How to Wire a Three-Way Dimmer Switch. Three-way switches can commonly be found at either end of a hallway, near the doors of a very large room with multiple entryways or at the top and bottom of a set of stairs. They allow you the ability to turn the lights on or off from either location. But if you have a long hallway and you want to add a little ambiance to it or you just want to cut down on the harsh glare of the incandescent bulb, you can satisfy your need by replacing one of the conventional three-way switches with a three-way dimmer switch. Here is how.
Things You'll Need
Three-way dimmer switch
The first thing you will have to realize is that you can only replace ONE of the existing three-way switches with a three-way dimmer switch. If you try and replace them both, the circuit will not work. Therefore, choose to replace the three-way switch that you will probably use the most to control the lighting.
Find the circuit breaker that is delivering the power to the lighting circuit and toggle it OFF. Flip each three-way switch to make sure the circuit is off.
Remove the cover plate from the switch and remove the two screws securing the switch to the wall box.
Gently pull the switch out of the box by pulling on the top and bottom tabs. Do not touch the sides of the switch. With the switch out of the box, use your voltage tester to ensure that the circuit is truly off.
Take a moment and look at how the switch is wired. One side of the switch should have a single red wire attached to it and the other side should have either two black wires and the ground or a black wire, a white wire with a strip of black electrical tape on it and the ground wire.
Remove the red wire and bend it out of the way. Remove the two black wires (or the black and taped white wires) and bend them out of the way. Bend the top wire upwards of the box and the bottom wire toward the bottom of the box so you will know where they get connected on the dimmer switch. Lastly, remove the ground wire and toss out the old three-way switch.
Check all of the wires to make sure that they are all in good condition. If any look corroded or weak, just cut off the existing exposed wire and use the wire strippers to remove about 3/4 inches of insulation so you have fresh wire to work with.
Connect the ground wire to the three-way dimmer switch first. Then, connect the red wire to the side of the switch with the solitary screw. Now, connect the other two wires to the other side, keeping in mind which one goes on top and which one gets connected to the bottom.
Wrap a tight layer of electrical tape around the three-way dimmer switch to protect the terminals. Gently push the wires back into the box and secure the dimmer with the two screws that came with it. Lastly, replace the cover plate with one that properly fits the dimmer molding.
Toggle the circuit breaker back on and try out your new three-way dimmer switch!
Make sure the three-way dimmer you purchase is rated for the combined wattage of all of the lights it will be operating. Make sure that the bulbs in the fixtures are capable of being dimmed, as not all are.