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Installed a ceiling fan dimmer switch in a bedroom that is on an arc fault circuit. When pushing the dimmer switch up or down on the ceiling fan, it then trips the GFCI outlet on the bathroom circuit. These are two separate circuits with two separate breakers in the breaker box so I'm perplexed as to why a GFCI outlet on one circuit would trip as a result of something on another circuit. Should I assume something in the breaker box is wired up incorrectly?

  • What make and model are the fan controller and the GFCI in question? – ThreePhaseEel Jul 10 '18 at 22:14
  • When you fit the dimmer switch, did the old switch have a neutral wire attached? Did the new dimmer require a neutral? Where did you obtain this neutral? – Harper Jul 10 '18 at 22:34
  • fan controller is Lutron S2-LFSQH-WH. as for the wiring, the old switch was a basic single pole slip switch. the white neutrals in the box were all tied together. it had black line wire connected to bottom and red wire connected to top which went up to fan where the light/fan wiring in the ceiling was tied together. there is then a third 14/2 romex in the junction box that ties in and goes up and off to somewhere else in the chain. – TXProud76 Jul 11 '18 at 21:53
  • @Harper -- the S2-LFSQ does not use the neutral at all – ThreePhaseEel Jul 22 '18 at 13:44
  • Is this a multi wire branch circuit? – Ed Beal Sep 25 '18 at 16:42
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Try a Lamp Debuzzing Coil on the line-side of the dimmer

This sounds suspiciously like your dimmer is generating some sort of switching trash on the power line that's interfering with the GFCI's circuitry and causing it to trip, since it only happens if you change speeds. The general fix for this sort of interference problem is to wire a Lamp Debuzzing Coil (LDC) (which is a prepackaged choke, basically) in on the line side of the dimmer, as documented in Lutron appnote #519.

If it persists, change the GFCI out for a new one of good quality

If the Lamp Debuzzing Coil doesn't fix it, then I would keep the coil in place (it'll cut down on RF trash coming out of the dimmer in any case) and replace the GFCI with a new one of good make and quality (you want a specification or industrial grade GFCI receptacle or deadfront device here, not the cheapest builder-grade thing you can find).

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