5 Common Problems When Wiring a 3 Way Dimmer Switch

A white dimmer switch.
  • 2-3 hours
  • Intermediate
  • 40-60
What You'll Need
Dimmer Switch 3-Way switch Wire connectors Screwdriver Voltage Tester
What You'll Need
Dimmer Switch 3-Way switch Wire connectors Screwdriver Voltage Tester

You can put your lights on a dimmer switch in no time. With a few tools and your handy wiring diagram, you can add a custom lighting solution to any room in your house.

Some dimmer switches are set on a 3-way switch. This means that the lights can be turned on and off from the dimmer switch as well as another light switch. These types of switches are common in hallways and staircases. They are often found in large rooms as well. If you avoid the five problems below, you will wire your 3-way dimmer switch like a pro.

Common Problem 1 - Buying the Wrong Size Switch

You should calculate the maximum fixture wattage before you buy your dimmer switch. The maximum wattage should be clearly marked on the fixture. You may have to take the bulb out to read it, however. Once you have located the maximum fixture wattage for each individual lamp, you will need to add them up. That number will help you determine the perfect size of the switch you need to purchase.

For example, if you have wanted to connect the dimmer switch to four recessed lights with a maximum wattage of 75, you will multiply 75 by 4. The maximum wattage for those fixtures is 300. That means that your new dimmer switch will have to be able to handle a load of 300 watts.

Make sure that you check the fixture for the wattage and not the light bulb currently installed. This method can yield a total too high or too low.

Common Problem 2 - Miswiring of the switches

Two white dimmer switches.

When checking for miswiring, you have to identify into which of the terminal boxes is the power source going. Before doing anything else, the breaker must be turned off, so that there is absolutely no power coming from that line. The Neutral (white) wires from the power source cable and the outgoing feed (a 3-wires cable) should be connected together as in the second junction box containing the second switch where the white from the light fixture should be connected to the white from the first switch.

Next, the Hot wire (black) from the panel needs to be connected to the black wire on the dimmer switch, and the red wire from the 3-wire cable is connected to the red wire on the dimmer switch while the remaining black wire is connected to the last wire on the switch.

Finally, at the second switch, the black wire from the light fixture is connected to the common terminal while the remaining black and red wires from the first switch are connected to each of the remaining terminals on the second switch. If you want ON and OFF to work in the opposite direction, reverse the black and the red wires on this second switch.

Common Problem 3 - Failing to Ground the Switch

You will need to locate the ground wire and connect that to the switch as well as to the ground on the junction box. The ground wire is what prevents stray current from electrocuting your family and possessions. The ground wire is often white, green, or bare.

Common Problem 4 - Using Improper Bulbs

A white dimmer switch.

Unless otherwise noted on the packaging, dimmer switches should not be used with fluorescent or common energy-saving light bulbs. They are designed to work with incandescent bulbs.

Common Problem 5 - Not Checking Both Switches

Before you put up your tools and tidy the work area, you need to make sure that the lights work from both light switches. If you fail to check both switches, you may find that one of the switches doesn’t work. If that is the case, you will have to pull your tools out and remove the switch to determine the problem. If you check both switch plates right away, you will know if you have to do any troubleshooting.