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I have a 15 amp breaker that controls:

  1. Three bathroom incandescent vanity lights that have a wall dimmer,
  2. Four incandescent can lights on my lanai that are controlled by four-way switches, one of which is a dimmer,
  3. three GFCI duplex outlets on my lanai.

I have string patio lights (LED) that I am trying to control with a dimmer without success. I have tried three different dimmer configurations

  1. a plug-in smart dimmer,
  2. a simple plug-in sliding lamp dimmer, and
  3. a switch dimmer inserted into the circuit of one of the GFCI outlets.

All three dimmers have the same problem:

  • If the vanity lights and can lights are OFF, all three of the dimmer options for the patio string lights work as expected: they turn the lights on/off and dim them.
  • If I turn on either or both of the vanity lights and/or the can lights, the dimmers for those effect the dimmer for the string lights plugged into the GFCI outlet. Even if I have the string patio lights turned off, turning on the vanity lights or the can lights will turn on the string lights plugged into the outlet. Stranger that that the dimmers on the vanity lights and the can lights will dim the string lights plugged into the outlet.
  • If I remove the dimmer from the string lights and merely plug them into the GFCI outlet, the switches for the vanity lights and can lights have no effect on the string lights...they don't turn the on or off and therefore don't dim them either. It's only when I have a dimmer attached to the GFCI outlet that I experience the problem.

I have removed all three GFCI outlets from their boxes and checked that they are wired properly for line and load connections; they are.

I appreciate any thoughts on why this is happening and solutions to the problem if they exist.

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    What make and model are all the dimmers involved in this situation?
    – ThreePhaseEel
    Apr 15, 2021 at 23:09
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    The existing wall dimmers for the incandescent vanity lights and can lights are: Lutron DV-600P-LA Diva dimmers. The wall dimmer I tried to use with the LED string lights was: Lutron DVWCL-153PH-LA. The smart plug-in dimmer I tried in the GCFI outlet was: Treatlife DP-10 Smart Plug-in Dimmer. The slide style lamp dimmer I tried in the GCFI outlet was: Leviton TBL03-10E Tabletop Slide Control Dimmer. I hope that helps.
    – Don Fischer
    Apr 16, 2021 at 1:18
  • Do you have a voltmeter or multimeter? Also, does power go to the can and vanity lights first, then the GFCIs? Or does it hit the GFCIs first and then the can and/or vanity lights? Or does it sort of "branch" at an upstream point to take separate paths to each?
    – ThreePhaseEel
    Apr 16, 2021 at 1:37
  • Yes, I have a multimeter. I have not climbed through my attic so I am not sure about the branching situation. I do know that the last GFCI outlet in that chain has wires attached only to the line side (no load wires attached) so at least I know the GFCI outlets are downstream or on a separate stream from the vanity lights and can lights.
    – Don Fischer
    Apr 16, 2021 at 12:14
  • A little formatting goes a long way toward readability and comprehension.
    – FreeMan
    Apr 16, 2021 at 12:34

1 Answer 1

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Firstoff, do not put dimmers on receptacles except for testing. That is illegal and dangerous, unless you use a special magic receptacle that's keyed to reject all loads except certain lamps which you put the companion plug on.

If that setup needs GFCI protection, then you would be better off learning all about GFCI's ability to protect downline loads using the "Load" terminals (which you should never use for any other purpose)... and wire it so the dimmer is downline of the GFCI protection. You can't dim GFCIs either.

However, your root problem is miswiring. Somehow the patio lights are in series with the other lights.

The next step here is for you to post pictures of the interior of all boxes. Do not disconnect any devices, but do try to pull things out so we can see how the wires connect to each other and which wires are grouped into which cables.

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    I appreciate your comments. First, I did not wire any of the switches or outlets on the circuit. They were all wired by a licensed, professional electrician when the house was built in 2005. All I've done is taken the three GFCI outlets out of their respective boxes and disconnected them to verify with a voltage meter that the line connections and load connections were in fact wired properly. They were.
    – Don Fischer
    Apr 16, 2021 at 18:44
  • @DonFischer sounds like the last electrician did a bad job. That can happen, particularly with builder electricians who tend to be all about volume. Or someone else's hands got into this in 16 years. Signs are the unworking switches and the use of three GFCIs on one circuit with Load lines in use on two of them.
    – Harper - Reinstate Monica
    Apr 16, 2021 at 21:12

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