How to Install a New Dimmer


With a dimmer, you can adjust light levels to create just the right lighting to suit your mood and enhance your home's atmosphere. Equally important, dimmers save energy and make bulbs last much longer than they would at constant full power.

Things You'll Need

  • Neon Tester
  • Dimmer With Wire Nuts
  • Screwdriver
  • Wire Cutters/strippers
  • Shut off the circuit at the main service panel and remove the housing over the switch. Unscrew the switch and lift it out. If the box is metal, be particularly careful not to let the screw terminals on the side of the switch touch the box.

  • Test for power with a neon tester, probing one switch terminal and the bare grounding wire; repeat the test for the other terminal (see A). Proceed if the test light doesn't glow.

  • Cut off the wires at the switch terminals using wire cutters/strippers, and strip about 1/2 inch (12 mm) of insulation off the two cut switch wires.

  • Wire the dimmer. A dimmer with two black wires has no polarity, so twist each dimmer wire together with either one of the switch wires and screw on a wire nut (see B). If the dimmer has a green wire, connect it to the grounding wire.

  • If a dimmer has black and red wires, wire the black one to the incoming power (line) and red to the lights (load). To identify the wires, pull both switch wires out of the box; if you have a plastic outlet box, pull out the bare wires, too. Keep them well apart from each other. Have someone restore power. Use a neon tester to probe one switch wire and the bare wire (or the metal box). If the tester glows, that is the line, and the other wire is the load.

Tips & Warnings

  • Make sure the dimmer is rated for at least the maximum rated wattage of all the light fixtures it will control.
  • If two switches in different locations control a light, only one of them can be a dimmer switch.
  • To replace a three-way switch, attach the common lead to the wire connected to the darkest screw on the old switch.
  • Only fluorescent lights with special ballasts can be dimmed; low-voltage lighting requires special dimmers.

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