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I’m redoing a room in my house and I’m replacing a normal switch with a dimmer. I read 120V from hot to ground from the source, and 70V out from the dimmer (Leviton, LED/incandescent compatible). The wiring is pretty straightforward: it’s 2 14/2 wires, whites are connected together with a nut and black from source in the black screw and black that goes to the light on red screw.

Is the 70V after the dimmer normal or it’s faulty? I didn’t connect anything to it yet, I’ve read the reading directly at the end of the wire (about 6 feet).

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You will never get 100% out of a dimmer, but 70 sounds low. Do you have a trueRMS multimeter or a cheapo unit? A non-RMS one could be mis-sampling the AC voltage given the irregular shape of the resulting AC waveform, which can give an off reading.

I would also check again with a load (bulb) in-place. You might not have enough current to get the triac (the component that "dims" AC) to latch (holding current, often >10ma, aka 1.2 watts in USA) early enough in the sine wave. Adding a load will enable everything to work as designed, which could (should?) fix the issue.

  • I will try tonight and report back, thanks! – Simon Arsenault Jul 20 '20 at 13:05
  • I'm not sure I agree with your opening statement. Some dimmers have deliberate full output positions (which presumably bypass the dimming mechanism). – isherwood Jul 20 '20 at 15:12
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    @isherwood, I don't think that's true that dimmers will bypass the dimming mechanism when set to full power. At least none of the cheap ones, since adding that feature would add a fair amount of cost, and most people wouldn't notice any benefit. – Nate S. Jul 20 '20 at 15:47
  • @NateS. The better ones do. It's typically past a detent that can be fairly stiff, so people don't even realize it's there; when they hit the detent they assume they are at the end of travel and push no further. There is often a similar detent at the bottom of range, for hard "off". – Harper - Reinstate Monica Jul 20 '20 at 16:55
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    One Lutron we have running four 100 W equivalent LEDs reads 50 V with the slider on bottom and 114 V with slider on top. There is an adjustment lever under the bezel to vary the low level. Measurement with Fluke 115 trms. The lamps are on. I measured voltage through an Isobar plugged into a receptacle in the base of one of the lamps. – Jim Stewart Jul 20 '20 at 21:45
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If the dimmer in is a dimmed down position, then 70 Volts would be appropriate. Why are you turning on the power before totally finishing the job? People get hurt with loose hot wires.

  • Dimmer is at 100%. I tried at min, still reads 70V. I turned on power to verify voltage only, it’s currently off in the main panel. – Simon Arsenault Jul 19 '20 at 21:47
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    @SimonArsenault Hook it up per the instructions and see what happens. – JACK Jul 19 '20 at 22:28
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    @SimonArsenault follow JACK's recommendation. The only time you should be measuring current is if it's not working as expected. Stopping in the process of wiring each fixture to turn the power on, measure voltage, and turn it back off is very time consuming. I know because when I first started doing wiring on my house, I'd flip the breaker on after wiring up each fixture, just to ensure the breaker didn't trip. After a few, I realized I did know what I was doing and quit bothering with that time consuming and unnecessary step. – FreeMan Jul 20 '20 at 13:06

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