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I have an LED light bulb on a dimmer switch that will not stay on. If we turn it on just a little bit, it will stay on for a longer time. If we turn it on to full power, it will stay on for a shorter time. If I replace the LED bulb with an incandescent bulb and turn it on, it will go out almost immediately. It appears that the more current that flows through the circuit, the more quickly the light will turn off. The circuit breaker does not trip. There appears to be no great amount of heat generated in the dimmer switch or the light fixture.

I have replaced the dimmer switch once, already, but this did not fix the issue.

The problem may be in the wiring, but I'm at a loss how. Originally, the dimmer switch fed power to a socket. A 2-conductor cable (plus ground) ran power on one wire from the socket's junction box to the dimmer switch, and the return line fed switched power to one of the sockets. I rewired the circuit by inserting a junction box midway between the socket and the dimmer switch and using the two conductors to run hot and neutral there from the socket. From the junction box, the two conductors are used as before: One carries hot, the other is switched. In the junction box, the switched return leg from the dimmer and neutral and ground from the socket are wired to a light fixture. This same setup works flawlessly in the room next door.

Can anyone point me to what the issue could be?

Edit: Pictures of junction boxes

Dimmer junction box

Junction box in wall that feeds this circuit

In the ceiling junction box, hot is wired directly through to the dimmer switch, while the return leg from the dimmer switch (on a white wire marked with black tape) is wired to hot on the fixture. Neutral from the feed is wired to neutral on the fixture. Ground is distributed to the fixture, the dimmer switch, and the junction box support beam. Ceiling junction box for lamp

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    After the light goes out, if you turn the switch off and back on, does the light come back on? Or do you mean "the bulb burns out, never to be used again"? Pictures of the various junction boxes involved (receptacle, switch, junction in the middle) would help. Dec 28, 2021 at 12:15
  • "I'm at a loss how" it's a mystery of science... Seriously the problem isn't necessarily between the dimmer and lamp. Regardless you have to "cross off the dimmer" by replacing it with a plain switch, as it is at least 50% likely to be the problem. Dec 28, 2021 at 23:16
  • @manassehkatz-Moving2Codidact, if we turn the dimmer off after the light goes out and wait for some time, then the dimmer switch will work again. So, the light bulb itself is not affected. I will post pictures as soon as I can.
    – matmat
    Dec 29, 2021 at 8:01
  • @Harper-ReinstateMonica, good idea to take the dimmer switch out of the equation. I will replace it tomorrow with a fixed switch and report back.
    – matmat
    Dec 29, 2021 at 8:01
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    @Harper-ReinstateMonica, I replaced the dimmer switch with a simple contact switch. Imagine my surprise when the behavior persisted! From this point, it was just a few minutes with a multimeter to realize the problem was actually in the light fixture.
    – matmat
    Dec 30, 2021 at 23:54

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The problem turned out to be that this fixture (IKEA Sinnrik) has a resettable fuse inside that is supposed to limit power to around 6 W (fuse part number HR250-110). When I used an 11 W LED bulb, it would work for a while, but the fuse would always trip. After shutting the light off, the fuse would reset after some time and the light would work again. Looking for problems in the wiring appears to have been a red herring!

Thanks for taking and look and offering suggestions, everyone. I've decided to replace the fixture with something that can handle a bit more power, as we need more light than a 6 W LED can provide.

Resettable poly fuse inside light fixture

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    Very interesting the problem and an impressive amount of work to identify the extra-protection that became a headache. One suggestion would be to replace the PTC (resettable fuse) by another one larger - or just put two (or three) equal ones in parallel to double/triple the current capacity. This also could be good to protect the plastic receptacle from overheating.
    – EJE
    Jan 21 at 2:29

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