What do I do with this "extra" black wire on my existing switches to replace them with two Kasa smart dimming switches?

EXISTING SWITCH: enter image description here

EXISTING SWITCH EXPOSED: enter image description here

NEW SWITCH (I have two of them):

enter image description here


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FULL POST: Bought my first house last month, and I've been making modifications. I've installed a smart doorbell, smart lock, new cabinets hinges & pulls, etc.

DYI skills: 5/10

Electrical skills: 2/10

Based on what I read: white is neutral, copper/green is ground, red is load, and black is line. But I have an "extra" black line connecting the existing switches (I think). If that's what's going on, how do approach installing two smart switches to replace the two existing switches? I don't see where I can connect an extra black wire.

If I bought the wrong switches, can you send a link or two for better ones?

Please and thank you!

  • Are the old switches individual switches or 3-way switches (where there is a second switch for each one - e.g., at the other end of the room or up or down a staircase) Can you show pictures of the other side of the switches? Sep 3, 2023 at 18:55
  • Neutral must be white, but white might be something also(hot, a second hot, traveller).
    – crip659
    Sep 3, 2023 at 18:55
  • Please post the Kasa part number. They have several different products in this lineup. Sep 3, 2023 at 19:21
  • @manassehkatz-Moving2Codidact I believe so. For the existing living room switch I shown, the left side is for the kitchen, the right side is for the living room. And there is another set of switches in the kitchen that controls the exact same rooms. Two sets of switches that controls the same lights.
    – chadp
    Sep 3, 2023 at 19:35
  • @RobertChapin Kasa model number: HS220 amazon.com/dp/…
    – chadp
    Sep 3, 2023 at 19:35

2 Answers 2


From comments: Two sets of switches that controls the same lights

These are 3-way switches. A traditional (i.e., not "smart") 3-way switch has 3 wires (ignoring ground):

  • Common
  • 2 Travelers

The common can either be hot (i.e., from the breaker) or switched hot (i.e., to the light). A 3-wire (ignoring ground) cable goes between the switches, including the two travelers and hot, switched hot or neutral.

Each of the existing switches has a common black wire (which may be hot or may be switched hot, can't tell without more information) and black and red travelers. Those travelers go together in a cable, along with a white wire, to the other switch in each pair.

The Kasa HS220 is for single switches. For 3-way switches you need the KS230 Kit:


  • Thank you for the elementary school lesson! And yes, the term "three way" was not intuitive - even though it should've been - it's the number of wires. Thanks
    – chadp
    Sep 3, 2023 at 20:41
  • 2
    Biggest thing to remember about US wiring: wire counts don't include ground. You always need ground, but you never count it. So a "2 wire" or "/2" cable is black/white/ground, a "3 wire" or "/3" cable is black/white/red/ground. Sep 3, 2023 at 20:49

Your original switches are three way, indicated by the traveller (red wire). One black wire is coming in from the power source (labeled load), and the other is going out to the device (line). Additionally, there should be a white "neutral wire" on both of those cables connected to each other and pushes to the back if the box. Sometimes in older houses they took some shortcuts and that neutral is missing...in which case you have a much larger job than you may want. Neutral is required to maintain power to the smart outlet to be functional.

Assuming you have neutral wires in this box, you will need to pay attention to which is which and connect to two black wires to load and line on the new switch. Connect the ground (bare, green, or paper wrapped) wire. Then connect a small length of wire from the existing neutral connection to the neutral terminal.

Your switch may support just hooking the red traveller up and using the existing switch but you will need to read instructions to be sure. If not, cap the red wire in this box and uninstall the other switches and cap their wiring as well. Or repeat and install the appropriate add on switches for this brand.

  • Things are sometimes different with smart switches. But with traditional switches you have two travelers and then one other wire, which can be line (hot) or load (switched hot). Sep 3, 2023 at 20:06

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