Tools & Materials 
Screwdriver
Circuit tester
Needlenose pliers
Wire connectors
Masking tape
A dimmer switch makes it possible to vary the brightness of a light fixture. Dimmers are often installed in dining rooms, recreation areas, or bedrooms.
Any standard single-pole switch can be replaced with a dimmer, as long as the switch box is of adequate size. Dimmer switches have larger bodies than standard switches. They also generate a small amount of heat that must dissipate. For these reasons, dimmers should not be installed in undersized electrical boxes or in boxes that are crowded with circuit wires. Always follow the manufacturer’s specifications for installation.
In lighting configurations that use three-way switches (opposite page), replace the standard switches with special three-way dimmers. If replacing both the switches with dimmers, buy a packaged pair of three-way dimmers designed to work together.
Dimmer switches are available in several styles (photo, right). All types have wire leads instead of screw terminals, and they are connected to circuit wires using wire connectors. Some types have a green grounding lead that should be connected to the grounded metal box or to the bare copper grounding wires.
Tools & Materials
Screwdriver
Circuit tester
Needlenose pliers
Wire connectors
Masking tape
Toggle-type dimmer resembles standard switches. Toggle dimmers are available in both single-pole and three-way designs.
Dial-type dimmer is the most common style. Rotating the dial changes the light intensity.
Slide-action dimmer has an illuminated face that makes the switch easy to locate in the dark.
Automatic dimmer has an electronic sensor that adjusts the light fixture to compensate for the changing levels of natural light. An automatic dimmer also can be operated manually.
HOW TO INSTALL A DIMMER SWITCH
Turn off power to switch at the panel, then remove the cover plate and mounting screws. Holding the mounting straps carefully, pull switch from the box. Be careful not to touch bare wires or screw terminals until they have been tested for power. In new switch wiring, the white wire should not supply current to the switched device and a separate neutral wire should be available in the switch box.
Disconnect the circuit wires and remove the switch. Straighten the circuit wires, and clip the ends, leaving about 1/2" of the bare wire end exposed.
Connect the wire leads on the dimmer switch to the circuit wires using wire connectors. The switch leads are interchangeable and can be attached to either of the two circuit wires.
A three-way dimmer has an additional wire lead. This “common” lead is connected to the common circuit wire. When replacing a standard three-way switch with a dimmer, the common circuit wire is attached to the darkest screw terminal on the old switch. In new switch wiring, the white wire should not supply current to the switched device and a separate neutral wire should be available in the switch box.