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.
Best Answer
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.