Understanding 3-Way And 4-Way Switches
You’ve you’ve a room that has two or more entrances and you want to have a switch at each entrance to regulate a light? Or more commonly, did your electrician set one up for you and now you have replaced a broken switch but cannot 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 distinct purpose. Two-way switches are most typical and only have two terminals along with the bottom screw. These are very simple in nature and simply either break or complete the circuit to show a light on or off.
When you’ve got two switches that control a light, you could use 3-way switches (more on 4-ways later if you have more than 2 switches). Usually we see people get in trouble once they want to replace one switch with a dimmer. The dimmer in this situation must be a 3 way and the three wires must go to the proper terminals. (at the end of this article we explain how to have a look at a switch and more often than not get the hook-up correct. When all else fails, use a continuity tester.) Three-way switches could have 3 terminals in addition to the bottom 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 may 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’ve got 3 or more switches to manage a light. As may be seen in the diagrams below, there may be always a 3-way switch at the beginning and end of the circuit, with 1 or more 4-ways in between. The 4-way switches simply have the two travelers coming in after which going out to the following switch down the line.
Let’s take a look a some diagrams to grasp how the circuit and switches work.
First here is an example of a 3-way switch setup. Light is off as there isn’t any path for the hot.
—- —- OFF
—-|1 | | 1|—-| Light |
| 3|——-+3 / | ——-
—- —- Neutral|
Switch 2 is moved, Light is ON as there’s now a path for the new.
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 have to be in-between the three-ways.
—- —- —- 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 isn’t any path and thus the light goes off.
You could add additional 4-way switches into the middle of the wiring. The three-way switches must always be in the beginning and at the tip of the circuit.
The wires in-between the the 3-way switches are called travelers. If you are pulling wire through conduit, best to make use of different colored wire like blue and orange. In case you are using Romex, I prefer to make use of 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 to not wrap a black piece of tape across the white wire to mark it as a hot.
So use the red and the black to your travelers between switches. On the 3-way switches, you cannot just connect the new to one of the terminals and the travelers to the remaining two. Have a look at a diagram on the switch or most times there’s a single terminal on the highest or bottom for the in/out hot and then two terminals (one on each side) at the opposite end are for the travelers. Connecting the new to the side that has one terminal and the travelers to the side that has two terminals is usually NOT the option to do it.
Same goes for the travelers in and out of a 4-way switch. The in is typically both sides of the highest of the switch and the out goes on both side of the underside of the switch. You can verify what is right or wrong using a simple continuity buzzer and comparing the outcomes against the diagram above.
In the event you did not get the wires on the proper terminals, then you will see that that it sometimes takes flipping two of the switches to get the light to turn on or off. With the correct wiring, any single switch that’s flipped should cause the light to go on or off.
And please remember to show the facility off first. BZZZT sounds or arc welding your switch is not an excellent thing.