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I’ve wired a Lutron MS-VPS5M (vacancy, supports 3-way wiring) switch to the inside of a walk-in closet, so it will turn off 5 min after someone departs the closet. I’ve also wired 3-way dimmer switch on the outside of the closet, but couldn’t get it to dim. Off & on toggle was not perfect either, though it’d go off, and on, sometimes with two toggles.

I’d like it for the dimmer switch outside to be flipped to turn on (or off) the light in closet, and rectangular push button on Lutron inside closet also pushed to turn on (or off) light if you don’t turn it on before walking in. Lutron works fine to turn off light in ~ 5 min after last motion detected in closet. It also worked on & off manually with a push.

However, although I have dimmable LED bulbs (not CFL), the dimmer doesn’t work!

Can anyone explain why?

Is it not possible to have a smart switch (Lutron) and a dimmer as second switch? I’d like “whatever level is set (outside closet) as dimming level to be what light is emitted” whether turned on by Lutron or turned on by toggle outside closet.

I do realize that the dimmer switch needs to be wired as a single-pole with the Lutron on the other end, because the Lutron deals with the 3-way part, however I’m not sure I’ve wired the dimmer correctly even though the toggle works on both ends. I have hot, and two travelers (one for dimmer, another going to one side of Lutron, and the hot itself, so four wires in dimmer switch box.

Is this possible? If so, have I wired it wrong to get just toggling but no dimming?

Thanks for any advice or help you can provide!

(N.B., the bulbs in the leg [lights in load] are ‘fully dimmable 10%-100% using LED compatible dimmer’ and are Great Eagle Model # 4G240930DA which are ‘two prong’ A19 GU24 base, which I have no other fixtures for—none that are ‘two prong’—-so I cannot test dimming in some other lamp or overhead ceiling fixture). Is it possible these bulbs are defective and don’t really dim? I’m guessing not and it’s that I cannot wire dimmer in 3-way fashion to Lutron vacancy sensor switch.)

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    Start by bypassing the occupancy sensor and see if your dimmer switch works as expected.
    – FreeMan
    Dec 18, 2023 at 13:03
  • Is having a sensor dimmer inside the closet with a wired remote outside the closet acceptable, and what wires are available at each of the switch boxes? Dec 19, 2023 at 2:52

1 Answer 1

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This is a great design for retrofit applications, including 3-way switches. The way it works is:

  • It uses ground (legitimately) instead of neutral to power itself. That allows it to work in either end of a 3-way switch installation or in an old switch loop that doesn't have neutral.
  • It does not use a 2nd 3-way switch in the traditional way. Instead it always sends power through one (former) traveler and uses the other traveler as a signal to indicate when the switch has been toggled.
  • If the motion sensor is the "first" 3-way switch then the second 3-way switch is for signaling only and does not carry power to the light. If the motion sensor is the "second" 3-way switch then if the first 3-way switch is a dimmer the power to the motion sensor will be messed up and the motion sensor will probably not work reliably.

The result of all this is that the second switch must be either:

  • A traditional "dumb" 3-way switch, with no dimmer, motion, timer, indicator light, etc.

or

  • A standard toggle switch (on/off, not 3-way). That will actually work just fine, though the ON/OFF indicator embossed (usually, on non-Decora toggle switches) on it will be meaningless.

So how do you connect a dimmer? Probably by getting a different type of switch that is designed to work with a motion sensor, possibly a different line of "smart switches". The problem is that the dimmer needs to do two different things:

  • Dimming. This can be done by installing it after the motion sensor, not as a 3-way switch but simply as another piece in the path of the switched hot wire. This is not necessarily that hard to do. However, if you do this then if you turn the dimmer off the motion sensor will be unable to turn it on. So that won't work. You can't put the dimmer before the motion sensor because then the motion sensor won't work properly (the dimmer affects the power supply, which won't work well with the motion sensor). And as you already know, you can't put it in the usual 3-way setup.
  • 3-way on/off. This can be done by installing as you did. But then the dimming doesn't work because the power for the light is not actually flowing through the dimmer but just acting as a signal mechanism to the motion sensor switch.

So you really can't get "there" from "here". Without something entirely different.

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