I recently installed some feit retro fit can lights in an older home. Had a regular single pole switch and lights stayed on very dim when switch was off. Replaced switch with a dimmer, same issue. Noticed that when lights are out of metal housing they go off. Any suggestions?

  • Did they ever go completely off? – JACK Aug 11 '19 at 22:14
  • Are these LEDs? Does power come in at the switch or at the light fixture? – ThreePhaseEel Aug 11 '19 at 22:50
  • Is this a duplicate to this question: diy.stackexchange.com/questions/159814/…? – Greg Nickoloff Aug 12 '19 at 2:48
  • They did go off completely but only when taken out of the metal housing. I put electrical tape around the arms to see if the metal arms weren’t touching the metal housing if they would stay off and they did. They are led and power comes from switch but being an older home there was no ground wire – Damon Aug 13 '19 at 0:44

Ordinary switches require only "always-hot" (from supply) and "switched hot" (to the lamp). They do not need neutral. Because of that, many older switch circuits are wired only with always-hot and switched-hot.

There are many switches which do an extra trick - lighted switch, dimmer, motion sensor, smart switch, timer, you name it. They need to power themselves. How? The newer ones attach to always-hot and neutral, getting power the normal way. However many such devices are made to be compatible with old switch wiring.

As it happens, incandescent bulbs are electrically pretty much a dead short when they are off. These powered switches can simply leak current from always hot, through themselves, to switched hot - and the incandescent light will not light enough to be visible. However, LEDs are so efficient that this small current makes them light up slightly.

Your "regular single pole switch" wasn't. It was a lighted switch or some other powered device. That's why it leaked a little bit of power through the LEDs. When you switched to a dimmer, you went out of the frying pan into another frying pan, because again you had a switch that leaked power through the LED.

You need to use powered switches (such as dimmers) that attach to the neutral wire. They will not leak current through the LEDs, and that will quiet them.

Another option is to put a module in parallel with the LEDs that is designed to leak the current that the switch requires, such as Lutron's LUT-MLC module.

  • This can happen with an ordinary single pole switch, too, due to capacitive coupling between the always-hot and the switched-hot in a switch loop. – ThreePhaseEel Aug 12 '19 at 11:35
  • @ThreePhaseEel Clearly, Harper Labs is going to need to play more with phantom voltage; I was always under the impression it had no force behind it. If that kick is anywhere near 10ma, that could kill someone... Which would change how I work! – Harper - Reinstate Monica Aug 12 '19 at 17:10
  • Basically, what happens is that even a mere 1mA of 120VAC is still 120mW, which is enough power to make many cheap LED bulbs light up dimly or blink. (Better ones include a bleeder/load resistor across the LEDs to keep this from happening.) – ThreePhaseEel Aug 14 '19 at 23:38

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.