Three-way circuits are commonly used in modern homes because they provide the convenience of controlling a light or outlet from two switches in different locations. They are slightly more complex to wire than ordinary switches, and they require different materials and components.
Three-way circuits work by providing two wires between the switches, with the switches selecting between either of the two wires. When both switches connect to the same wire, the circuit is completed and the light turns on. Moving either switch to connect to the other wire turns off the light.
Instructions
Preparation and Wire Pulling
1. Turn off electricity at the circuit breaker to any circuits that are being worked on.
2. Mount the two electrical work boxes at the location where you want the switches. Switch location is governed by your local electrical code, but in general you can match the height and setback of existing switches. Electrical boxes are mounted with either screws or nails to wall studs, although "remodel" boxes are available that can mount on a wall between studs.
3. Run a two-conductor wire from a power source into the first box. Note that a two-conductor wire will have three conductors: a black, white, and bare copper wire. The wire should be an appropriate gauge and type for your application based on the manufacturers specifications.
Power may be supplied from another outlet, a nonswitched power wire at a light fixture, or from the electrical panel. Consult a licensed electrician before performing any work at the electrical panel as lethal voltages are always present.
If you connect your power wire to an existing circuit, be sure you are not exceeding the power handling capacity of either the wire or appropriate circuit breaker. Consult a qualified electrician if in doubt.
An electrician's fishtape, a long strip of spring steel, may be helpful in running this wire through existing walls. Also, for long lengths of wire, lubricating the wire before it is pulled into the wall will make the job easier.
Check your local electrical codes, but in general, wire must be secured every four feet by a staple or fastener, and not secured within one foot of an electrical box.
4. Run a two-conductor wire from the light being controlled to the second electrical box.
5. Run a three-conductor cable between the two new electrical boxes.
Connections at the Light Fixture
6. Identify the ground wire coming from the light fixture. This will usually be green in color, or bare copper wire. If the ground wire from the light fixture is insulated, strip approximately 1 inch of insulation from the wire.
7. Identify any other ground wires, either from additional circuits or attached to the electrical box. There may not be any additional wires present.
8. Use your utility knife and make a cut lengthwise along 5 inches of the outer covering of the two-conductor cable. Pull this cable apart and trim the outer insulation. Remove any inner cardboard insulation in the wire.
9. Strip about 1 inch of insulation from the black and white wires present inside the cable. Also strip an inch of the insulation from any other wires coming from the light fixture.
10. Grasp each of the ground wires and hold them together. Insert each of the ground wires into a wire connector and tighten (counterclockwise) until hand tight. Verify that each of the wires is firmly connected.
11. Using a wire connector, connect the black wire from the light fixture to the black wire of the two-conductor cable. Repeat with the white wires.
If the light fixture does not have color coded wires, the wires may be connected in either order.
12. Push all wires neatly into the electrical box, and mount the light fixture to the electrical box per the manufacturer's instructions.
Making Connections at the First Electrical Box
13. Identify the COMMON terminal on one of the three-way switches. There are three terminals on a three-way switch, and one will be marked COM, or may be brass or black in color. The enclosed instructions with the switch should indicate the COMMON terminal.
14. Strip the insulation from the power source wire and the three-conductor wire as described in the previous section.
15. Connect the black wire from the power source wire to the COMMON screw on the three-way switch.
16. Connect the red wire from the three-conductor wire to one of the remaining terminals on the three-way switch.
17.Connect the red wire from the three-conductor wire to the final terminal on the three-way switch.
18. Connect a 6-inch piece of bare copper wire to the ground connector on the switch. Using a wire connector, connect this ground wire with the ground (uninsulated) wires from both the power source wire and the three-conductor wire.
19. Connect the white wire from the power supply wire and the white wire from the three-conductor wire together with a wire connector.
20. Using the supplied screws, mount the switch into the electrical work box and install the switch plate cover.
Making Connections at the Second Electrical Box
21. Identify the COMMON terminal on the second of the three-way switches.
22. Strip the insulation from the two-conductor wire from the light and the three-conductor wire as described in the previous step.
23. Connect the black wire from the two-conductor wire from the light to the COMMON terminal on the second three-way switch.
24. Connect the red wire from the power source wire to the common screw on the three-way switch.
25. Connect a 6-inch piece of bare copper wire to the ground connector on the switch. Using a wire connector, connect this ground wire with the ground (uninsulated) wire from both the two-conductor wire from the light and the three-conductor wire.
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Connect the white wire from the two-conductor wire from the light and the three-conductor wire together with a wire connector.
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Using the supplied screws, mount the switch into the electrical work box and install the switch plate cover.
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