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How to Install a Lamp Dimmer

Would you like to be able to adjust the illumination of a table or floor lamp? This article will help you understand how to install a dimmer switch either in the socket or on the cord of a portable lamp. If you want to install a dimmer on built-in lighting, please see How to Install a Dimmer Switch.

Lamp-cord dimmer simply plugs into the wall outlet and receives the lamp cord. Photo: Lutron

Lamp-cord dimmer simply plugs into the wall outlet and receives the lamp cord. Photo: Lutron

Lamp dimmers, sold online and in hardware stores, come in a few different varieties. They are intended for controlling different types of lamps, from incandescent to compact fluorescent (CFL) to LED, so it’s important to pay attention to the specifications. These are the main types of lamp dimmers:

Screw-in lamp-base dimmer is touch controlled. Photo: Westek

Screw-in lamp-base dimmer is touch controlled. Photo: Westek

• Plug-in table or floor lamp dimmers allow you to simply plug your lamp into the device, plug the device into the wall, and dim the lamp from the device.

• In-line lamp cord dimmers, which can be attached to a lamp cord, are the least expensive type—they mount directly on the cord.

• Lamp-base dimmers screw directly into a lamp’s socket. Some are controlled just by touching them.

Installing a Lamp Cord Dimmer

You can buy a lamp cord dimmer online or at a hardware store or lighting shop. Here are directions for wiring a cord dimmer:

1After making sure your lamp is unplugged, use a utility knife to separate the two wires in your lamp’s cord.


2Determine which wire is neutral and which one is hot. This isn’t always easy to discern but, in many cases, the hot wire has smooth insulation, and the neutral wire is ribbed. Slice through the hot wire where you wish to install the dimmer.

Lamp cord dimmer costs less than $4 and is easy to mount on the cord. Photo: Leviton

Lamp cord dimmer costs less than $5 and is easy to mount on the cord. Photo: Leviton

3Use wire strippers to strip about 1 inch of insulation from both ends of the cut hot wire.

4Unscrew and remove the cover of the dimmer switch. Place the neutral wire along the inside of the switch box, as specified by the manufacturer. Put the cut ends of the hot wire under the two terminal clamps, and fasten them in place by turning the screws.

5Screw the dimmer switch’s cover back into place. Plug the lamp in, and check to make sure the new switch works.

Installing an Electronic Timer Switch

It is fairly simple to replace a standard wall light switch with a timer switch. Following are instructions for how to affix a timer that has a neutral white wire. If your timer has no such wire, follow the instructions outlined in How to Install a Dimmer Switch.

Versatile heavy-duty timer can control fluorescent or incandescent lights, motors, and more. Photo: Intermatic

Wiring a timer switch is just like wiring a regular light switch or dimmer.  Photo: Intermatic

1Make sure the electricity is shut off to the circuit. Remove the cover plate and the existing light switch.

2Divide all the wire ends so that they are not in contact with one another or with the switch box.

3Turn the power back on to the circuit and use a voltage tester to test the pairs of black and white wires. (The wires that cause the tester to glow are the wires that supply the box with power.)

4Turn the power off again. Begin splicing the wires in the box together with the leads of the timer switch, starting with the green ground wire and green ground lead (if there is a green wire and lead) and continuing on to the neutral white wire and white lead.

5Next, splice the “hot” wires, the box’s black wire to the switch’s black lead. Splice the final switch lead to the other black wire in the box.[GARD align=”right”]

6Tuck all the wires into the switch box, and screw the timer switch onto the wall.

7Finally, screw the cover plate back into place, then turn the power to the circuit back on.

How to Wire Three-Way Light Switches

These diagrams illustrate how to wire a pair of three-way light switches in three different situations.

Three-way light switches, used where you want to control a light from two locations, such as from both ends of a staircase or hallway, are built and wired a little differently than a conventional single-pole light switch. For starters, they don’t have “OFF” and “ON” printed on the toggle, and they don’t have a top and bottom.

Three-way switch wiring where power connects to first switch and then the light.

Also, rather than having two terminal screws like a conventional single-pole light switch, a three-way switch has three. On most of these switches, two of the terminals are the same color (typically silver or brass), and the third terminal, called a “common terminal,” is a different, often darker, color. Not all three-way switches have these terminals placed in the same configuration, so you have to pay attention to their colors when wiring them.

To buy three-way switches online, see Three Way Switches.

When replacing a three-way light switch, be sure to return the wires to the proper screw terminals. On three-way switches, two terminals are the same color and the third terminal—called the common terminal—is a different metal or color. Put a piece of tape on the wire that goes to the common terminal screw. The other two wires can attach to either of the identical terminals.[GARD align=”left”]

Refer to the illustrations on this page for doing the rough-in wiring for each of these situations. Note that these diagrams assume that you’re following all recommended practices for safe installation of electrical circuits and that the power to the circuit is always turned off when you are working with exposed wires.

It’s important to recognize that a light switch is designed to interrupt the “hot” wire when it’s turned off. With this in mind, the white wire from the power source always goes uninterrupted to the light fixture and the bare grounding wires are always fastened to grounding screws.three-way-light-switch-diagram-23c

With a three-way switch, three wires connect the pair of switches—two black “traveler” wires and a third “common” wire. When the circuit’s power is turned on, any of these may be “hot,” depending upon how the switches are toggled. Because “3-wire-with-ground” nonmetallic electrical cable such as Romex contains a white wire, the white wire can be painted or taped black to serve as an additional black (hot) wire when used as the connecting wire between two three-way switches.

How 3-Way Switches Are Wired

Three-way switch wiring where power goes directly to the light.

There are three basic ways three-way switches may be set up to control one or more lights. The right one for you will depend upon the placement and relationship of the switches and lights.

Please note: All switches that have a green grounding screw or wire must be grounded to the metal electrical box or to the circuit’s bare or green ground wire.

A) The wires from the power source may enter one switch box first, then travel to the light, and then terminate at the other switch (shown above right).


B) The wires from the power source may enter the light fixture box first, then travel to one switch, and then connect that switch to the other switch (see illustration at left).

Three-way switch wiring where power starts at one switch and goes to second switch before traveling to the light.





C) The wires from the power source go from switch to switch, and then go to the light (see illustration at right).

Get a Pre-Screened Local Electrical Wiring Pro

How to Install a Dimmer Switch

A dimmer switch is great for taking control over the way a room is lit. It gives you the ability to make subtle changes in light levels—to set the mood in a dining room, lower the levels in a child’s room, or even give you flexibility with outdoor lighting.

Dimmer slowly raises and dims light level to brightness set by small slider. Photo: Lutron

Dimmer slowly raises and dims light level to brightness set by small slider. Photo: Lutron

In addition to these aesthetic benefits, a dimmer also has a couple of important, practical pluses. First, a dimmer saves energy by allowing you to tailor electricity usage very precisely, eliminating waste. It also extends the life of most lightbulbs because it minimizes or eliminates the “filament shock” when you flip on a conventional light switch.[GARD align=”right”]

Replacing a conventional light switch with a dimmer switch is a relatively simple task, even if you’re only a moderately experienced do-it-yourselfer. (Note: If you intend to use fluorescent bulbs in the lighting circuit, you will need a different kind of dimmer.) To buy dimmers, see Dimmer Switches.

A dimmer switch can cause a lightbulb’s filament to vibrate, creating a buzzing sound when the light is on a less-than-full setting. You can buy a new dimmer that’s designed not to buzz and replace the switch, but before you do try replacing the bulb with a “long life” lightbulb that has a sturdier filament and is rated 130 volts instead of the far more common 120 volts.

Remove the wall plate and unscrew mounting screws.

Just remember the cardinal rule: Always shut off the power to an electrical circuit before working on it. Turn off the circuit breaker at the electric service panel, and then refer to the following step-by-step procedures:

1Use a screwdriver to remove the wall plate. Then unscrew the switch mounting screws.

Pull the switch out by it’s flanges.




2Grasp the switch by its flanges and gently pull it straight out of the mounting box. With a neon tester, double check to make sure the circuit wires are not electrically charged. It won’t light up unless there is still power in the circuit.



Unscrew the wires from the switch terminal.

3Unscrew the wires from the switch terminals. If they are poked into holes in the back of the switch, use a small screwdriver to release them. Straighten the ends of the wires, or, if possible, snip them off and strip the ends again.

Connect the switch’s ground wire.



4Use lineman’s pliers to twist the bare end of the green ground wire together with the bare copper ground wire in the box. Then use a wire nut to further connect the dimmer’s ground wire to the circuit’s bare copper or green ground wire.


Connect the light switch wires.


5Connect one of the dimmer’s black wires to each of the two black wires in the box using wire nuts.


Double-check the connections and replace the switch.


6Make sure the connections are tight, and then carefully push the wires into the box, leaving room for the dimmer. Position the dimmer, and screw it to the mounting holes in the box.


Replace the faceplate.

7Replace the faceplate. Turn the power back on at the electrical panel, and then try out the switch.

Standard Light Switch Wiring

Switches open and close electrical circuits, allowing power to flow through lights and appliances. At one time, they were pretty simple—just a toggle you flipped on and off. But things have changed.

Standard Light Switch Diagram

Switches should match the amperage and voltage ratings for the electrical circuit they serve. If your home has aluminum wiring, be sure the switches attached to that wiring are designated “CU-AL” for compatibility—otherwise, they can present a fire hazard.

Single-pole Switch Wiring Diagram

The simplest and most common light switch is actually referred to by hardware dealers and electricians as a “single-pole light switch.” With a single-pole light switch, flipping the lever up completes the circuit, turning lights or appliances on, and flipping it down breaks the circuit, turning lights or receptacles off.[GARD align=”right”]

A single-pole switch has two brass terminal screws on the side that receive the black and white wires of the circuit. (The number of terminal screws identifies the type of switch.) Modern single-pole switches also have a green grounding screw (not shown) that connects to the circuit’s ground wire.

The type of switch that will operate hallway lights from either end of the hallway is called a three-way switch; it has an extra terminal.

3-Way Light Switch Wiring Diagram

Central Lighting Control Systems

The ultimate in multi-station controls is a central lighting system. Based on commercial lighting systems, these are sophisticated, microprocessor controls. Made by several major manufacturers, they let you monitor and control many different switches and dimmers throughout the house from a central control panel. At a glance, you can tell which lights are on, and, with the touch of a single button, you can turn all of the lights on or off.

Some, like Honeywell’s LiteCom, can be configured so that you can control any light from any switch. Most are meant for new, custom-built homes—the house’s wiring generally must be installed specially for the system.[GARD align=”left”]

Another model, the LiteTouch control station, is the same size as a normal light switch cover but operates nine different circuits. Multiple-station controls can be pre-set so that, with a single touch, they provide candle-like atmosphere in the dining room; relaxed, tranquil lighting in the living room; and bright, activity lighting in the kitchen.

Grafik Eye lighting control is a wireless unit that controls six lighting zones. Photo: Lutron

Grafik Eye lighting control is a wireless unit that controls six lighting zones. Photo: Lutron

Similar controls can be programmed to handle several circuits in one room—Lutron’s Grafik Eye, for example, switches or dims up to six different lighting zones. With it, you can pre-set light levels for each zone based on activities such as “Party,” “Reading,” “Cozy,” and “Family,” and then just push one button to activate those settings. You can set up fade times, create paths of light, and operate the system with a remote control.

Some central controls, such as those by AMX, Honeywell, Plexus, and Unity are the brains for a complete home-automation system. They handle heating and air, security systems, audio and video systems, and more.

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