I'm trying to automate light switches, but struggling to understand the way my switches were installed. Electric eng. is obviously not my field, but I've researched 3-way switches, so I have a basic understanding of how they work (line + travelers + output).

The set-up has three circuits:

  • Circuit A is controlled from both panels with 3-way switches
  • Circuit B is controlled from both panels with 3-way switches
  • Circuit C is controlled from one panel with 2-way switch

The top-left connector on each switch is L, and the two bottom connectors are marked as 1 and 2, I assume for the travelers. It's an older building, so there is no neutral.

My question: I can't wrap my head around how this works with wires connecting one circuit to the other. Looking for someone to shed some light on this type of set-up.

wiring in both pannels

  • Building with no neutral? Are you sure you want to DIY this? In some countries it is illegal to work on residential building installations yourself - unless you are a legalized electrician (In which case you would not be asking this).
    – Justme
    Commented May 11 at 21:09
  • Many automation packages simplify all these via microprocessors boiling everything to a "change" command.
    – Abel
    Commented May 11 at 22:21
  • 1
    @jsotola really? In my area, 3-way switches are those that let you control one fixture from two different locations. They're even advertised as such.
    – Javo
    Commented May 11 at 23:15
  • 1
    You have two wires marked green. Green is only for ground and should not be connected to anything really except metal boxes/green screws. At least you know enough that neutral is white, but white does not mean neutral.
    – crip659
    Commented May 11 at 23:54
  • @crip659 I assume they used the wrong wire colors when installing. Which is why I wanted help to decipher this set-up. "C" controls one fixture, and only has two wires connected, green and red, so green hast to be powered when ON.
    – Javo
    Commented May 12 at 0:32

1 Answer 1


The set-up has three circuits.

You're likely confusing switches for circuits. Unless you have DC power transmission, some or all of these light switches are wired in parallel on the same circuit. Nothing in the diagram suggests three separate circuits.

Circuit C is controlled from one panel with 2-way switch

All the switches in the diagram look the same. Are we talking about a 2-way switch or a 3-way switch?

The top-left connector on each switch is L

Are you sure? This can be an easy mistake, looking at one switch and assuming the other four have identical part numbers.

It's an older building, so there is no neutral.

Neutral wires are almost never switched. This is unrelated to the age of the building. Except, the very latest code changes require an extra neutral wire even where it's unused.

Wires are represented in their actual colors.

Green wires are never allowed on ungrounded terminals in the USA. Which country are we talking about here?

In general, where the switches are connected to one another, with more than one wire, one of three things has happened:

  1. The diagram was incorrect?
  2. The switches were installed wrong?
  3. Someone designed a convoluted multi-switch circuit that was unlikely to be useful to anyone else?

You could functionally check these by turning the lights on and off in various combinations and deciding if the switches work as expected.

The way the diagram is drawn, most of these switches don't even have 2 travelers connected, and couldn't function as a normal 3-way.

  • Thanks for taking the time. That's why I'm surprised it works as intended. If I activate either of the switches labeled "A", one section of fixtures turns on; if I activate either of the "B" switches, the second section turns on; if I activate the "C" switch (the only 2-way switch here), the third section turns on. And I can't understand why A, B and C behave completely independent of eachother if their switches are connected. FWIW, this is a building in Mexico.
    – Javo
    Commented May 12 at 5:16
  • @Javo Mexico does not allow green except as ground, but might explain green being used if not inspected and done by someone not knowing.
    – crip659
    Commented May 12 at 10:30
  • If you're sure the switches are working, then you have a bad diagram. Maybe a misunderstanding of how the wires are spliced in other parts of the system. Commented May 12 at 17:04
  • @RobertChapin I just double-checked against the photos I took of the backs of the switches, and the diagram is correct. I think what is misleading here is that the wire colors were used incorrectly and there may be strange slicing in parts of the system I can't see.
    – Javo
    Commented May 12 at 19:26
  • @crip659 agreed, I'm just representing the color I see in the wires, I think it's clear that whoever installed the wiring used incorrect coloring.
    – Javo
    Commented May 12 at 19:28

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