How to Wire a 4-Way Light Switch, With Wiring Diagram
Uses Of 4 Way Switches
4 way switches are always wired in conjunction 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 controlling the same light fixture. 4 way switches are only used when there are 3 or more light switches controlling one light fixture. Additional light fixtures do not require additional switches as long as they are intended to all come on at the same time.
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.
4 Way Switch
Proper electrical safety cannot be emphasized enough. As a professional electrician one of these nifty voltage detectors shown below is always in my pocket when on the job. Without need to ever touch, or even see, a bare wire they are every electricians friend and you are strongly urged to use one, or use some other method of verifying that there is no voltage on the wires you will be working on. While the 120 volts on a US lighting circuit won't kill you, being shocked is no fun at all.
Non Contact Voltage Detector from Amazon
Replacing a 4 Way Switch
Begin your task by turning off the power. Make absolutely sure the power is turned off before proceeding. Turn the light on and turn breakers off or remove fuses one at a time until the light goes off. It's a good idea to apply a piece of tape over the breaker handle; a second person, trying to turn the circuit back on to restore lights in a different room, will realize there is a reason for it being off and not flip it back on while you're working on the circuit.
Remove the two screws in the cover plate and set them aside along with the cover. There are two more screws holding the switch in place; unscrew those and set them aside as well. Grasp the switch by the "ears" at the top and bottom and gently pull it out of the electrical box, being careful not to touch the wires on the sides. Good electrical safety practices dictate here that a voltmeter be used to double check that the circuit is actually off; either use a non-contact voltage detector or a volt meter with one probe to each of the side terminals (one at a time) while the other is touched to the green ground screw near one end of the switch. You may have turned off the wrong breaker, the light bulb may have burned out while you were away at the breaker panel or someone else may have turned it back on. Make sure that the circuit is dead before continuing or touching any bare wire.
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 will probably 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 - there is no reason to disturb them at all unless you wish to simply verify that the connections are firm.
Remove the wires from their terminations on the switch. If the wires are under the side screws, loosen those screws (they cannot be completely removed) and bend the wire from under the screw. If the wires are pushed into a small hole in the back of the switch, insert a small screwdriver or other tool into the slot next to them; this will release the spring tension and allow the wires to be pulled out of the hold. Occasionally they are frozen into place after years of use; if this happens cut the wire as close to the switch as possible and strip about 1/2" of insulation from the end of the wire for use with the new switch.
Fold the wires that were on the top of the switch up and out of the box, and the wires that were on the bottom down and out of the box. This will be a reminder of where they are to be terminated on the new switch, but if they get disturbed and you can't tell where they go, find where each wire comes from. Although there may be two multi-wire cables entering the box through the same hole in the electrical box, 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. The last wire will be either green or, more commonly, completely bare of insulation. This wire goes to the green screw located near the end of the switch and is the ground wire. Modern electrical codes require this wire at every switch, but older homes may not have it; if it is missing from your box, just leave that green screw empty.
While it is quick and easy to simply push the wires into the new switch, and most electricians do that in the interest of saving time, it is preferable to put them under the screws as the springs in the holes will loosen over the years and make a poor connection. Using needle nose pliers or other tool, bend the bare end of the wire into a small circle, loosen the screws as far as they will go, and work the wire under the screw head and around the screw in a clockwise manner (if put on backwards tightening the screw will tend to "unbend" the wire and it may come away from the screw). Firmly tighten the screw and repeat for each wire. Terminate the ground wire onto the ground screw if there is a ground wire present in the box.
Insert the switch back into the box, neatly folding the wires as you do so. Try to keep all the wires behind the switch, not alongside it. Fasten the switch with the two screws provided, refit the cover plate using the same screws that you carefully saved, and you're done.
3 Way and 4 Way Switch Wiring Diagrams
Wiring a New 4 Way Switch
At the risk of being repetitious, make sure the power is off before making any connections to an existing circuit. While some of the work being done will be with wires that cannot be carrying power yet, there must come a time when connections are made to what could be "hot" wires - be absolutely sure that that circuit is dead.
For those readers that will be installing a whole new circuit, and are unfamiliar with physically getting wire from one place to another, an article on how to add an outlet contains valuable tips and instructions on the process. The process of pulling wire through walls, ceilings and attics is the same whether for lights or receptacles.
The two wiring diagrams above are of a 3 way switch setup and the same basic setup with a 4 way light switch added. 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. If you are not familiar with 3 way switches the link given near the top may be valuable and is suggested reading.
While other methods of physically getting the necessary wires to each switch are possible (see the article on wiring three way switches), the 2011 National Electric Code, article 404.2.C, was changed to require a "neutral" (white) wire at each switch location whether it is actually used or not. In general practice the diagram above is most often used, and is a good guide for wiring a new 4 way switch circuit.
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 above; 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 and terminate the traveler wires on the 4 way switch while making sure that there is a neutral in each box. Be careful here - some of those diagrams make it nearly impossible to have the neutral wire in the box and were included for those people working on older homes. New work, as opposed to simply replacing a switch, must have the neutral wire in every switch box. 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.
Using the diagram shown here a two wire Romex cable (black and white wires) is used to provide power to the first switch. From there, 3 wire cables (black, white and red) are used between the switches, with a final 2 wire cable going from the last switch to the light fixture. As can be seen, the neutral from the power in cable simply passes through each electrical box, splicing as necessary, and ends up in the light fixture; in this manner the NEC code is satisfied with a neutral in each box.
When terminating the wires on the individual switches, the first, 3 way, switch has the black "power in" wire terminated on the "common" terminal (the screw is a slightly different color from the two traveler screws) and two "traveler" wires (black and red from the 3 wire cable) on the other two terminals. Plus, of course, a ground wire - ground wires are "pigtailed" at each switch and terminated on the green ground screw of the switch. The white, neutral wires from both cables are spliced together with a wire nut; strip insulation from the last 1/2" and twist a wire nut on. Tug firmly on each wire while holding the nut in the other hand; if it's going to come apart much better that it does so now rather than later, back in the box where you can't see it.
The second, 4 way, switch has two traveler wires (black and red) from the first switch terminated onto the top two terminals, and two wires (again black and red) from the final, 3 way, switch terminated on the bottom two terminals. Plus the ground. The white neutral wire is again simply spliced straight through with a wire nut.
The final, 3 way, switch has the two travelers from the 4 way terminated onto the traveler terminals and the black "switch leg" from the light fixture onto the "common" terminal. Terminate the ground wire and again splice the neutral wires without terminating them anywhere.
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 to the circuit you are working on. A 20 amp switch can be used on a 15 amp circuit, but never put a 15 amp switch on a 20 amp circuit. Be careful when re-using older switches as some don't have a ground terminal; current NEC code requires that every switch be grounded.
Likewise, any new wire used must match existing wire in size. A 20 amp circuit requires 12 gauge wire (either 12-2 or 12-3) while a 15 amp circuit may use 14 gauge wire (14-2 or 14-3). 14 gauge wire is easier to handle and cheaper as well, but if you are tying into a 20 amp circuit you must use 12 gauge wire.
© 2011 Dan Harmon