I think I have a regular 2-way Switch but there are 3 wires connected to it: 2 black wires going to the same screw and a red one going to an upper one. I'm not sure which wire is doing what. How can I identify or know which wire is which? The new switch I have is a smart switch and it's asking me for 2 live, 1 ground, and 1 neutral. Inside the box I could find the neutral wire and also a copper wire, but I don't know the others.

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I'm guessing here, so you'll need to investigate and verify.

The black that loops over the screw is your constant hot, and it travels on to supply the other switch or some other part of the circuit. The red is the switched hot to the light. The whites are neutrals, one of which comes back from the light. Bare copper is ground.

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  • The answer sounds good to me. That's the normal way to do it.+ – Ed Beal Dec 18 '18 at 14:34

The 2 wires on 1 screw have the same purpose; they are simply using the screw terminal as a splice. They are joining 3 things: the supply hot, supply onward to some other load, and supply to the switch itself. I'm saying "supply" because 99% of the time when you see 2 wires on one switch terminal, that is what's going on.

This is one of several legal wiring methods to do that: If a switch did not support that, you would use a short black wire from the switch, and join that with those other two wires in a wire nut or splice bar. If this smart switch comes with a pigtail, this is exactly how you would do that.

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