Replacing a standard single-pole or three-way switch with a dimmer switch is no different than replacing a standard switch. Remember: Dimmer switches don’t work on most fluorescent fixtures, and low-voltage lighting requires special low-voltage dimmers.
Check the rating of the dimmer switch you purchase. Most dimmer switches can handle 600 watts of power. Count the number of light bulbs that the switch controls and add up the maximum wattage bulb allowed for the fixture. For example, if the switch controls a light fixture which accommodates up to two 100-watt bulbs (200 watts total) a 600-watt dimmer will have no problem, but a string of seven recessed lights could overload the dimmer.
To replace a standard switch with a dimmer switch, follow these steps: Turn off the power to the switch at the circuit or fuse panel.
Unscrew and remove the switch plate; then use a voltage tester to make sure that the circuit is dead.
Unscrew the switch from the electrical box and pull it out with the wires still attached.
Remove the wires from the old switch. Dimmer switches are usually connected to the house wiring by short lengths of wire coming out of the switch body rather than by screw terminals.
Use the connectors (wire nuts) supplied with the fixture to attach theblack wires coming out of the dimmer switch to the colored wires that were attached to the terminals on the old switch. First, twist the wires together, and then screw on the wire nut.
Push the new switch back into the electrical box and screw it in place. The body of a dimmer is larger than the switch being replaced. Don't just force it in. Often, you need to reposition or better organize the wires first to make room for it.
Screw on the switch plate.
Push the control knob, if there is one, onto the shaft protruding from the switch.
Turn on the power.