How To Wire A 4 Way Light Switch, With Wiring Diagram

4 way switches are always wired in conjuction with two 3 way switches. That is to say that any time you find a 4 way switch there will also be two 3 way switches also controlling the same light fixture.  4 way switches are only used when there are 3 or more light switches controlling one light fixture.

Each such lighting circuit will contain two 3 way switches and one or more 4 way switches (the number of 4 way switches that may be used in such a switching configuration is unlimited).

Because there will always be 3 way switches present it is necessary to understand how to wire a 3 way switch before attempting to understand and use a 4 way switch. If you are doing anything more than simply replacing a defective 4 way switch please examine the link on how to wire a 3 way switch before proceeding; it will open in a new window that will return the reader here when it is closed. If, on the other hand, you are simply replacing a 4 way switch in an existing circuit the next section will address that simpler task.

If you are simply replacing an existing 4 way light switch, please begin by reading this article on how to replace a switch; it covers the basics of replacing any light switch. In any case, make absolutely sure the power is turned off before proceeding.

There are four wires that are terminated (fastened to) a 4 way switch, plus the green or bare ground wire. In nearly every case these wires will enter the wall box in 2 separate cables. These cables may well contain at least one more wire each, but these extra wires are simply spliced together in the wall box and do not terminate on the switch.

If you have not marked the cables as to where they go, find where each wire comes from. Although there may be two multi-wire cables entering the box through the same hole, you will find two wires in each cable that go to the switch. Two wires from one cable will terminate to the top two screws (it doesn't matter which of the top two screws is used for which wire) and two from the other cable will terminate on the bottom two screws. If you are unsure how to actually connect the wires (or disconnect them from the old switch) please check out the link above; specific directions are given there. Always connect the green or bare ground wire to the green ground screw on the switch.

Whenever work is done on electrical circuits, make sure the power is turned off. Turn the light on and turn breakers off or remove fuses until the light goes out. An additional check with a non contact voltage tester is a very good additional check and can't hurt.

The two wiring diagrams to the right are of a 3 way switch setup and the same basic setup with a 4 way light switch added (click a diagram to expand it to full size). While the physical location of the 4 way switch may be anywhere, the electrical location of the switch is always between the two 3 way switches. If additional 4 way switches are needed, they will also go between the 3 way switches. Electrically, the 3 way switches are always the first and last in the line of switches.

When wiring in the 4 way switch it is most simply described as simply cutting the two traveler wires (the two wires that go between the two 3 way switches and terminate on each switch) and putting two wires from one switch on the top two terminals of the 4 way switch while putting the other two wires from the other switch on the bottom two terminals.

The first of the two diagrams is taken directly from the article referenced at the top of this hub on how to wire a 3 way switch; the second is merely that same diagram expanded to allow the addition of a 4 way switch in the center. Each of the diagrams in the 3 way switch article can be treated the same way; merely add the 4 way switch between the other two while terminating the traveler wires on the 4 way switch. Any extra wires passing between the two switches (normally one more wire) is simply spliced in the 4 way switch box to continue on uninterrupted. Make sure that the green or bare ground wire is always pigtailed out and terminated on all switches.

A final word of caution; when buying switches, make sure the switch amperage is rated at least as much as the breaker that turns off the power.  A 20 amp switch can be used on a 15 amp circuit, but never put a 15 amp switch on a 20 amp circuit.