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I recently bought a house and the 3 switches controlling one light fixture aren't working properly.

Here is a diagram of the three 3-way switches and wires: enter image description here

  1. The first thing that comes to mind is: there is no 4-way switch! Is it possible to do this without one?
  2. When I disconnected all the wires from the switches and turned on the breaker, I found something strange in the AC voltage measurements:
    • Switch 1: White(30), Black(0), Red(34)
    • Switch 2: White(52), Red(34), Red(34)
    • Switch 3: White(52), Black(120), Red(34).

With those measurements, it is not clear to me how to determine which wires are travelers, although I suspect that Switch 3's black wire is coming from the main panel.

In the switches, green is ground terminal, black is common.

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There is such a thing as a "4-way switch". A three-way is SPDT, used to select between the two travelers. A four-way is DPDT, sitting in the middle, wired to either pass the travelers straight through or exchange them. You can have as many 4-ways interrupting the travelers as you like, since only their net result (swap or don't swap) affects the final result.

enter image description here

Colors for clarity; your colors will of course be different.

Your sketch shows only one cable (or conduit) with three conductors (not counting ground) coming into each switch box. If that's true, (a) you are dealing with switch loops (see past answers), and (II) the one to the four-way switch (to swap travelers) needs to have four conductors (plus ground), not three, otherwise you can't have full control at all points.

If there are more cables or conductors coming into one or more of the boxes, we need details of that. Photos of the switches as currently wired, showing the inside of the box too so we could see which cable they were connected to, would help a lot.

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  • does this mean that a SPDT in the middle can either "close" or "open" the circuit, meaning that an SPDT in the middle is NOT ok to use in my case?
    – fingia
    Commented Feb 26 at 19:25
  • Yes, it means you need a DPDT in the middle to get the behavior you want. Or smart switches linked at the data level.
    – keshlam
    Commented Feb 26 at 19:29
  • With three 3-ways, the best you can do is making one switch enable or disable one of both of the others. Even with a "wire-or" circuit. If you're trying to fix an existing installation without running new wire, and don't have the wires you need, see past answers about using smart switches to control each other
    – keshlam
    Commented Feb 26 at 19:37
  • What if I wanted to simply remove switch 3 from its electrical box, given the voltage measurements, what are the proper connections for switch 1 and 2? The idea being that at last I can control the load with switch 1 and 2.
    – fingia
    Commented Feb 26 at 20:26
  • Question behind the question: what's wrong with just removing that switch, splicing the two wires it connects to each other when the other switches do what you want (using whatever approved connector is available in your country; I'd grab wire nuts), insulate any other exposed wires, put a blank plate on the box, paying the plate to match the wall, and call it done? Yes, it would be better to fully analyze this. But you haven't given us enough information to do so, and the practice "splice past it" solution might still be the simplest answer, depending on exactly how this was wired
    – keshlam
    Commented Feb 27 at 1:47

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