I recently undertook a small project replacing a single toggle light switch with a Z-wave enabled dimmer switch, which is also wired to a fan toggle (a knob with 3 speed settings) in a 2-gang case. The original switch and the fan toggle share a hot wire, which I had to cut and splice due to the way the builder had installed it originally (it was just a loop of exposed wire which wrapped around one of the switch's poles). Everything went pretty well (aside from the dimmable CFLs not being as awesome as I would like, but that's tangental), but sometimes when I turn the fan to a different speed, the lights will turn off, but the switch still has power as evidenced by the blue LED at the bottom.

Now, I've done a small bit of experimentation, and this seems to only happen if you turn change the switch rapidly from one speed to another. If you wait about 20-30 seconds between switches, it doesn't do it.

What could be wrong here?

Edit: More Relevant information. The Z-Wave dimmer is rather sensitive, so if it were to lose power for any period of time it would reset to off, which is probably what is happening here.


Pardon my poor diagramming skills, I was never any good at cad.


As you can see, the bottom wire was just wrapped around the bottom pole of the toggle switch, then ran into a wire cap, where it was connected with the fan toggle. Before


So, I cut the loop, and then twisted it together to splice the two wires together, so that I could also splice in the wire coming from the Z-Wave switch.



Annotated Picture Box

So here's what's going on in there.

Also, I took some voltage readings. When the Light is off, it is measuring 83v (which I think is normal for a Z-Wave switch, to power its wifi). When the light is all the way on, it reads 13v.

When the fan is off, it is at 122v. On speed setting 1, it is 115v. On 2, 100v. On 3, I can't get a reading at all.

  • wow - in all my years of building DIY i never heard of something like that.. must be something in the middle causing a problem. can you post a picture of the wirigin? or make diagram.. there must be something wrong there. Is there voltage on the light when it 'goes off' Be careful as it could electrocute you (it might have a lower voltage, or a voltage leak) Make sure you have somebody with you just in case.
    – Piotr Kula
    Aug 17, 2011 at 9:27
  • Is it 2 independent switches, or a single unit that controls both the light and the fan?
    – Tester101
    Aug 17, 2011 at 12:12
  • @ppumkin I have not yet tried checking the voltage while it cuts off, because I was a bit afraid of the electrocution bit. But sure, I can make you a diagram, and get you a picture of the current situation later today.
    – Cthos
    Aug 17, 2011 at 14:00
  • @Tester101 It is 2 switches, one controlling the lights, the second controlling the fan.
    – Cthos
    Aug 17, 2011 at 14:01
  • 1
    It would be useful to see all the wires, labelled with where they're going. I'm tempted right now to say that probably the dimmer is sensitive to electrical noise generated by the fan motor or switch, but without seeing the full wiring diagram I can't rule out a cross connection between something.
    – gregmac
    Aug 17, 2011 at 17:39

2 Answers 2


Your wiring looks okay (except for the redundant "power to dimmer" and "power to fan" wires -- as I commented, you don't need the extra pigtails, just connect the switches directly with one marette).

I can think of 3 possibilities:

  • The z-wave dimmer is not operating properly with the CFL. Try using a regular incandescent or halogen bulb, and see if the problem goes away.
  • The z-wave dimmer is being affected by the electrical/RF noise that the fan generates when it turns on. Ensure the fan switch is designed to handle inductive loads, or try replacing it with another brand of switch.
  • The z-wave dimmer is defective.

If you have separate cables leading to the fan and light, you'll want to end up with something like figure 1 below. More likely the fan and light are one unit, and there is 3 wire cable running to it from the switch. In this situation, you want to end up with figure 2 below.

enter image description here

Once that is sorted out, you can start to diagnose your problem.

It may be possible that the dimmer has a protection circuit to protect it from voltage fluctuations, or some other internal circuitry that is sensitive to voltage fluctuations. If this is the case, rapidly changing the fan speed may be just enough to mess with it. This might be especially evident when going from [fan off] to [fan high], as motors tend to draw more power than other fixtures especially when starting.

  • It is the latter situation, and the current configuration looks like Figure 2.
    – Cthos
    Aug 17, 2011 at 22:34

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.