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I have a standard ceiling light fixture with a fan and three light bulbs connected in parallel. The fan still works, but the light bulbs stopped working. I took it apart and tested with a volt meter and discovered the following:

  • The voltage across a light socket is 120V. (In other words, when I screw a light bulb into the socket, it is subject to 120V, at least initially.)
  • But when screw a light bulb into one socket of the fixture, the voltage across the other sockets drops to 5V (or 20V, apparently depending on the type of light bulb).
  • It does no matter which socket receives the light bulb.
  • I tested a few wires inside the fixture and found the same result: the voltage drops when I screw in a light bulb.
  • The light bulbs work in other parts of the house.
  • The fan works regardless of whether the light bulbs are screwed in.

This suggests that something is restricting current flow to the fixture. But what could that be?

Other things to note:

  • I am using 800 lumen and 1600 lumen LED bulbs (i.e., replacements for 60W and 100W).
  • I presume that the lights fail to work because the voltage drops
  • I did not measure in detail which kind of light bulb causes the voltage to drop to 5V and which kind causes the voltage to drop to 20V, and whether the difference comes from voltage or from the manufacturer.
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    If this is a new fan, just return it since it is defective. If an older fan you have had, I would guess a loose connection. Stop using it since a loose connection can heat up, the voltage goes somewhere and can become a toaster. If handy you can probably take it down and repair yourself, hopefully the fan is not sealed.
    – crip659
    Commented Oct 21, 2023 at 19:56

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