.
How to Tell if Fluorescent Bulb or Ballast is Bad?
In addition to the ballast testing methods above, here is other information on how to tell if a ballast is bad.
To test for a bad ballast, inspect it visually for faulty symptoms (As mentioned briefly above). Then, look at your fixture’s performance.
- If your lights are not turning on, flickering, dimming, or changing in color, then there is a good chance your ballast is fried.
- Other signs include strange humming or buzzing noises, even when the lights are off, and weird odors.
Besides testing a fluorescent ballast with a multimeter, you can try replacing the bulbs and restarting your fixture. If the fixture lights up well after the replacement, you can conclude that the bulbs were bad and not the ballast.
For more details on this matter, check out our other blog post, “3 Ways To Check If The Ballast Is Bad In A Fluorescent Light.”
How to test a ballast with a multimeter? To recap, if your lighting fixture is flickering and dimming or failing to turn on altogether, your ballast is likely faulty. To determine if it is indeed bad, first, turn off the power supply to the lighting fixture and take out any bulb/tube.
Next, use a multimeter to test for continuity between the input and output terminals on the ballast.
Do not ignore the warning signs; replace your worn or damaged ballast promptly to ensure optimal performance of your lighting setup!
Thomas is the Founder of Powercorecard. He is a licensed electrician with more than a decade (15 years to be more specific) of experience in the electrical industry. He has served in multiple capacities, most recently as the Chief Electrical Officer for a respected electric company. His extensive knowledge and experience are the foundation of Powercorecard, particularly his tabs on cutting edge of new technology.