# How do the lights on stairs work?

I remember that there's a very simple circuit diagram that explains how there can be 2 light switches for 1 light and that regardless of which switch you turn 'on/off' the light is toggled on/off.

This, as I recall, is the same circuit that is used for the light on a staircase where there is a switch at both the top and the bottom of the stairs.

I've been trying to draw this circuit diagram but I just can't get it... could someone explain or provide a circuit diagram to help please.

• About electricity, not electronics. Will be closed. Oct 18, 2012 at 17:12
• @BrianCarlton Please try to explain why a bit more and be a bit nicer. This comes off a bit as rude. Oct 18, 2012 at 17:40
• Ohm's law is about electricity too. Feb 15, 2016 at 17:41

In the drawn position the lamp will be on. Switching any switch will turn it off, and again any switch will turn it on again.

If you need more than two switching points you have to add "cross-switches", like this:

You have two A-type switches (for A and B) and the others are C-type.

edit
Any manufacturer of residential switching material has those cross-type switches, but in case you would ever need them in a DIY circuit with rocker switches, you can emulate them with DPDT switches. I'll leave it as an exercise for the interested reader to find out how to wire them. :-)

• C-type means a push type switch right? Oct 18, 2012 at 10:41
• @sandun - C-type will look the same as A-type, they will be indistinguishable from the outside. So if all the switches in your house are rocker type switches, then your supplier will have a C-type rocker switch as well. Oct 18, 2012 at 10:58
• @sandundhammika - The terminology for the 'C' type switches may be different in your country (in the UK they are known as 'intermediate' switches). Oct 18, 2012 at 13:30
• In the RF field, these are known as transfer switches. But we sometimes use two DPDT switches instead because that gives more isolation (and sometimes they are cheaper or more available). Oct 18, 2012 at 18:43
• @M.M At a guess, one of the two wires between the two switches is broken.
– TRiG
Dec 11, 2021 at 2:39