Electrical – New Dimmer Switches Work Inconsistently

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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.

Best Answer

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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