I have a 2-way switch connecting to a light and it works properly. When opening it up, it has 3 inputs with the same wire color. I don't know the setup and I wish to know if there is a neutral in one of them and how were they wired.

I did a simple test for "live" among the 3 wires, these are the result. by using a simple "testing screw driver" and testing on the switch

  1. When the light is off (case 1), wire 1 tested to have "live" signal, wire 2 and 3 do not have.
  2. When the light is off (case 2), wire 3 tested to have "live" signal, wire 1 and 2 do not have.
  3. When the light is on (both case), 3 of them have "live" signal.

Given the wiring diagram from Electronics Hub - How a 2 Way Switch Wiring Works?, it doesn't make sense to me.

enter image description here

How can it be and what is the setup? thank you

  • \$\begingroup\$ Comments are not for extended discussion; this conversation has been moved to chat. \$\endgroup\$
    – Voltage Spike
    Mar 20, 2021 at 14:11

2 Answers 2


A SPDT is like an XOR logic gate. The sector can only exclusively selector 1 or the other which in logic inverts the output (on/off).

For electricians, the 3 wires is related to the switch name "3-way" , for Engineers we simply them SPDT. And for students of logic an "XOR switch"...


simulate this circuit – Schematic created using CircuitLab

  • \$\begingroup\$ Second and third version senseless, because if supply and load in different junction boxes, four wire need between switches. Wasting of materials. \$\endgroup\$
    – user263983
    Mar 19, 2021 at 13:07
  • \$\begingroup\$ second case depicts what the OP is describing and satisfies the requirement of working "correctly" \$\endgroup\$ Mar 19, 2021 at 13:21
  • \$\begingroup\$ Good point @user263983 .. changes made \$\endgroup\$ Mar 19, 2021 at 13:30
  • \$\begingroup\$ Third schematic is wrong because neutral wire can not be switched or disconnected. In second connection can be made with 3 wires only if feed and load wires come into one connection box. Connection for 3-way switches is pretty standard. \$\endgroup\$
    – user263983
    Mar 19, 2021 at 17:42
  • \$\begingroup\$ 3rd is hard wired to N not switched (?). Explain contradiction on 2. It is what you said. @user263983. Or make changes you think works better \$\endgroup\$ Mar 19, 2021 at 17:47

It's a standard staircase light schematic employing two SPDT switches, one located at the foot of the stairs and the other at the head, to facilitate 'switching on' or 'switching off' of the light from either location.

The neutral is connected to one terminal of the light, with the other terminal being connected to or disconnected from the line by either of the switches.


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