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How to Install a Dimmer Switch

Installing a dimmer switch is one of the easiest DIY electrical projects you can do. Read these steps on how to install one in your home.

Controlling the level of lighting in a room is a great way to set a mood. While you may want brighter light for reading, you might want less light for watching TV, and perhaps even a third level of light for a romantic evening at home. Dimmer switches can accommodate all of these circumstances.

Replacing a regular switch with a dimmer switch is one of the easiest DIY electrical projects. In most cases, no permit or inspection is required, but it is important to be careful whenever working around electricity.

Safety Check: Is the Power Off?

Any time you’re working with electricity, be sure to turn the power off at the panel and follow these steps:

  • Check to be sure the circuit is dead by flipping the existing switch on and off before removing the switch plate.
  • Once the plate is off, it’s a good idea to check the wires in the electrical box with a voltage tester, just to be sure.
  • If there’s more than one switch or a receptacle in the same box, check the second device’s wires with the voltage tester as well. Sometimes more than one circuit feeds into the same box.

How to Wire and Install a Dimmer Switch

One difference between dimmer switches and regular switches is that with the latter, the house wires attach directly to the switch. Most dimmers, on the other hand, come with integral wire leads that connect to the house wires using wire nuts.

Here is how to wire the new switch:

  1. Remove the screws holding the old switch in place and pull the device out of the box.
  2. Cut the existing wires as close to the switch as possible. There are good reasons for cutting the wires rather than disconnecting them. If the wires attach to the switch with screws, they’ve already been bent and fatigued. Reattaching them might break the wires inside the wire nut. If that’s not noticed during installation, you could be setting the connection up for an arc fault, which can start a fire. And if it’s the kind of switch where the wires stab straight into the back, they’re hard to remove in any event.
  3. Strip about 3/4 inch of insulation back from the freshly cut wire ends and attach them to the leads on the dimmer.
  4. Match wire-color to wire-color, joining the bare ground wire with the green wire from the switch.
  5. Hold each pair together so that the ends of the insulation align and twist the wires together in a clockwise direction with linesman’s pliers.
  6. Twist until the insulated sections of the wire have wrapped around each other. That helps to prevent any future tension on the connection.
  7. Finish the connection by twisting on a wire nut, again in a clockwise direction.
  8. Give each wire nut a tug to be sure the connection is sound, then feed the wire back into the electrical box, followed by the new dimmer switch.
  9. Screw the dimmer to the box and install the cover plate. Most dimmers require a Decora-style plate, which has a rectangular opening for the switch, so you may need to purchase one of them as well.

Make Sure Switches and Light Bulbs are Compatible

Not too long ago, the only dimmer switches you could buy were rheostats that reduced the amount of electricity going to the light by turning some of it into heat at the switch.

Without delving too far into physics, the advent of semi-conductors has changed how modern dimmer switches control electricity. Dimmers no longer generate much heat and work by modifying the wave-form of how the power flows.

The important thing to know when buying a dimmer switch now is what type of light it will control. Is it a compact fluorescent? LED? Halogen? Particularly with fluorescents and LEDs, it’s important to have dimmable bulbs as well as to have a dimmer switch that’s rated for that type of light.

Read the manufacturer’s labeling carefully when buying light bulbs to make sure they will work with a dimmer switch. You’ll also need to check the capacity of the dimmer. If, for example, there are ten one-hundred-watt bulbs on that lighting circuit, the dimmer must be rated for at least 1000 watts.

What Are Three-Way Dimmers?

A three-way circuit controls a light from two locations and requires special switches. Four-way circuits are similar but control the light from three or more locations. Rather than using cable with two insulated wires (one black and one white) plus a bare ground, these circuits use cable with three insulated wires (black, white, and red) plus a bare ground.

The main difference is that you have to pay close attention to the existing switch. One terminal on that switch will be black. The wire that leads to that black terminal must connect to the black wire on the new dimmer switch.

Otherwise, the job is similar. Once you’ve put everything back together, flip the breaker back on and enjoy the new atmosphere you’ve created.