Dimmer Switches

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I have a dimmer switch on my dining room light. I just noticed that’s warm when I touch it. Is this dangerous?

A dimmer switch that's warm to the touch is usually a sign that it is overloaded. Chances are that you have exceeded the wattage rating for the switch.

Most dimmer switches are designed to handle about 600 watts. If you have a light fixture with several bulbs in it, add up the total wattage of all the bulbs and it should be under 600, preferably less than 550. Using a dimmer switch to control more than 600 watts can cause the switch to prematurely fail or in some instances may cause heat damage or melting of the wiring.

If you must dim more than 600 watts, consider upgrading to a high powered dimmer switch. Several models can handle up to 1,500 watts. Of course, check the wiring to make sure it can handle this big of a load. If in doubt, contact a licensed electrician first.

Can I install more than one dimmer switch in a multi-gang box?

Yes, this is allowed. However, keep in mind that when installing two or more dimmers in the same box, the wattage capacity of each dimmer must be derated. The amount to be derated is different with each dimmer and is found either on the installation instructions, or printed on the dimmer itself. Typically, a wattage reduction of 10% is common.

The reason for the reduction is that when two or more dimmers share the same box, it’s harder for the heat generated by each dimmer to be dissipated. A hotter running dimmer switch will fail prematurely if used at its maximum wattage rating.

I recently installed a dimmer switch in my son's room. When I turn the light down to low, it gives off a faint whistling sound. Any ideas?

There’s a couple of possible reasons for this:

1. The bulb you are using is not incandescent. If you are using a compact fluorescent (CFL), or a low-voltage type bulb, then it will eventually fail prematurely when used with a standard dimmer. They make magnetic dimmers (for low-voltage lights) and dimmers that work with CFL bulbs, although I've found the CFL dimmers not to be too reliable.

2. You are using an incandescent bulb, in which case the noise is just a reaction of the filament to the lower power running through it. Sometimes changing to a better quality bulb may eliminate this problem.

3. Are you trying to dim anything other than light bulbs? for instance, is there a ceiling fan working on the same switch? Fans need to be controlled by a fan speed switch, not a dimmer, or you risk damaging the fan motor.

4. Lastly, make sure that you are not exceeding the capacity of the dimmer. Most can handle up to 660 watts, but there are some cheaper ones out there that have problems with as little as 120 watts. One indication of this is that the switch plate will get very hot when it is running in a dimmed mode (note that plates will usually get warm; this is not a problem).

I’m replacing a 3-way dimmer. The replacement switch has a ground wire, the one I am replacing doesn't. The switch is in a large metal box with 2 others. I can see a copper ground wire in the back of the box, but can't get to it. Can I snip the ground off the new switch?

No, you need to ground the switch. You can either dig out the ground wires in the back of the box and connect the switch ground to them or you can connect it to the metal box. This is done either with a ground clip or a grounding pigtail with a captive screw attached. They're available at Home Depot or Lowes, or your local electrical distributor.

I have a lamp that flickers when I turn the dimmer switch all the way up. I’ve changed bulbs but the problem persists. What else should I check?

Some older style rotary dimmers contain an internal contact arm that moves along a potentiometer. Over time, dust and debris tend to settle on the windings and this causes an intermittent contact of the wiper arm which can cause the flickering. Usually the easiest solution is to replace the dimmer switch and the problem should go away.

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