Do you have a room that has two or more entrances and you would like to have a switch at each entrance to control a light? Or more commonly, did your electrician set one up for you and now you have replaced a broken switch but can not get it to work right? Fear not, some simple diagrams should help sort it out.
First of all, there are 2-way, 3-way, and 4-way switches; each with a different purpose. Two-way switches are most common and only have two terminals in addition to the ground screw. These are very simple in nature and simply either break or complete the circuit to turn a light on or off.
If you have two switches that control a light, you must use 3-way switches (more on 4-ways later if you have more than 2 switches). Usually we see people get in trouble when they want to replace one switch with a dimmer. The dimmer in this situation must be a three way and the three wires must go to the correct terminals. (At the end of this article we explain how to look at a switch and most of the time get the hook-up correct. When all else fails, use a continuity tester.) Three-way switches will have 3 terminals in addition to the ground screw. One hot (usually black) wire either comes from the power panel into the switch or one hot wire exits the switch and goes to the light. In between the switches are two wires called travelers. These are considered switched hot wires and can be typically black, red, or sometimes a white wire has black tape wrapped around it at each end to designate it as a hot and not a neutral wire.
Four way switches are used when you have 3 or more switches to control a light. As can be seen in the diagrams below, there is always a 3-way switch at the start and end of the circuit, with 1 or more 4-ways in between. The 4-way switches simply have the two travelers coming in and then going out to the next switch down the line.
Let's take a look a some diagrams to understand how the circuit and switches work.
First here is an example of a 3-way switch setup. Light is off as there is no path for the hot.
Switch 1 Switch 2
—- —- OFF
Hot | / 2 | ——- + 2 | ——-
—- | 1 | | 1 | —- | Light |
| 3 | ——- + 3 / | ——-
—- —- Neutral |
——————————–
Switch 2 is moved, Light is ON as there is now a path for the hot.
Switch 1 Switch 2
—- —- ON
Hot | / 2 | ——- + 2 | ——-
—- | 1 | | 1 | —– | Light |
| 3 | ——- + 3 | ——-
—- —- Neutral |
——————————–
Either moving Switch 1 or Switch 2 will break the hot. And from the Off state, either Switch will make the connection.
Now for an example of a 4-way switch setup. The 4-way switch must be in-between the 3-ways.
3-way 4-way 3-way
Switch 1 Switch 2 Switch 3
—- —- —- ON
Hot | / 2 | —– | 1–3 | —– | 2 | ——-
—- | 1 | | | | 1 | —– | Light |
| 3 | —– | 2–4 | —– | 3 | ——-
—- —- —- Neutral |
—————————————–
Moving either switch 1 or 3 like before will turn the light off.
3-way 4-way 3-way
Switch 1 Switch 2 Switch 3
—- —– —- OFF
Hot | / 2 | —– | 1 3 | —– | 2 | ——-
—- | 1 | | X | | 1 | —– | Light |
| 3 | —– | 2 4 | —– | 3 | ——-
—- —– —- Neutral |
——————————————
Switch 2 either connects 1to3 and 2to4 like shown or when it is flipped it cross connects 1to4 and 2to3. So in the case shown, if switch 2 was flipped, the path would go from switch 1 1-2, then switch 2 1to4, but would stop a switch 3 since there is no path and thus the light goes off.
You may add additional 4-way switches into the middle of the wiring. The 3-way switches must always be at the beginning and at the end of the circuit.
The wires in-between the the 3-way switches are called travelers. If you are pulling wire through conduit, best to use different colored wire like blue and orange. If you are using Romex, I prefer to use the 4 wire version which has a ground, a white neutral, and a black and a red. Little more expensive but from a safety perspective I prefer not to wrap a black piece of tape around the white wire to mark it as a hot.
So use the red and the black for your travelers between switches. On the 3-way switches, you can not just connect the hot to one of the terminals and the travelers to the remaining two. Look at a diagram on the switch or most times there is a single terminal on the top or bottom for the in / out hot and then two terminals (one on each side) at the other end are for the travelers. Connecting the hot to the side that has one terminal and the travelers to the side that has two terminals is usually NOT the way to do it.
Same goes for the travelers in and out of a 4-way switch. The in is typically both sides of the top of the switch and the out goes on both side of the bottom of the switch. You can verify what is right or wrong using a simple continuity buzzer and comparing the results against the diagram above.
If you did not get the wires on the correct terminals, then you will find that it sometimes takes flipping two of the switches to get the light to turn on or off. With the proper wiring, any single switch that is flipped should cause the light to go on or off.
And please remember to turn the power off first. BZZZT sounds or arc welding your switch is not a good thing.