How to Install a Dimmer Switch

Dimmers are addicting. Once you install one, you'll want more. For just a few minutes' work, you get the ultimate in mood lighting. The romantic use of dimmers in dining rooms and baths is obvious to even the dimmest of bulbs. But you'll also appreciate dimmers when you go downstairs for that 3 a.m. snack and your sleepy eyeballs aren't seared by the usual prison-camp glare of kitchen lights. In other words, dimmers let you use existing fixtures as nightlights.

They save money, too, dramatically increasing bulb life while reducing electricity use. According to one industry source, dimming an incandescent bulb 10 percent can save 5 percent on electricity and double the bulb life. Dimming it 50 percent saves 25 percent on electricity and extends bulb life 20 times.

Replace a switch that controls a light or lights from a single location with a single-pole dimmer. Replace a three-way switch with a three-way dimmer.

Step by Step

1. Turn off power to the circuit, and test the circuit to be sure it's off. Unscrew the plate covering the switch and the screws holding the switch in its outlet box. Gently pull the switch out of its box.
2. Disconnect the old switch by unscrewing the wires that had been attached to it. Straighten those wires and, if necessary, snip the ends and strip the wires afresh.
3. Connect the dimmer. Most dimmers have two non-color-coded wire leads instead of terminals. Most don't have a grounding wire. Pair the dimmer leads with the house wires, one to black and the other to white (or you may find a white wire marked black).

   If you're replacing a three-way switch with a three-way dimmer, before you disconnect any wires, note which wire attaches to each switch terminal. The easiest way to keep things straight is to attach a piece of masking tape to each wire and write, on the tape, what that wire was attached to. Attach those wires to the corresponding traveler terminals of the new three-way dimmer so they match the wiring of the old three-way switch. (Don't worry, it's easier to do than to explain.)

   Splice the wires with the twist-on wire connectors supplied with the dimmer.

4. Gently fold all wires back into the box by pushing evenly on the dimmer. Screw the dimmer to the outlet box, replace the cover plate and then press the dimmer dial down into the shaft of the dimmer. Turn the power back on, and you're ready for business.

Buying Advice
A dimmer may hum if it's controlling more bulbs than it's designed to handle. Be sure to buy a dimmer with a wattage rating greater than the total wattage of the bulbs it will control. If a bulb hums, replace it with a heavier-filament, rough-service type.

Safety
Never use an ordinary dimmer to control a receptacle, fluorescent light or any appliance that has a motor (such as a ceiling fan) or transformer (such as low-voltage lights). Those devices are designed to run at certain speeds; when forced to run more slowly on reduced current, they may overheat and get damaged. You may also destroy your dimmer in the process. Fluorescent lights require three-wire cables and expensive dimmers.