How to Test Continuity Between 3 Way Switchs
3 Way Switch Wiring Diagrams
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How to read these diagrams.
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. For 4 way switch wiring diagrams see these, and to wire 3-way and 4-way circuits with multiple lights see these. On this page are several wiring diagrams that can be used to map 3 way lighting circuits depending on the location of the source in relation to the switches and lights. Also included, are diagrams for 3 way dimmers, a 3 way ceiling fan switch, and an arrangement for a switched outlet from two locations. For more information about these circuits and troubleshooting tips check below.
Wiring Diagram 3 Way Switch with 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.
Three Way Switch Wiring with Light Middle
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, they are not connected to the light.
3 Way Switch Wiring with Light First
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 wire is spliced at the light box to the white cable wire running to the first switch box. There it is spliced to the black wire running to the second switch box, which is then connected to the common terminal on SW2. When a white wire is used for hot like this, it's marked with black tape or paint at the ends to identify it as hot.
Back at the light fixture, the hot terminal on the light is connected to the black wire running to the common terminal on SW1. At SW1, the red and white wires running to SW2 are used as travelers connecting the traveler terminals between the two switches. Again, the white wire is marked with black on the ends to identify it as hot.
Three-Way Switch Wiring Source in Middle
In this arrangement, the source for the circuit is at the light fixture which is located in the middle of the circuit. 3-wire cable runs to the switches on each side of the light. At the light, the hot source wire is spliced to the black wire running to the common terminal on SW2. The hot terminal on the light fixture is connected to the black wire running to the common terminal on SW1. The red and white cable wires are spliced in the fixture box and run to the traveler terminals on both switches. They don't connect to the light fixture. The white wire is marked black on both ends to identify it as hot.
3 Way Dimmer Switch Wiring Diagrams
The following 4 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 lighting level has been set on one dimmer, 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 switch circuit as illustrated at this link.
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 are red. In any case, the traveler wires will be the same color to distinguish them from the common wire.
In this circuit, the source hot is connected to the common terminal on the 3 way switch in the first box. From there, 3-wire cable runs to the dimmer in the second box and 2-wire cable runs from the dimmer to the light at the end of the circuit.
The source neutral is spliced through to the light fixture using the white cable wires at each box. The black and red wires running between the switches connect the travelers. At the dimmer, the black wire is connected to the common wire and at the other end, to the hot terminal on the light.
This diagram is the same as the previous one but the dimmer comes first in the circuit. This arrangement is provided for easy reference when dealing with a circuit wired in this arrangement.
In this diagram, the source is in the middle of the circuit along with the dimmer switch. From the dimmer, 3-wire cable runs to the other switch and 2-wire cable runs to the light fixture. The source hot wire is spliced to the common on the dimmer and the neutral is splice through to the light fixture.
At the 3 way switch, the white cable wire is marked black and connected to the common terminal. At the other end, the white wire is marked black again and spliced to the black wire running the hot terminal on the light. The black and red wires running between the switches connect the travelers together.
In this arrangement, two 3-way dimmers are used to allow for lowering the lights from both locations. Three-cable wire runs between the switches and 2-wire cable runs from the second dimmer to the light.
The common on the first dimmer connects to the hot source wire and the common on the second connects to the wire running to the hot terminal on the light. The source neutral is run through to the light fixture with a splice in each switch box. The black and red wires running between the switches are used to connect the travelers together.
Ceiling Fan 3 Way Switch Wiring
Here, a ceiling fan with a light kit is controlled with two 3-way switches. This is the same arrangement as the second diagram on this page with a fan in place of the light fixture. In this wiring, the source is at SW1 and 3-wire cable runs between each switch and the ceiling fan.
The hot from the source is connected to the common on SW1 and the neutral is spliced through to the ceiling box using the white cable wire. The black and red cable wires are connected to the traveler terminals, and at the fan, they are spliced with the black and white wires running to SW2. The white wire is marked with black tape on both ends to identify it as hot. At the ceiling box, the wires for the fan and light are both spliced to the black wire running to SW2. With this arrangement, the switches control power to the ceiling box and a pull-chain is used to control fan speed. For more ceiling fan wiring diagrams, check this link.
3 Way Switched Outlet Wiring Diagram
This diagram shows the wiring arrangement for a 3 way switched outlet. With this wiring the receptacle can be controlled from two locations.
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 and the neutral wire is spliced through to the neutral on the receptacle using the white cable wire. The black and red cable wires connect to the traveler terminals on SW1 and at the outlet box, they are spliced to the red and white wires running to the traveler terminals on SW2. The white wire is marked with black tape on both ends to identify it as hot. The hot terminal on the receptacle is connected to the black wire running to SW2 where it is connected to the common terminal. For more switched outlet wiring diagrams, see this link.
Diagram to Add an Outlet to a 3 Way Circuit
Here a receptacle is added to the 3 way 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 common on SW1 connected to the hot terminal on the light fixture. For more diagrams to add a receptacle to an existing circuit, see this link.
How 3 Way Switches Work
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 Switch Circuits
The most likely cause of circuit failure is an error in the wiring arrangement. Verify the circuit is wired correctly. Check to be sure the hot source is connected to one common terminal and the light fixture hot is connected to the other 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 load and nowhere else. A neutral wire will not be connected to a standard 3 way switch, although some smart switches and timers may make use of the neutral wire to operate the device. If you believe you have things wired correctly and the lights still don't work, you can test the switches using the following procedure.
If you have existing switches that stop working, they may be worn out or the terminal screws may have loosened over time. With the power off and the device removed from the outlet box, check that all connections are still tight using a screwdriver. If the connections are made with clamps instead of screws, tug firmly on the wires to be sure they are all still tight.
If you have an old or new switch you believe was wired correctly and the circuit still doesn't work, the switch may be defective. In these cases, you can test the internal functionality with a simple procedure. Turn off the power and remove the switch from the circuit by disconnecting the wires. Use a continuity tester or multimeter on the Ohms setting to determine if it's conducting electricity properly.
To test a 3 way switch, connect one meter probe to the common terminal and the other to one of the travelers. Flip the switch toggle one way and then the other. If the meter shows continuity with the toggle in one direction and not the other, move the probe from that traveler terminal to the other one and test again. If you find the second traveler shows continuity with the toggle in one direction and not the other, the switch is probably functioning properly. If, however, you don't find any continuity or constant continuity no matter where the probe is or how you flip the toggle, the switch is likely defective and should be replaced. One note about this test, if you are dealing with a smart electronic switch or timer, this procedure will not work to test switch function.
Source: https://www.do-it-yourself-help.com/3-way-switch-wiring-diagrams.html
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