4 Way Switch
DEAR TIM: I am pulling my hair out wiring a 4-way switch. What is the secret to 4-way switch wiring? Do you need a special 4-way electrical switch or a 4-way light switch? At this point, my new wife thinks she married a dunce. If you can teach me how to wire a 4-way switch, I will be eternally grateful. If you can't help, I will be forced to admit defeat and will call an electrician. Robert M., Ft. Collins, CO
DEAR ROBERT: Listen, don't beat yourself up too badly. There are many people who are flummoxed by the mysterious 4-way switch. I liken the 4-way switch, and its first cousin the 3-way switch, to the famous Wizard of Oz. Once you slide the curtain, you can see the Wizard is just a person. The same is true for these switches; when I slide away the plaster and drywall, you will see these switches are as simple as grade-school addition.
The first thing you need to know is that the 4-way switch is indeed a very special switch. If you look at a regular single-pole switch that controls a light or series of lights from just one location, you will see it has two screws on it plus the green ground screw. A 3-way switch has one additional screw and a 4-way switch has four screws plus the green grounding screw.
You use 4-way switches in situations where you want to control a light or other fixture from more than two locations. For example, the second-floor hallway lights in my own home are controlled at four different locations. To accomplish this, you have to have two 3-way switches and two 4-way switches.
The placement of the 4-way switch(s) in the circuit is extremely important. A 4-way switch must always be in between two 3-way switches. I know this sounds confusing, but let's see how it is done in the real world if you were to remove the drywall or plaster from your walls and ceilings.
For sake of discussion, I will describe the simplest and most straightforward manner I know how to wire a circuit with a 4-way switch. We would start the job by nailing up three electrical boxes to the wall studs. This circuit will have the mandatory 3-way switches and the single 4-way switch. Let's number the electrical boxes 1, 2 and 3 and make the assumption they would be in a line as if the switches were in a very long hallway.
The number 1 box would be at the one end of the hallway and into it would feed the power from a cable that contains a white neutral wire, a black continuous-hot wire and the bare ground wire. This continuous-hot wire is controlled by a circuit breaker or fuse.
A second cable leaves the number 1 box and proceeds to the number 2 box in the middle of the hallway. This cable has four wires in it; white, black, red and bare copper. A second cable that contains these same four wires leaves the number 2 box and goes to the number 3 box at the far end of the hallway. A final cable leaves the number 3 box and goes to the light fixture we are trying to control. This final cable is like the first one we installed in the number 1 box; it has just a white, black and bare copper wire.
In all three boxes, you connect the white wires to each other with a wire nut. You do the same with the bare copper wires and create a tailpiece of bare copper that connects to the green grounding screw on each switch. In each box you are left with black and red wires. These connect to the terminal screws on the switches.
Since you are just concerned with the 4-way switch, look at the actual switch. Hold it up as if it were in the switch box. You will see two of the screws are on the bottom and two are on the top. In my example, you take the black and red wire from one of the cables and attach them to the bottom screws. It doesn't matter which ones. Then you take the red and black wires from the other cable and attach them to the top screws of the 4-way switch. Once again, it doesn't matter which color wire goes on which screw. Assuming you did not take apart the 3-way switches in your circuit, your 4-way switch will now work perfectly.
You can have many 4-way switches in a circuit. As crazy as this sounds, you could have 10 switches control one light. This circuit would have the mandatory two 3-way switches and eight 4-way switches.
To make any of these circuits work correctly, you must connect the wires to the right screws on the 3-way switches. Look closely at the 3-way switches. They will have a black screw and two brass ones. Connect the black continuous-hot wire in box number 1 and the black wire that goes up to the light fixture in box number 3 to the special black screw on each 3-way switch. The remaining two wires at each box connect to the brass screws on the 3-way switch.