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I am trying to install a FEIT Smart Dimmer switch with a 3-way switch. It is an interesting installation where the 3-way switch (works as a single pole in this installation) has 120V line. One of the traveler lines T1 actually gets shorted to 120V line.

The dimmer uses this to get the 120V hot via T1 and the T2 line tells the dimmer whether to "toggle" the state of the switch. In principle this works but not in my house.

The 3-way (single pole) switch had no effect on turning off the lights so I used a multi-meter to see that if I connect 120V to one traveler light T1, then the T2 traveler had 45V on it. Strange, It was triggering the NCV tester as well.

Any idea why this might happen?

I used a continuity tester and confirmed that the traveler wires T1 and T2 are not shorted/connected. But still T2 has some 45V AC voltage on it when T1 is connected to live/hot wire.

In the following diagram T2 is what always has some potential of ~45V.

Official Installation Diagram

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    There are at least 5 ways to wire a 3-way switch. It looks like you cribbed these drawings from a book. Are you sure these drawings correspond to your actual arrangement? Dec 20 '20 at 23:40
  • Thanks Harper. This diagram is what the FEIT installation manual came with.
    – Guraaf
    Dec 22 '20 at 2:20
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T2 has some 45V AC voltage on it when T1 is connected to live/hot wire.

Possibly a red herring. I had a similar experience when installing a similar 3-way-compatible "smart" switch (but with a timer feature instead of dimmer). When I asked the electrician about it, they said that if there's any current flowing in wires adjacent to the traveler, especially along long distances, smaller voltages can be induced in the traveler itself.

More important is to verify that you're using the correct configuration. With a 3-way switch, the line voltage comes in at one switch, and then the load is connected at the other switch. These smart switches can be installed at either end, but the wiring configuration is different depending on which end.

The diagram you show is correct for when you want to install the smart switch at the load end, and your summary of the operation of this configuration is consistent with that as well. But that doesn't mean that's actually where you installed the switch.

You should verify that what you believe to be the "load" wire is in fact the load wire, and not the line supply wire, and vice a versa. If it's not, i.e. if the wire you've treated as "load" shows 120V between it and neutral with your multimeter, then you've got the wrong diagram for where you are trying to install the switch.

If that's the case, then you can either install the switch at the other end of the circuit using the diagram you have, or find the diagram that corresponds to installing the switch at the line end of the circuit (it's probably a similar diagram, except that on the smart switch end, the "load" and T1 wires will be connected reverse from what you have).

I have installed a number of this sort of switch in my own house, and have found them to be reliable, but one has to be very careful to follow the instructions precisely.

If you're sure you've identified your wires correctly, and you're sure you're making all the connections correctly, then it's actually possible you have a defective switch. But you'll want to double- and triple-check everything just to make sure, before getting the switch replaced.

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  • Thanks @Peter Duniho. The smart dimmer can only be installed on the load end. Not on the live input. It has to drive the load as it doesn't short the traveler wire. It actually detects the traveler wire to change state (0 to 1 or 1 to 0) and then toggles its own output state. I did verify 100% about which side is load and which is live. If the traveler has potential then the smart dimmer doesn't ever detect a toggle and hence the 3-way switch feature is lost. Thanks!
    – Guraaf
    Dec 23 '20 at 14:13
  • @Guraaf: "If the traveler has potential then the smart dimmer doesn't ever detect a toggle and hence the 3-way switch feature is lost" -- okay, if you say so. I can tell you with 100% certainty that it is possible to design such a switch that can be installed at either end. But, it's true it's more complicated to design it that way, and it's certainly possible the switch you have isn't designed that way. Dec 23 '20 at 17:07

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