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I recently installed 2 new dimmer switches for new construction recessed lights in my living room (LED bulbs). At first these dimmer switches appeared to be working without issue.

However, a few day later I installed a doorbell transformer off of the same circuit that the dimmers are on. Later that day I noticed that the switches weren't turning on my lights anymore. I came back later and tried again and it worked. So then I proceeded to hit each switch a number of times, and noticed that sometimes the lights would turn on, and other times they wouldn't. I could not discern any noticeable pattern, it seemed totally random if they would turn on or not. Also of note, this dimmer has a locator light that turns off when the lights turn on. However, when the switch is flipped and the lights DON'T turn on, the locator light stays on.

I have not yet tried disconnecting the doorbell transformer to see if the switches go back to normal (quite certain this problem didn't exist before the transformer). I am going to try that tonight, but I don't see why that would affect anything.

Has anyone experienced this before? Any ideas on what may be wrong here?

The switch in question is a Legrand Radiant Tru-Universal dimmer switch.

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  • I'd check for loose/poor connections at the switches.
    – isherwood
    Commented Sep 3, 2019 at 15:42

2 Answers 2

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Since the problem started when you added the transformer, that is the first thing to check. Three possibilities:

  • You somehow wired it into the circuit in a way that it ended up in series with the dimmers/lights. That would be rather unusual, and with incandescent lights you'd probably have no lights at all. But LEDs don't need much power, so you just might end up with a "sometimes works" situation as you described.
  • Bad connections. If you spliced in hot & neutral for the transformer so that the lighting part of the circuit is on the same wire nut (or other splice) then a bad connection could cause high resistance and strange problems.
  • An actual interaction between the transformer and the dimmer/LEDs. Unlikely, as a transformer is a pretty simple device.

Disconnect the Transformer

Disconnect the transformer and see what happens to the lights. If that fixes the problem then you need to try:

  • Make sure the transformer is NOT in series. If you are not sure, post pictures of the wires in the boxes for the transformer and the dimmers.
  • Reconnect the transformer, checking connections carefully. If you use wire nuts, get a new set of wire nuts and make sure they are the right size for the number & size of wires.

And if all else fails, move the transformer to a different circuit.

If removing the transformer does NOT fix the problem, check/redo all the connections for the dimmers & lights. If that doesn't solve the problem, replace the dimmers with regular switches and see if the problem goes away - that will tell you if the problem is the dimmers or the LEDs.

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    I didn't think about the fact that "LEDs don't need much power". That certainly makes the inconsistency more understandable. As mentioned in another comment (I should have stated in OP), the transformer is installed at the very beginning of the circuit right off of the panel box. Coming straight off the breaker I have the hot/neutral/ground wires spliced with wire nuts to split to the transformer and then off to my switches. As stated, I intend to disconnect the transformer tonight to troubleshoot. Now I will be sure to check the wire nuts are providing a good connection when reconnected!
    – Scheer
    Commented Sep 3, 2019 at 16:17
  • Also, because the transformer in installed right next to the panel box, the original plan was to just put it on its own circuit (I have plenty of open spaces). Then I felt a bit silly putting a doorbell on its own circuit, so I decided to split off of this lighting circuit instead. But I can always put it on its own if needed.
    – Scheer
    Commented Sep 3, 2019 at 16:20
  • A doorbell transformer doesn't use much power, so sharing the circuit makes a lot of sense.
    – manassehkatz-Moving 2 Codidact
    Commented Sep 3, 2019 at 16:21
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    Do the wire nuts all survive a "pull test" without using tape?
    – Harper - Reinstate Monica
    Commented Sep 3, 2019 at 17:56
  • They did at the time I believe, but it is possible I missed one. I will give that a shot tonight when I troubleshoot!
    – Scheer
    Commented Sep 3, 2019 at 18:50
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I am assuming you installed the transformer ahead of the switches. One question, did you turn off the circuit at the breaker before you installed the transformer. Electronic devices are real sensitive to this sort of thing. If you didn't turn the circuit off while installing the transformer you may have burnt out the dimmers.

If what I just wrote does not apply, you can go into Legrands web site and pull up the Legrand Radiant Tru-Universal dimmer switch installation instructions PDF. I noticed they are programmable and may need to be reprogrammed. These are decent dimmers and also pricey so I would try that before going out and buying more.

Good luck

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  • Thanks for the comments. To clarify a bit, the transformer was indeed installed prior to the switches on the circuit (at the panel box in fact). The circuit was turned off throughout installation of the transformer. Concerning burnout of the dimmers, I should note that when the lights DO turn on, the dimmer slides work as expected. I'll give the installation instructions another read. I think they are being calibrated correctly with the initial power on auto-calibration, but I dont' recall exactly what I did the first time I tested them.
    – Scheer
    Commented Sep 3, 2019 at 16:00

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