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I’m trying to replace my bedroom light switch with a smart switch but it’s not working like I would expect.

It’s a single pole, 4 wire switch wired to a split outlet. After installing the smart switch, the switch only gets power if something (a floor lamp with a bulb) is plugged into the outlet. At the switch, there’s 50v between live and load when the switch is off and a 0v when the switch is on. 18v between load and neutral and ground when off, 120v when on. Constant 120v between live and neutral and ground.

Bulb types act differently and affect voltage at the outlet differently. Incandescent does nothing. 0v between live and everything on or off. CFL flickers when off and flickers more quickly when on. Fluctuates between 45v and 60v when off and between 55v and 60v when on. LED does nothing. 2-3v when off, 4-5v when on.

I’ve tried 2 floor lamps and 2 smart switch brands. The first switch I couldn’t even get to the WiFi setup. Pushing the power button on the switch did nothing. Got different errors each time I reset the breaker. The second switch setup and functions just fine, but the light functions as described above. If I use the original (non-smart) switch and a smart outlet, it functions fine. I guess I don’t understand why the smart switch wouldn’t function exactly like the smart outlet.

The switch I’m working with is a Kasa HS200.

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  • Don't measure voltage from live to load. This is meaningless. Voltmeters must be used in parallel with flow of current. Only measure one wire to the other, preferably hot to ground. Commented Oct 16, 2022 at 19:34
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    Your symptoms clearly indicate that you’ve placed the switch hot or neutral in serirs with the outlet. The switch is getting power through the light you plugged in. Please edit your post to add photographs of the switch wiring.
    – DoxyLover
    Commented Oct 16, 2022 at 19:50
  • Can you post photos of the inside of the switch box in question please? Commented Oct 16, 2022 at 20:19
  • Images added to post.
    – Shane L
    Commented Oct 16, 2022 at 21:11
  • Thanks for the live to load advise. The measurements for the outlet were live to everything else. The values were identical when measuring live to load, live to neutral, and live to ground.
    – Shane L
    Commented Oct 16, 2022 at 21:17

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There are no "4 wire single pole" switches. A single pole switch has two main wires (hot and switched hot, or line and load), and possible a 3rd wire for ground. So "4 wire" indicates that either there is a 3-way or 4-way switch involved or that some additional wires that happen to be attached to the switch are being counted.

A smart switch, generally speaking, will need hot, switched hot (and it may matter which is which, unlike a simple switch where they are can be reversed with no effect) neutral and possibly ground. A smart switch may also include an additional optional wire for use a in a 3-way configuration, rather than having two separate SKUs.

In addition, colors are nearly meaningless in US wiring, except that green (or bare) is always ground. But while neutral is almost always white, white is not necessarily neutral, particularly with switch loops (which you may have here) and 3-way switches.

Sorry, can't provide more of a solution without more details. The starting point is to figure out where each wire is coming from. You likely have either one cable (if "4 wire" includes ground) or two cables (if "4 wire" excludes ground), and knowing where each cable goes and how each black, white and (if applicable) red wire is connected on the other end will determine what to do at the switch.

It is actually quite possible that you do not have neutral in this location, in which case a different switch (or new cabling) may be needed.

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    I’m stupid, but you already know that. This outlet is controlled by 2 switches so it looks like I’ll need a 3 way switch. The other switch is hidden behind a curtain. I never use it nor see it so never thought about it.
    – Shane L
    Commented Oct 16, 2022 at 21:55
  • After getting a 3 way switch, that solved the issue. The switch as pictured above did not have a neutral so I had to replace the other switch which fortunately did have a neutral. The other switch however has 2 switches and now the faceplate doesn’t line up, but that a separate issue.
    – Shane L
    Commented Oct 21, 2022 at 21:35

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