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(USA 120v) There are two recessed ceiling lights in the bathroom. The switch is a modern code one that senses if somebody is in bathroom but for years it seems to have been in a mode where it just works like an on/off switch. The switch is in a three-way receptacle that as well as the sensor-type switch has a regular on/off for some wall lights in the bathroom and a timer switch for the bathroom exhaust fan. Yesterday one of the two ceiling lights failed with a bang which blew the circuit breaker. I replaced both lights. Pushed circuit breaker back in. Everything else on that breaker and the other two things in the receptacle work, but the ceiling lights won't turn off. Suspecting that the power surge that popped the breaker damaged the sensor switch I replaced it with a new one, but still I cannot turn off the ceiling lights. Pushing the switch causes the lights to toggle between bright and dim, but they never go out. They're new LEDs. I'm not sure what to do.

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    What make and model are the occupancy sensors involved (both old and new), and can you post photos of the wiring inside the switch box? Nov 11 '20 at 1:25
  • @ThreePhaseEel It seems that the occupancy sensors were passing current that was enough to make the LEDs glow. This was true of the old and the new one which was labelled as LED compatible. The solution was to replace the occupancy sensor with a simple switch. See the answer below. Thanks for your comment.
    – Flynn
    Nov 11 '20 at 3:49
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They're new LEDs.

An ordinary switch turns power totally on and off. However, many special types of switches, often (but not always) including:

  • Dimmers
  • Smart Switches
  • Motion Sensors
  • Photo Sensors (a.k.a. dawn/dusk)
  • Timers

need to have power flowing through constantly in order to power their electronics. There are a few different ways to do this:

  • Batteries - easy, always works, but means changing batteries every year or two, which is something people forget to do.
  • Leak current through the circuit - Easy to design, but very much not compatible with LEDs. Typically results in LEDs blinking or dim.
  • Neutral to complete the circuit - this is, IMHO, the best solution. Except that if you don't have neutral in the box then it doesn't work. Which is why neutral is now required in new installations in most switch boxes.
  • Ground - this is permitted if designed appropriately and very low current used.

Most likely if you swap the sensor switch for a simple switch, everything will work correctly. If you really need (or want) the sensor, then look for one that:

  • Requires ground to function. This will be described in the installation instructions.
  • Requires neutral, provided you have neutral available.
  • Specifically claims "LED compatible". That should mean that it doesn't leak current through the circuit when off.

This problem does not happen with incandescent bulbs, which is likely why you did not have a problem previously.

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    You're exactly right. I replaced the sensor switch with a simple on/off switch and now everything works correctly. The motion sensor must leak current and that's keeping the LEDs on. I also verified that with no switch in the circuit, the LEDs were not lighting so it was definitely the motion sensor switch leaking the current.
    – Flynn
    Nov 11 '20 at 1:42
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    I'd swear I've read this answer, nearly verbatim, on another question somewhere...
    – FreeMan
    Nov 11 '20 at 14:53
  • I'd swear I've written this answer, nearly verbatim, on another question somewhere... :-) Nov 11 '20 at 14:55

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