3 Way Switch Wiring Diagrams
–Check local regulations for restrictions and permit requirements before beginning electrical work–
–Most wiring diagrams on this site include a green dot representing the integrated grounding terminal found in most metal outlet boxes. However, some older metal boxes and most plastic boxes don't have a terminal like this.
–By code, the number of conductors allowed in a box are limited depending on its size. Conductors include wires, devices like switches and receptacles, and some other metal parts. Check here to calculate the number of conductors allowed in a box before adding new wiring, etc.
Three-way switches allow for controlling a light fixture from two separate locations, these are usually used at the top and bottom of a flight of stairs or at two different entrances to a room. On this page are several wiring diagrams that can be used to map 3 way lighting circuits depending on the location of the source with relation to the lights. Included is a diagram for a 3 way dimmer and an arrangement to control a receptacle from two locations. For more information about these circuits and troubleshooting tips check below.
Source at First Switch and Light at the End
In this diagram the electrical source is at the first switch and the light is located at the end of the circuit. Three-wire cable runs between the switches and 2-wire cable runs to the light. The black and red wires between SW1 and SW2 are connected to the traveler terminals. The hot source is connected to the common terminal on SW1, and the common terminal on SW2 connects to the hot terminal on the light.
Source at First Switch and Light Between
The source in this circuit is at the first switch and the light fixture is located between SW1 and SW2. Three-wire cable runs between each switch and the light fixture. The hot source wire is connected to the common terminal on SW1. The common terminal on SW2 is connected to the hot terminal on the light. The traveler wires are spliced at the fixture box to run between the traveler terminals on the switches.
Source at the Light and Switches After
In this diagram the source for the circuit is at the light fixture and the two switches come after. Two-wire cable runs from the light, to SW1 and 3-wire cable runs between SW1 and SW2. The hot source is spliced to the white cable-wire, which is wrapped with black tape to mark it as hot and run through to SW1 where it is spliced to the black wire running to the common terminal on SW2. The hot terminal on the light fixture is connected to the common terminal on SW1. The red wire and marked white wire travelers connect the traveler terminals between the two switches.
Source and Light Between Switches
In this arrangement the source for the circuit is at the light fixture. 3-wire cable runs from the switches on each side, to the light. The hot source is spliced to the common terminal on SW2 and the hot terminal on the light fixture connects to the common terminal on SW1. The traveler wires are spliced at the fixture box and run to the traveler terminals on both switches.
3 Way Switch Dimmer Wiring
The following 3 diagrams show the wiring for a specially made dimmer that can be used in these circuits in place of either of the the 3 way switches, or both. This arrangement allows for lowering the lights in a 3 way circuit. After the dimmer level has been set the other switch will turn the lights off and on at that level. This device can be used in place of any of the 3 way switches in these circuits, as well as to dim the lights in a 4 way circuit.
Instead of terminals, a 3 way dimmer has 4 wires coming out of the casing: one common, two travelers and one ground wire. The common wire is usually black and the travelers red. In any case, the traveler wires will usually be the same color to distinguish them from the common wire.
In this circuit the source hot is at the common on the 3 way switch and 3-wire cable runs from there to the dimmer. The traveler wires run between the 2 switches and 2-wire cable runs from the dimmer to the light. The neutral from the source is spliced at each box to run through to the neutral terminal on the light fixture. The common on the dimmer is connected to the hot terminal on the light fixture.
This diagram is the same as the one above but the dimmer comes first in the circuit. This arrangement is provided for easy reference when dealing with a circuit wired like this.
Here the source is in the middle of the circuit. The dimmer switch is in this box where the hot is connect to the common wire. The common on SW1 is run to the light fixture hot terminal using the white cable wire to the dimmer box where it is spliced with the black cable wire going to the light. The white wire is wrapped with black tape to mark it as hot. The traveler wires are connected in the same way as the above diagrams. The neutral runs directly from the dimmer box to the light fixture.
In this arrangement two 3-way dimmers are used to allow for lowering the lights from both locations. Here the common on the first dimmer connects to the hot source and the common on the second connects to the hot on the light. As with all these types of circuits the traveler wires run between the switches and connect the traveler terminals.
Controlling a Wall Outlet from Two Locations
This diagram shows the wiring to control a receptacle outlet with two 3 way switches. The source is at SW1 and 3-wire cable runs between all the devices. The hot wire from the source connects to the common terminal on SW1. The common on SW2 is connected to the hot terminal on the receptacle. The traveler wires are spliced in the receptacle box to run to the traveler terminals on each switch. The white cable wire is used as a traveler to SW2 and marked hot with black tape.
Add a Receptacle to a 3 Way Circuit
Here a receptacle is added to the circuit before the first switch. It is not controlled with the switches but is instead always hot. The source hot, neutral and ground are spliced to a 2-wire cable that runs to the new outlet. The 3 way switches and light are then wired in the usual way with the common on SW2 spliced to the source hot and the light hot wired to the common on SW1.
About 3 Way Switches
Three-way switches have 3 terminals to carry circuit electricity and one terminal for a ground wire. Of the three circuit terminals, one is called the common and the other two are known as travelers. The common terminal may be labeled and is usually a different color than the traveler terminals. Depending on the manufacturer, the travelers may be on opposite sides of the device or the two terminals may be on the same side. In any case, the common terminal will be distinguished from the travelers in some way.
The common terminals will always be connected to a hot wire, either from the source or on the light fixture. These connections can be reversed if it's more convenient, as long as one of the 3 way common terminals connects to the hot source and the other one connects to the hot on the load, these circuits will work properly. The traveler terminals will always be connected from switch to switch. Travelers never connect to a device load or to a source wire. It doesn't matter which traveler terminal is used for which traveler wire, reversing them should make no difference.
Troubleshooting 3 Way Circuits
If your switches stop working they may be worn out or the screws may have come loose. If you've wired a new switch correctly and the circuit still doesn't work, the switch may be defective. Check that all connections are tight. Check the switch, remove it from the circuit and test for failure with a continuity tester or multimeter set on the Ohms setting.
If the switch is good and things still don't work, check the wiring to be sure the hot source is connected to a common terminal and the light fixture hot is connected to a common terminal. Likewise, be sure the traveler terminals are connected between switches only and not to any hot wires or the load. Also be sure the neutral from the source is connected to the neutral terminal at the light. A neutral wire will not be connected to the switches in these circuits, although some smart switches may make use of a neutral wire to operate the device.