Wireman · Fluorescent ballast or LED driver failure: troubleshooting for electricians · 2023 NEC ·

Fluorescent ballast or LED driver failure

Tubes dark, flickering or glowing at the ends, or an LED fixture that’s dead with power at it. Ballast, driver, lamp or socket.

Before you start

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How it works

A fluorescent lamp can’t run straight off the line. The ballast strikes the arc and then limits the current. Instant-start electronic ballasts usually run their lamps in parallel, so one dead lamp leaves the others lit, while many rapid and programmed-start ballasts run lamps in series, so one bad lamp can take out the pair. An LED fixture uses a driver instead: it turns line AC into a regulated DC output for the LED board, and its label lists the input voltage and the output current and voltage range. LED tubes come in types: Type A runs on the existing ballast, Type B bypasses the ballast and puts line voltage on the sockets, and Type C uses a separate driver.

Step by stepFull flowchart

Every question and answer in this guide. Tap “Step by step” to walk through it.

What’s in the fixture?
- Fluorescent tubesWhat do the tubes do?
  - One lamp out, or the ends glow orangeTest: Swap lamps and check the sockets
    - Works with new lampsWorn-out lamps
    - A socket is cracked, burned or looseA damaged lamp socket
    - Still out or still flickersTest: Measure the ballast inputExpect: Line voltage within the ballast’s labeled input range.
      - Correct voltage at the inputA failed ballast
      - No voltage at the inputNo power reaching the fixture
      - Wrong voltage for the ballast labelThe ballast is on the wrong voltage
  - Flicker, slow start or a loud humTest: Swap lamps and check the sockets
    - Works with new lampsWorn-out lamps
    - A socket is cracked, burned or looseA damaged lamp socket
    - Still out or still flickersTest: Measure the ballast inputExpect: Line voltage within the ballast’s labeled input range.
      - Correct voltage at the inputA failed ballast
      - No voltage at the inputNo power reaching the fixture
      - Wrong voltage for the ballast labelThe ballast is on the wrong voltage
  - Every lamp darkTest: Measure the ballast inputExpect: Line voltage within the ballast’s labeled input range.
    - Correct voltage at the inputA failed ballast
    - No voltage at the inputNo power reaching the fixture
    - Wrong voltage for the ballast labelThe ballast is on the wrong voltage
- LED tubes in an old fluorescent fixtureWhich kind of LED tube is it?
  - Type A (runs on the ballast)A Type A tube on a failed or incompatible ballast
  - Type B (ballast bypassed)Test: Measure at the sockets of a Type B tubeExpect: Line voltage across the contacts the tube label calls for, and nothing on the contacts it says stay dead.
    - Voltage where the label calls for itA failed LED tube
    - Voltage on the wrong contactsSockets wired for the wrong tube style
    - No voltage at the socketsNo power reaching the fixture
  - Type C (remote driver)Test: Measure the driver inputExpect: Line voltage within the driver’s labeled input range.
    - Correct voltage at the inputTest: Measure the driver outputExpect: DC voltage within the label’s output range while the LEDs are lit.
      - No DC outputA failed LED driver
      - Output in range, LEDs darkLED board or connector failure
      - Lit but stuck dimDimming leads holding the fixture at low output
      - Output cycles on and offDriver overheating or protecting itself
    - No voltage at the inputNo power reaching the fixture
- Integrated LED fixture with a driverTest: Measure the driver inputExpect: Line voltage within the driver’s labeled input range.
  - Correct voltage at the inputTest: Measure the driver outputExpect: DC voltage within the label’s output range while the LEDs are lit.
    - No DC outputA failed LED driver
    - Output in range, LEDs darkLED board or connector failure
    - Lit but stuck dimDimming leads holding the fixture at low output
    - Output cycles on and offDriver overheating or protecting itself
  - No voltage at the inputNo power reaching the fixture