I assume we all have a basic understanding of an electric circuit. You run two wires between each end of a battery, and each terminal of a lightbulb socket, and let there be light. You can add a switch in the middle of one of the wires to break the flow of electricity and now your light can be turned on and off. Chances are, you haven’t made it through science class without building this experiment yourself.
However, I found myself baffled by a light switch this past week. You probably have one of these in your house.
There’s a light in the middle of a long hallway, and a switch at either end. Both switches can turn the light off and on. I had never thought about it before, but when I did, I realized I didn’t know how it worked. This must be remedied!
A basic switch works by breaking the continuity of the wire. Just like you see in the old Frankenstein movies, when the mad scientist throws the switch, the metal terminals are now touching, and the juice flows. That’s how your basic single switch light works. It’s either on or off.
For a three-way switch there’s no such thing as on or off positions, since the result of flicking the switch is determined by the previous state of the light. Moving the switch upwards could turn it on or off depending. So, the key to understanding a three-way switch is to think of “up and down” instead of “off and on”.
In the circuit there are two wires running between the switches. Flicking the switch simply redirects the flow of electricity to either the upper wire or the lower wire.
When both switches are up, the circuit can flow along the upper wire and continue along it’s merry way to light the bulb. Same if both switches are down, the electricity flows uninterrupted along the lower wire.
However, when the switches are opposite to each other, the circuit gets broken. The first switch is sending electricity along the upper wire, but the second switch is only connected with the lower wire. The bulb cannot light.
Changing the position of either switch will align things once again to brighten your day.
So simple… once you know!
- Source: Basic Electricity – Switches
