Weekend How-To: Install a Light Dimmer

You have guests over for dinner and suddenly—wham!—someone turns on the overhead light. Before you can say, “Please, no!” your dining room goes from a moody candlelit bistro to an ambiance that’s reminiscent of your middle-school cafeteria. All because your guests couldn’t see their food with the 15 candles you painstakingly placed throughout the room. And now you’re stuck dining in more than enough light to see every one of Uncle Phil’s nose hairs.

Maybe it’s time for a light dimmer. It’s super easy to install a dimmer and you’ll be able to add just a little light or a lot, for whatever mood you want to create. Plus, a dimmer can save you money and energy. So you can say “yes” to a lot more dinner parties.

Just a little heads up before you go any further: This article is for a single-pole light dimmer. To learn about the different kinds of dimmers, check out this page.

General Do’s and Don’ts for Installing Dimmers

  • DO NOT use ordinary dimmer switches with most fluorescent lights, unless otherwise noted. Use only CFL (Compact Fluorescent Lamp) bulbs that are labeled “dimmable”.
  • DO NOT use an ordinary dimmer switch with a ceiling fan; it can burn out the motor.
  • DO install a bigger wall box if there isn’t enough room in the existing wall box to easily accommodate the new dimmer.

What You’ll Need:

  • Phillips head screwdriver
  • Slotted screwdriver
  • Long nose pliers
  • Wire stripper
  • Wire cutter
  • Voltage tester
  • Dimmer
  • Dimmer wall plate (if needed)
  • Wire connector nuts
  • Electrical tape
light dimmer

Step 1: Select a Dimmer Switch

  • Determine the kind of switch you have, as this will determine the type of dimmer you need. Single-pole dimmers control the light with a single switch, while three-way dimmers control a light with two switches. (Note: This article is for a single-pole dimmer switch. Find information on other types here.)
  • Determine the type of light that will be connected to the dimmer. For CFL bulbs, make sure the dimmer switch can be used with CFLs.
  • Figure out how many lights will be connected to the dimmer and add up the total wattage. For example, if you have two 75-watt lights, your total is 150. In this case, you’ll need a dimmer that’s rated for at least 150 watts.

Step 2: Review the Manufacturer’s Instructions

  • After you purchase your dimmer, review the manufacturer’s instructions and note any steps or instructions specific to that model or manufacturer.

Step 3: Turn Off the Power at the Circuit Breaker

  • Turn off the power for the switch at your circuit breaker box or fuse box.
  • If the breaker box switches are labeled, turn off the correct switch and test the light switch to make sure the electricity is indeed turned off.
  • If the breaker box switches are unlabeled or labeled incorrectly, you’ll have to test every one of them until you locate the right one. This is when having an extra person comes in handy—one person tests the switches at the breaker box while the other one yells “yes” or “no” to signal when the correct circuit is switched.

Step 4: Remove the Old Wall Plate and Switch

  • Remove your existing wall plate by unscrewing the screws.
  • Next, remove the screws mounting the switch to the wall box and pull the switch away from the wall.

Step 5: Test the Circuit

  • Test the circuit with a voltage tester before you touch any of the wires. (Electrocution is a very real thing, people!)
  • If the tester detects voltage, you may have to turn off another circuit breaker or remove a fuse.
  • Make sure the voltage tester detects no voltage before continuing.

Step 6: Mark and Disconnect the Wiring

  • Use masking tape to mark the wires that are connected to the switch, or take a picture with your phone so you’ll know how to connect the wires to your new dimmer.
  • Disconnect the wires by loosening the screws and unhooking the wires.

Step 7: Strip the Wires

  • Before stripping the wires, double check the manufacturer’s instructions to make sure you don’t strip off too much insulation.
  • Using a wire stripper, remove ¾ inch of insulation from the end of the house wires if needed.

Step 8: Connect the New Dimmer Switch

  • Before you connect anything, make sure you have the dimmer positioned right side up.
  • Connect the ground wire from your dimmer to the green or bare copper wire in the wall box. Twist the ends together clockwise and cap them using a wire connector nut.
  • Connect each dimmer wire to a house wire by gripping the wire ends with a pair of pliers and twisting them together. (The wires from the dimmer will typically be black. The two house wires may be black, red, or white with black marking.)
  • Tighten a wire nut over each pair of wire ends. If a bare wire is exposed, unscrew the wire connector, remove the wires, trim the ends and re-cap the wires.
  • Carefully tuck the wires back into the electrical box and attach the dimmer to the electrical box using the mounting screws.

Step 9: Replace the Wall Plate

  • If you are installing a dimmer with a removable knob, remove the knob by gently pulling outward before attaching the wall plate.
  • Mount the wall plate to the switch and secure it with the screws.
  • Reattach the dimmer knob if applicable.
  • Turn the power back on from the breaker box and test the switch. If it doesn’t work, turn the power off and on again, and test once more. If it still doesn’t work, double-check your connections and consult the manufacturer’s instructions for troubleshooting details.