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I bought a Lutron TGCL-153PH-WH 3-way dimmer switch, and I have been having trouble with my three-way wiring. I decided to see if my 3-way switch was faulty, and I conducted an ohm test with my multi-meter.

When touching one probe to the common screw and one to one of the traveler screws, I get a reading when the switch is flipped up or down. However, when I touch the probe to the common screw and the other probe to the other traveler screw, I get no reading if the switch is flipped up or down.

Thinking this switch was faulty, I brought the switch back and purchased another one. The newest switch gives me no readings when connecting the common to either of the traveler screws. Am I testing these switches correctly? Are one or both of these switches faulty?

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  • Is there continuity between any pairs of screws? (There aren't many combinations to try) The labeling may be getting confused by the competing meanings of "common" in electrical wiring. How is the dimmer slider positioned?
    – Ben Voigt
    Commented Feb 1 at 22:42
  • Dimmer is positioned all the way up. By common I mean the screw that is different from the other two. Commented Feb 1 at 22:53

1 Answer 1

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Continuity testing works with a simple switch. That's a switch with no:

  • WiFi
  • Timer
  • Dimmer
  • Other "smart" functions

Why? Because a simple switch simply makes or breaks an electrical connection. A smart switch does a whole lot more to electronically route power between terminals. But it is also using some of that power to do its magic.

As a result, when it is not powered on, flipping the switch will likely have no effect. In addition, depending on the nature of the electronics inside the switch, the "continuity" may at that point show "on" or "off" as far as a multimeter is concerned but that doesn't mean it will or won't conduct AC 120V electricity when it is powered on.

When it is powered on, the electronics do their magic which can include an additional complication: dimming. A dimmer doesn't simply let more or less electricity in, the way a variable resistor (rheostat) would do (and the way I used to think dimmers worked when I was much younger). It actually chops up the incoming power in a way that the lights understand as dimming (gross oversimplification). So there is no guarantee of anything.

The proper test, unless the manufacturer has other trouble-shooting procedures, is to test the switch locally as a single (not 3-way) switch. In other words:

  • Connect hot (line), switched hot (load), neutral, ground as directed by the installation instructions. This will vary by model - some will use neutral and some won't, some will use ground and some won't. Configure any additional connections used for 3-way setups as if this is a simple (not 3-way) configuration.

Then you have two options, depending on materials on hand and depending on the particular switch box wiring (you can't wire a light to neutral at the switch box if you don't have neutral in the switch box).

  • Wire a light fixture temporarily directly to switched hot (load) and neutral. Turn on the breaker and test.

or

  • Connect one traveler to the switched hot (load) connection on your new switch.
  • Turn on the breaker.
  • Turn on the new switch.
  • If the light comes on, great. If the light does not come on, flip the 3-way switch. If the light still doesn't come on then you either have a loose or broken connection or a bad new switch.

Continuity only enters into the trouble-shooting here in two ways:

  • Checking any existing simple (regular or 3-way) switches that are still part of the circuit.
  • Identifying wires. This can be important with 3-way switches as there are so many possible variations. Turn off the breaker. Take two wires in a /3 cable and connect them together. Go to the other end of the wires (i.e., the other switch box) and check which wires have continuity - you should have 2 out of 3, in which case the 3rd wire in each cable is the same wire in each box. Repeat until you have all 3 identified.

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