How to Wire a 3-Way Switch: Wiring Diagram
Wiring a 3-Way Switch
Wiring a 3-way light switch is not a difficult task... there are only three connections to be made, after all. Making them at the proper place is a little more difficult, but still within the capabilities of most homeowners, if someone shows them how. That's where understanding a wiring diagram can help.
First, what is a three-way switch?
When you want to be able to control a light from two different locations (for example, you want to be able to turn the stair lights on from both upstairs and downstairs), this is what electricians call a "three-way switch."
Is it hard to wire a 3-way switch?
To replace a switch is not difficult at all: Simply watch how you disconnect the old one and then put the wires back on the new light switch in the same position. Problems can arise when an extra switch is being added or if you forget which wire went where. That's when it becomes necessary to understand a little more about how a 3-way switch works and how to read a wiring diagram.
What do I need to know before I begin?
If you know what the purpose of each wire is, the task will become much simpler. This article will explain everything you'll need to know in order to wire a 3-way switch, with wiring diagrams and common wiring methods explained.
What about 4-way switches?
Read How to Wire a 4-Way Switch for instructions and wiring diagrams for wiring four-way switches.
How to Wire a Three-Way Switch
- Not all 3-way switches are the same. Choose which configuration you want to follow by looking at the diagrams provided below. If you're starting from scratch, Diagram #3 might be the best place to start, but these methods can be used interchangeably in old work. They merely indicate different ways to run the necessary cables.
Diagram #1 works when several light fixtures share one common breaker, and the switches are both on the same wall.
Diagram #2 works best when power is available in the ceiling but the switch boxes are on opposite walls—it is often easier to run the cable up into the ceiling light box instead of between switches.
Diagram #3 works best for cases with multiple switches in the same box, as other switches then have power available and can operate other lights without having to have a separate power in line run to them.
Diagram #4 can be useful when the light is near the first switch box. It results in lots of wires, so installing a larger box may be necessary.
- Turn off the power at your electrical panel before you begin working.
- Make sure you understand which screw terminals and which wires serve which purpose. Below, you'll find full descriptions to guide you.
- Have plenty of 14-3 type NM cable on hand, which has three insulated wires—white, black, and red—plus a bare copper ground wire. If you're connecting to 12-gauge wire, you'll use 12-3, instead.
- Follow the diagram to connect the wires (see instructions below) to the new three-way switch.
- All white wires used as travelers between the 3-way switches should have their ends wrapped with black electrical tape or in a plastic wire nut.
How a 3-Way Switch Works: Identifying the Terminal Screws
- There are three screw terminals on the sides of the switch and one on the end. Every switch has these same three terminals, but older switches might be missing the fourth ground terminal.
- The small, green screw terminal on the end is the ground terminal. It is usually painted green, although the picture does not show that color well. It can often be recognized as the screw that is part of the metal framework of the switch and is not insulated from other metal parts.
- The green or uninsulated ground wire always goes to this ground terminal. Older switches often did not have this ground terminal screw, but are no longer legal to use. Now, all light switches must have a ground terminal screw to attach the ground wire to.
- One of the three other terminals is a different color, usually darker, and is called the common terminal. Mechanically and electrically, this common terminal is connected internally to one of the other two brass screws called the traveler terminals. When the switch is flipped the other way, that connection is broken, and the common terminal is then connected to the other traveler terminal.
- The common terminal is always connected internally to one (but only one) of the traveler terminals. Which one is dependent on whether the switch is up or down.
- It should perhaps be noted that the traveler terminals are essentially interchangeable. Given that each one is to have a traveler wire attached to it, and there are two traveler wires and terminals, it doesn't matter which traveler wire goes to which traveler terminal.
Identifying the Ground, Common, and Traveler Terminals in a 3-Way Switch
Which wire is "hot"? Which screw is the "ground"?
Identifying the Screw Terminals by Color
What is the green terminal screw?
The small, green screw terminal on the bottom is the ground terminal. All new switches must have a ground, but some older ones don't.
What is the darker screw terminal?
One of the three screw terminals will be a different color, usually darker. This is the common terminal.
What are the brass screws?
The two brass screw terminals are the traveler terminals.
Identifying the Wires by Color
What is the green wire?
The green or uninsulated (copper) ground wire always goes to the ground terminal.
What is the white wire?
The white wire is the neutral. You'll bundle all the neutrals together with a "wire nut" or a twist-on plastic wire connector.
What is the black wire?
The black wire is "hot" at all times unless the entire circuit is turned off at the circuit breaker panel.
A note about wire colors: The National Electric Code requires that every neutral wire be colored white, and that ground wires be colored green. Only neutral wires may be white in color, but the code makes an exception for white wires in a cable that are not being used for a neutral. These wires should be colored black using a magic marker or some other method. Many electricians will do this, but many will not, and it can make troubleshooting in the future difficult and can be a safety hazard to anyone else working on the system. I encourage you to take the few seconds necessary to color these non-neutral wires.
The colors shown in these wiring diagrams are common color usages only. Not all electricians use the same color code (except for neutrals and grounds), so the wires could be different colors.
Identifying All the Parts of a 3-Way Light Switch
The terms "traveler" and "common" have already been explained, but there are other terms that will be used in this article that also need some explanation.
- Cable. The term "cable" refers to an combination of two or more wires, bundled together, usually in a sheath of insulating material. Each wire is insulated separately, with the possible exception of the ground wire. The ground wire may be insulated with a green color or left bare (copper), without insulation.
- Power in. The power-in cable is that cable that eventually ends in the circuit breaker panel or fuse box. It is the cable that provides the power to the lighting system.
- Neutral. This is the white wire contained in the power-in cable. It does not terminate at or connect to any switch, although it may be present in a switch box and ended with a wire nut that connects it to another neutral wire.
- Ground. The grounded wire in each switch or light fixture box. It is either colored green or left bare of insulation (copper).
- Hot wire. This is the second, black wire, contained in the power-in cable. It is "hot" at all times unless the entire circuit is turned off at the circuit breaker panel.
- Circuit breaker panel. Commonly called a "fuse box," it may contain either circuit breakers or fuses. This panel controls all the power in the building and it is where that power may be shut off.
- Two rope. "Two rope" is the designation given to a cable that has two individual wires, plus a ground wire. These wires will be colored white and black, with a green or bare (copper) ground.
- Three rope. Three rope is a cable with three wires, plus a ground. Normally the colors are white, black, and red with an additional green or bare (copper) ground.
Understanding a Wiring Diagram
Each diagram will show the two 3-way switches (but not the wall box they are contained in), the various cables and wires used in the configuration being discussed, and the light box and light fixture.
How does the electricity flow through the switch?
To understand the wiring diagram, you must know that the electrical current enters the system on the black wire in the power-in cable, passes through the switches, through the light fixture, and returns to the white wire in the power in cable. If the circuit is broken anywhere (a switch turned the wrong way, a broken wire, or a bad light bulb), the current will not flow and the bulb will not light. For discussion purposes, each 3-way switch will be considered to have the common terminal connected to the right-hand traveler terminal when in the "up" position and connected to the left-hand terminal when in the "down" position. This is not necessarily true, however, it's simply helpful for discussion purposes.
Read the descriptions carefully and compare them to the diagrams to understand the diagrams. Each diagram will have a description of how the current travels in order to light the lamp.
A is an invaluable tool here for working on electrical circuits. Both Fluke and Klein make professional-quality testers, and cheaper ones are commonly available as well. As a professional electrician for some 20 years, there is always one in my pocket, and anyone working around electricity should carry one as well. non-contact voltage tester
Turn off the power before starting to work!
Installing the Light Switch
Once the correct location of each wire is determined using the wiring diagrams below, the light switch is connected to proper wires and installed in the light switch box. Make sure the power is off before making any connections!
Older switches vs. newer ones:
Many residential light switches have a small hole in the back of the switch that wires can be pushed into, and all switches have the screws on the side. The picture of the older switch above has both the push-in holes and screws; the other is an expensive switch that has holes to insert wire but the screws must be tightened as well. Many switches have only the screws, with no holes. There is a "strip gage" on the back of the switch; it shows how much insulation is to be stripped off if the push-in method of connection is to be used. If the screws are to be used, a little more insulation needs to be removed.
How to attach the wires to the screw terminals:
- If the screws are to be used for connection, bend the end of the stripped wire into a half circle using needle-nose pliers, and wrap the wire around the screw in the clockwise direction.
- Tighten each screw firmly.
- Fold the wires neatly back into the wall box and push the switch into the box.
- Normally the ground screw goes down, toward the floor, but it can be inserted in the up position with 3-way and 4-way switches.
3 Way Wiring Diagram #1
Wiring Diagram #1, Power In the Light Box
In this example, the power-in cable enters the light box. This method of running the wire is common when several light fixtures share one common breaker, and the switches are both on the same wall. Cables need to be run into the light box, between the two switches, and from the light box to just one of the switches.
Lets follow the current as it lights the lamp in the light fixture:
- The current enters the light box on a black wire, as it always does.
- That wire is spliced to a white wire in a two-rope cable that goes to the first switch box (not the switch), where it is spliced to the white wire in a three rope cable and continues on to the second switch, at the common terminal.
- If the switch is up, it will exit the switch on the right-hand traveler terminal and continue on the red wire back to the traveler terminal on the first switch.
- If that switch is also up, it will exit that switch from the common terminal on the black wire in the two rope cable from the light switch.
- Continuing down that black wire, the electricity enters the light box where it goes to the light fixture.
- The current will pass through the light, exiting on the white, neutral wire and returning to the power-in cable.
A note about the color of the wires: In this example, the only neutral wires are the white wire in the "power-in" cable (which is always a white wire) and one of the two wires attached to the light (also always white). All other white wires should be colored.
3-Way Wiring Diagram #2
Wiring Diagram #2, Power in Light Box
In this 3-way switch wiring diagram, the power-in line enters the light box, but 3 rope cables are then installed between the light box and each switch box. This method might be used when power is available in the ceiling but switch boxes are on opposite walls—it is often easier to run the cable up into the ceiling light box instead of between switches.
If the current is followed...
- it comes into the light box on the black wire
- then flows to the common terminal on one switch using a (colored) white wire
- it exits the switch from a traveler terminal
- then returns to the light box, where it is merely spliced to another wire that goes to a traveler terminal on the second switch
- it goes through that switch, again exiting from the common terminal, and once more enters the light box, where it goes to the light itself.
- The neutral goes from the power-in cable directly to the light fixture.
3-Way Wiring Diagram #3
Wiring Diagram #3
This time the electrician has brought power into the first switch, through the second switch, and on to the light fixture. This is a reasonable method for cases with multiple switches in the same box, as other switches then have power available and can operate other lights without having to have a separate power in line run to them.
The major difference here is that the neutral from the power-in line has to be taken to the light fixture via the 3 rope. The white wire must be used here, as code requires that all neutral wires be white.
Following the current...
- it enters the first switch box on the black wire and is connected to the common terminal.
- If the switch is in the "down" position, it exits the switch on the red wire, entering the second switch at a traveler terminal.
- If that switch is also down, it exits that switch on the black, common, wire and continues to the light.
- After passing through the light fixture, the current returns to the second switch box on the white wire, is spliced to another white wire in the 3 rope used between switch boxes, and continues to the first switch box, where it is spliced to the white power in wire and back to the fuse box.
- The circuit is complete and the lamp will light.
3-Way Wiring Diagram #4
Wiring Diagram #4
This example shows the power-in cable entering the first switch box along with the cable to the light fixture. This can result in a lot of wires in this box, but can be helpful when the light is near the first switch box. A larger box may be necessary to contain all the wires.
Following the current...
- it enters the switch box on the black wire at the common terminal.
- If the switch is up, it will exit the box on the red traveler wire and continue to the traveler terminal at the second switch.
- If that switch is also up, it will exit the switch at the common terminal on the white (colored) wire and return to the first switch box where it is spliced to the black wire in the 2 rope going to the light.
- Passing through the lamp, it returns on the white (neutral) wire to the first switch box, where it is spliced to the white (neutral) wire returning to the fuse box.
- The circuit is complete and the lamp lights up.
Commonality In All Wiring Diagrams
- Common to all of these wiring diagrams is that the neutral, white wire from the lamp connects directly to the white, neutral wire from the power-in cable without ever terminating on a switch. It may or may not be spliced to another white wire in a box, but never terminates on a switch—only on the light fixture.
- The black power-in wire always goes to the common on a switch, often "changing colors" through the necessity of splicing to different cables. No matter what color, one switch will have a common terminal connected directly to the power-in black wire.
- The other common terminal on the other switch always goes directly (although perhaps again spliced) to the light fixture. It does not terminate on the other switch.
- There are two traveler wires; they always go directly from one switch to the other. Neither traveler wire ever terminates at the light fixture, the power in cable, or on anything but a traveler terminal, although it may splice to a different cable somewhere.
- Neutral wires are always white, and white wires not connected to the white power in wire should be colored some other color.
- Ground wires are always green or bare of insulation (copper). Each switch, as well as the light fixture, must have a ground wire terminated to it. The only exception is older homes that do not have ground wires in the boxes; if there is a ground wire in the box it must be terminated on the switch and light.
A final note about building codes:
Recent code changes require that each switch box have a neutral wire in it. This means not only a white wire, but a white wire that is connected to the white wire on the power in cable. This rule is intended to provide future capability for the use of a dimmer or other device that may need a neutral wire and stop homeowners from disconnecting or using the ground wire for other purposes. New work (such as adding a new three-way switch) will need to comply with this code.
Which method or diagram is the best to follow?
The only wiring diagram shown here that is legal to use is #3, although #1 could be modified by adding a 2-wire cable from the lower box to the light. Any neutrals in the switch box that are unused are either spliced together or, in the case of a single neutral, simply capped off with a wire nut and tucked back into the box.
Am I required to replace all the wiring that doesn't meet the current code?
Simply replacing a switch does not mean that the room needs to be re-wired, as the existing wiring is "grandfathered in" and is acceptable. Old work does not need to be re-done to comply with the code and is this why the unacceptable (by current code) wiring diagrams are discussed here in this article.
Other Articles and Links That Might Help You
In general, switches are not difficult to replace or install, and most homeowners are quite capable of doing it. For more help and guidance, read Installing or Replacing a Light Switch.
If you are adding a new light fixture to work with your new 3-way switches and want some help, read Installing and Wiring a Light Fixture.
Regardless of whether you are replacing a switch or installing new switches in a major remodel, probably the most useful tool to own is a non contact AC voltage detector. Make sure that whenever you do any kind of electrical work that you first test with a good voltage detector.
This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.
Questions & Answers
My three-way switch is over fifty-years-old. There is a white wire on one side of the box (on the bottom), and a red wire on the same side(top). On the other side, there is a black wire (top). The new three-way switch box has a green screw at the bottom on one side, and a black screw on the other side at the bottom, with two gold-colored screws at the top. Can I attach the wires to the new box in the same place as the old, regardless of colors?
Yes, but you didn't mention a ground wire (on the green screw) for the old switch. It's very doubtful it has one. If not, the new switch should get a ground wire to that green screw, which will mean finding a source for a ground wire and running it to that switch. Electrical code requires every switch have a ground wire now even though grounds were not used for many years.
Other than that, hook up the wires the same way. The worst case scenario is that the switch will not work properly, after that you will swap a couple of wires and try again until it DOES work correctly.
It's always fun trying to decipher what an electrician or homeowner did fifty years ago!Helpful 8
On a three-way switch, can it just be grounded in the box, or does it need to go to the box and then to the switch? Can it just go to the box? My house is wired just to the box, but I have been told it should also go to the switch.
Current electrical code requires that all switches be grounded. It is easy enough to add a short "pigtail" from the box to the switch, if the box is metal and already grounded.Helpful 7
I have a setup that looks like “3 Way Diagram #1,” based on the configuration of the two switches (I haven’t located the lightbox yet), but when I separated both switches from the wires, all of the traveler lines went hot. The white wire “power-in” cable remained hot, as well. How can this happen? Is it possible that this is actually a 4 way, and I’ve just failed to identify an additional switch?
As traveler wires go from one traveler terminal on one switch to a traveler terminal on the other switch, it is not possible to remove both ends from the switches and have the wire be hot. It is not connected to anything at all, and cannot be hot.
What kind of tester are you using to determine if a wire is hot? The non-contact testers mentioned in the article can be sensitive enough to pick up static electricity transferred from one wire to another even though they are not touching. They are intended to ensure a wire is dead, and I've never had one give a false negative (showing a dead wire), but the price is that occasionally they can show hot when a wire is not.
If the wires are hot when disconnected, then there is another source of power that you have not identified yet, and the wires are going somewhere you are unaware of. It is doubtful that it is a 4-way switch - those have four terminals on them (plus ground), and they are all travelers. No power line should ever terminate on a 4-way switch.Helpful 4
Can a dimmer switch be installed in a three-way switch set up?
Yes, but a 3-way dimmer switch must be used. Most dimmer switches will not work.Helpful 3
© 2010 Dan Harmon