How to Install a Single-Pole Dimmer Light Switch

Installing a light switch
michellegibson / Getty Images
Project Overview
  • Working Time: 15 - 30 mins
  • Total Time: 30 mins
  • Skill Level: Intermediate
  • Estimated Cost: $10 to $30

A dimmer switch is a light switch that regulates the flow of electricity to a light fixture through the use of a dial, slider, or some other control that operates internal circuitry. The switch can turn the light on, shut it off, or set the illumination for a range of brightness in between.

Installing a dimmer switch helps you save energy and creates a relaxing mood in any room. For most do-it-yourselfers, it is a fairly simple task to install a single-pole dimmer switch, which controls a light fixture from a single wall switch. There are also three-way dimmers, designed for when you want to control lighting from two switch locations, but they usually work for single-pole installations as well. Most new dimmers are also operable with all types of bulbs (incandescent, halogen, or dimmable CFL and LED).

Dimmer Switches and LED Light Bulbs

Traditional dimmer switches were designed for standard incandescent light bulbs, and when new LED lightbulbs and light fixtures are installed, these old dimmers sometimes do not provide the same degree of illumination control. Sometimes, you will find that the range of dimming is reduced somewhat, or that the LED bulbs do not shut off at the lowest dim settings. Sometimes LED bulbs will flicker slightly when paired with an older-style dimmer switch.

To avoid problems, make sure to buy a dimmer that is labeled for use with LED lightbulbs and light fixtures. Most of these dimmers will also work fine with standard incandescent bulbs. Also, make sure that the LED bulbs are suitable for use with dimmer switches. Not all LED bulbs are dimmable, so check the labeling to make sure they are appropriate.

Installing a Single-Pole Dimmer Switch

Installation of a dimmer switch can vary slightly depending on the manufacturer, so always read the instructions and follow their recommendations. Most dimmers, however, will follow a similar installation process.

Safety Considerations

Replacing a standard light switch with a dimmer is a relatively straightforward DIY project, but as with any electrical repair, there is the potential for dangerous, or even lethal, shock. This is a project best suited for a DIYer with some understanding of electrical circuits and experience with similar repairs. As electrical repair projects go, this is a relatively easy one. But if you are not confident in your abilities, it's best to call in an electrician.

Before working on any electrical wiring, always shut off the power and test for current using a voltage tester.

Warning

It is hazardous to cram a dimmer switch into a box that is too small or too full of wires, as it needs some space to dissipate a small amount of heat generated during use. If you have trouble getting the dimmer switch to fit, it's a sign the box is too small. The switch manufacturer may offer guidelines for the size of the box and the acceptable number of wire connections. If the box is too small, it's best to have an electrician install a larger electrical box.

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What You'll Need

Equipment / Tools

  • Non-contact voltage tester
  • Wire stripper
  • Wire cutters
  • Eye protection
  • Screwdrivers (Phillips and flat-head)
  • Needle-nose pliers

Materials

  • Single-pole dimmer switch
  • Wire connectors (wire nuts)
  • Electrical tape (if needed)

Instructions

  1. Turn off the Circuit Breaker

    Find the circuit breaker for the circuit controlling the switch and light fixture and flip it off. Circuits are often labeled by builders, electricians, or previous homeowners. But don't assume the labeling is correct; always check for power after turning off the breaker.

    Although the danger is small, explosions or sparking is a possibility whenever you are switching off circuit breakers. Therefore, professional electricians generally wear eye protection whenever turning circuit breakers on or off.

    Turn off circuit breaker
    Lee Wallender
  2. Remove the Switch Cover Plate

    With a flat-head screwdriver, carefully remove the two short machine screws holding the outer switch plate to the existing switch. 

    You will probably not be reusing this plate for the dimmer switch. In most cases, you will need to purchase a specialty plate, or one may be included with the dimmer light switch kit. Still, you may be able to reuse the plate—keep it until you've confirmed whether or not it can be reused.

    Removing light switch plate
    andrewginns / Getty Images
  3. Remove the Switch Mounting Screws

    Back out the mounting screws until the switch can be pulled out of the electrical box. Gripping the switch by the mounting straps, carefully extract it from the box. Take care not to touch the screw terminals on the side of the switch or any wires.

    Remove screws holding old switch
    Lee Wallender
  4. Test for Power

    Use a non-contact circuit tester to check each wire in the box for current. Touch the tip of the tester to each screw terminal on the switch. If it lights up, it means that current is flowing; you'll need to return to the circuit breaker panel and look for the correct breaker to shut off. If current is present, the tester will light up whenever it is in proximity to a live wire.

    If your new dimmer is located in a multi-gang box with other devices, such as an outlet or other switches, current may still be present in the box even if the circuit associated with your switch is turned off. Shut off all necessary breakers to make sure there is no current present.

    If you can't determine the right breakers to throw, then you'll need to turn off the main switch, which will cut power to the entire home.

    Tip

    Always test the operation of a circuit tester on wires you know are active. For a non-contact tester, you can insert the tip into the slots on any outlet with an active circuit to verify the tool is operating correctly.

    Confirm that power is off to old switch
    Lee Wallender
  5. Disconnect the Circuit Wires

    Detach the circuit wires by loosening the screw terminals on the side of the switch and pulling the wires free. If a ground wire is also attached, disconnect it from the green ground screw. Alternatively, your old switch might be connected with wire nuts. If that's the case, simply unscrew them and untwist the wires.

    If your switch is attached via push-in fittings on the back, you can remove them by pushing a small nail into the release slot next to each push-in screw terminal, or simply clip them off with your wire cutters and re-strip them to the proper length.

    The new dimmer switch will be connected to the circuit wires using wire nuts or another form of wire connector, so the circuit wires may need to be straightened. Straighten out any loops in the copper wires, using needle-nose pliers. If the wires are flattened, nicked, or damaged, clip off this portion of the wire and strip a 3/4-inch fresh section.

    Many new dimmers no longer have terminal wires and use screw terminals that might be similar to the ones on the switch you removed instead. If your dimmer doesn't have terminal wires, place a hook at the end of the stripped wire, wrap around the screw, and then tighten the screw.

    Remove wires from old switch plate
    Lee Wallender
  6. Connect the Dimmer Switch

    Attaching the dimmer switch to the circuit wires extending from the box is fairly straightforward since it usually involves just two hot circuit wires attaching to two hot wire leads on the switch.

    • A black wire lead on the dimmer attaches to one of the two black circuit wires in the box
    • A second black (sometimes red) wire on the dimmer attaches to the other black circuit wire in the box.
    • The green ground lead on the switch attaches to the circuit grounding wire, which is usually a bare copper or green insulated wire. If the circuit ground wire was attached to the metal box in the old setup, the grounding lead from the new switch may also be attached to the box, since the metal provides a bonding pathway to the circuit ground.

    The circuit wires and dimmer leads are typically joined together with a wire nut. No bare copper should be exposed beyond the connector. If so, remove the wire, snip a small portion of the wire, then reattach the wire nut.

    Tip

    With some advanced electronic dimmers, the wiring connections may be somewhat more complicated. For example, they may require that you also establish a neutral wire connection to the switch. They may also require that the hot line circuit wire (the one entering the box from the power source) be attached to a specific wire lead. If you have this type of switch, make sure to carefully follow the manufacturer's directions or seek professional installation.

    Attach wires to dimmer switch
    Lee Wallender
  7. Cap Off the Red/White Striped Wire

    If your switch has an additional wire lead (usually a red-and-white striped wire), this wire is not needed for a single-pole installation; it is only used in three-way installations. For a single-pole application, cap this wire off with a wire nut. As wire nuts tend to come off of single wires, twist a short length of electrical tape around the wire nut and the wire to keep them together.

    Cap off the red/white-striped wire
    Lee Wallender
  8. Complete the Installation

    Putting the dimmer switch back into the electrical box may be difficult due to the mass of wires inside the box and the dimmer switch's size. Carefully fold the wires and gently tuck them into the box. They will need to be pushed as far back as possible to make room for the dimmer body.

    Go to the service panel and flip the circuit breaker back on. Return to the dimmer switch and test its operation.

    Screw the dimmer switch onto the electrical box by threading the mounting screws into the threaded openings on the box. As the screws tighten, the switch will nudge the wires deeper into the box. Make sure that the dimmer switch is completely flush with the box's outer edge, then attach the switch cover plate.

    Screwing the plate back on the switch

    The Spruce / Kevin Norris