How does a wall switch work?

Question

This might be a simple question… but I’m not sure how exactly a wall switch works:

Let say there is a living room with 2 wall switches (switch A and switch B), both controlling the same light fixture. Currently both switches have their handles flipped down. Now I walk to switch A and flip the handle up, and the light fixture comes ON. Then I walk to switch B and flip the handle up, and the light fixture turns OFF. Finally I walk back to switch A and flip the handle back down, and the light comes ON… How is this possible?? I thought a wall switch is always “up is ON and down is OFF” (or vice versa). But according to the above example switch A can be ON when the switch is up / down, depending on what the other switch did previously… So technically the switches only “change state” when flipped to the opposite direction, instead of opening / closing the contact?? … How does this happen mechanically? So the circuit is neither in series or in parallel??

Answer 1

What your describing is a three way switch. Rather than explaining how it works I will direct you to How Stuff Works at the following link. Lets face it they have nifty little pictures and animations that will probably make it clearer than a written explanation here:

http://home.howstuffworks.com/three-way.htm

Answer 2

Those are "three way switches." Technically they are each single pole double throw configuration. One center contact has the hot wire, the other center contact has the lamp and the two end contacts have wires interconnecting them. When you have the handles flipped so that both switches are connecting themselves to the same wire current can flow.

Here is a link to site that shows an animated explanation of the conenctions and why the lamp goes on.

Answer 3

These are three way switches. They have travelers to so provide power to and from each switch no matter what position it is in.

Answer 4

You have some good answers but I thought you might enjoy seeing the switches "in action". This is a great web site:
http://www.selfhelpandmore.com/switchoutlet/3way/

Answer 5

IT IS EASY BUT YOU SHOULD BE CLEAR IF YOU WANT TO MOVE IT UNDER THE WALL OR JUST ON THE WALL?

Answer 6

It's 2 double-pole switches in series with the light -

HOT
....|
Light
....|
...0....SW1 com
../
0.....0....SW1 up, dn
.|......|
0.....0...SW2 up, dn
..\
...0.....SW2 com
...|
NEU

(Ignore the periods)