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I'm working on replacing the dimmer switches in my house with smart dimmer switches and have run into a wiring issue. I've installed 2 Kasa HS 220 smart dimmer light switches so far, but when I went to pull the third regular dimmer switch out to begin installing the third, the switch had 1 black wire and 1 white wire connected to the switch, and a ground wire on the back of the panel.

The Kasa devices have four connections for: Load, Line, Ground, and Neutral so I'm not sure if this third switch will work. So far, I've found that with the circuit on, the white wire is always hot, but the black wire is only hot when the light switch it turned on. Has anyone come across this type of wiring setup before, and would this work for the smart dimmer switch I'm using. Here are the details for the smart dimmer switch:

https://www.tp-link.com/us/support/download/hs220/

The image below is the wiring for the current light switch.

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  • Can you post a photo of the inside of the switch box please? We need to know what wiring method was used for this to evaluate your options here...
    – ThreePhaseEel
    Mar 20, 2020 at 1:03
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    Based on just your textual description, it sounds like your current switch is wired as a "switch loop". The tl;dr version is that you only have a load (black), line (white, hopefully that has black tape around the end), and ground wire, not a neutral wire, which your smart switch requires. Once you post the picture, we'll be able to tell you what you can do about that problem in an answer.
    – Joseph Sible-Reinstate Monica
    Mar 20, 2020 at 1:23
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    I see an Anonymous User edit with pictures. Since generally anonymous random people on the internet don't magically produce pictures of other people's light switches, my guess is you signed from a different device with a new account. You should make sure to log in as JoeM for any edits or comments to your question.
    – manassehkatz-Moving 2 Codidact
    Mar 20, 2020 at 3:43
  • Can you post a clear photo that looks into the top of the switch box?
    – ThreePhaseEel
    Mar 20, 2020 at 4:00
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    Eel, I don't think there's another cable there. @manassehkatz-Moving2Codidact Yeah, it's the way StackExchange allows cookie-based accounts with no email/password. My hunch is people ask their questions from a PC, but when we ask for pix, they use a phone. Different browser, different cookie. The fix is to attach an email/password, Facebook or Google account.
    – Harper - Reinstate Monica
    Mar 20, 2020 at 5:46

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Yes, this is a classic switch loop. Nothing unusual about it (except it's new to you of course, and a darned impediment). Power (hot and neutral) from source into the lamp. The switch loop wires do exactly what you found, and there (was) no reason for neutral to make the trek down to the switch.

As of 2011, switch loops are required to bring neutral, typically using a /3 cable (black red white). Precisely to support smart switches. It is exempt if it's easy to retrofit a /3 cable.

You cannot use this switch here, unless you go into the wall and pull down a /3 cable from the lamp.

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  • Thanks for the answer! I had thought this was the case based on some reading, but wanted to get a second opinion as my experience doing anything with electrical wiring is very limited. Thanks for the advice. I'll probably take a look to see if there are other products that don't require a neutral wire.
    – JoeM
    Mar 20, 2020 at 16:28
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    @JoeM, The Lutron Caseta dimmers don't require a neutral, but they do require a working ground. They also need a hub to work, so they are a little more expensive, but I've installed 6 or 7 in my house so far and have been happy. They are also from a big company with a history of safe and certified products which would please Harper. I have an older home, so I knew I would run into the "no neutral" problem somewhere.
    – JPhi1618
    Mar 20, 2020 at 16:34

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