How to Install a Single-Pole Dimmer Light Switch

Installing a light switch
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Overview
  • Working Time: 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 through use of a dial, slider, or some other control that operates internal circuitry. While older-style dimmers used a mechanical resister dimmed lights by dissipating excess current through heat, modern dimmers are electronic devices that actually interrupt the current many times each second to limit current flow to the lights The switch can turn the light on, shut it off, or set the illumination for any 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 when you want to control lighting from two switch locations.

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

Dimmer switches are typically connected by means of wire leads that are joined to circuit wires using wire nuts or another type of approved wire connector. The switches have somewhat larger bodies than standard switches, and you may run into difficulty if the switch box is too small to comfortably hold the dimmer switch. In some situations, you may need to install a larger electrical box to safely hold the new dimmer. Some dimmers produce a small amount of heat during operation, so it is important that the box not be so crowded that heat is trapped.

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.

Traditional single-pole dimmer switches, like standard switches, generally have just two hot wires and a ground wire, with no neutral wire connection. Installation is a simple matter of connecting the hot wire leads to the hot circuit wires—one of which is entering the box from the power source, the other leading to the light fixture. The neutral circuit wires, if present, are simply joined together in the box. The grounding lead on the switch is either joined to the circuit ground wires or is bonded to a metal box.

However, some newer dimmer switches designed for use with CFL or LED lights contain a microprocessor that requires a neutral wire connection, and they may also require that you distinguish between the line hot wire (entering the box from the power source) and the load hot wire (leading onward to the light fixture). Always read the directions carefully for the particulars of your switch.

Some dimmer switches can be used in either single-pole or three-way configurations. With this type there is an extra wire lead—usually red with white stripes—that comes into play only when your are installing the switch as part of a three-way installation. If you are installing this type of switch as a single-pole switch, you simply cap off this extra wire.

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.

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 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.

    Removing light switch plate
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  3. Remove the Switch Mounting Screws

    Backout the mounting screws until the switch can be pulled out of the electrical box. Gripping the switch by the mounting straps, carefully extract it out 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.

    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. If your switch is attached via push-in fittings on the back of the switch, you can remove them by pushing a small nail into the release slot located next to each push-in screw terminal.

    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 wire and strip a 3/4-inch fresh section.

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

    Attaching the dimmer switch leads to the circuit wires extending from the box is fairly straight-forward 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 is already attached to the metal box, the switch grounding lead may also be attached to the box, since the metal provides a bonding pathway to the circuit ground.

    The circuit wires and switch leads are typically joined together with a wire connecter. 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 connector.

    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.

    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, just cap this wire off with a wire connector. As wire nuts tend to come off of single wires, twist a short length of electrical tape around the wire nut and 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 size of the dimmer switch's back. 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 switch body.

    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 outer edge of the box, then attach the switch cover plate.

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

    Caution

    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 in order 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.