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Electrical: Adding Dimmer Switches

Sometimes the lighting in a room is just too bright, but without it, the room is too dark. In most cases this problem can be overcome by replacing the standard wall switch with a dimmer switch. The first step in adding a dimmer switch is to calculate how much “load” the switch will have. Most dimmer switches are designed for a maximum of 600 watts; so if your load is greater you’ll need a dimmer for that load.

To calculate load, simply total the wattage of all the fixtures or bulbs that the dimmer is to control. For instance, if the dimmer is to control a fixture with 6 bulbs of 60 watts each, (6 x 60 = 360 watts total) a standard 600 watt dimmer will be fine. Overloading a dimmer could pose a hazard and will cause the dimmer to fail prematurely. (If you are installing more than one dimmer in the same electrical box, check the manufacturer’s recommendations to see if the allowable wattage is reduced because of the extra heat generated in a side-by-side installation.)

Most dimmers are designed for incandescent lights, that is, standard light bulbs. If you wish to control fluorescent lights or ceiling fans, you’ll need a special dimmer. Also, there are now special compact fluorescents that are made for dimming. Check the manufacturer’s recommendations and with your local home center or electrical supply house for the proper dimmer or bulb.

Electrical testerOnce you are ready to install the dimmer, turn off the circuit breaker that controls power to the receptacle. Once the breaker is off, I use a simple tester to confirm that the circuit is no longer hot. If you have difficulty determining whether or not the power is off, turn off the main circuit breaker; but have a flashlight handy.

Next, remove the old switch. If the switch is typical with a black, white, and ground wire, it’s a standard single pole switch. If, however, the switch is one of two that control the same light, it’s a 3-way, and will have 3 wires plus the ground. Three-way switches must be replaced by 3-way dimmers, and you’ll choose only one of the switch locations for the location of the dimmer. If you want to replace both switches with dimmers, you’ll have to purchase special dimmers that are considerably more expensive.

Once you have purchased the correct dimmer switch, replacing it is similar to replacing a standard wall switch, except the dimmer will come with wires extending out the back. After you remove the wires from the old switch, you must either straighten the ends where they were attached to the switch or clip the ends off and strip about ½” insulation to expose sufficient bare wire to connect to the new switch wires.

Wire connectorsYou will use wire connectors or nuts to make the new connection. These should have a metal insert for the best connection. I never use the cheap plastic ones without the metal core. Begin by twisting the ends of the switch wires into a tight single strand and place it next to the wire from the electrical box that was removed from the old switch. Green dimmer wire connects to the bare ground wire, and each of the two remaining wires connect to the two remaining wires from the wall box—just connect one dimmer wire to one of the old switch wires and the other to the wire that remains.


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