I recently installed three pendant lights in my kitchen. I wired them parallel and put them all on one dimmer switch. However, when I turn on the lights, I hear a high pitch hum which seems to dissipate when I turn the dimmer switch to the brightest level.

Can anyone tell me why this humming sound is happening? It is very annoying.

You might need a higher amp(?) switch. What's the total wattage of the lights... and what is the dimmer rated for?

I could be wrong, but I had a similar issue and put in an expensive switch and lowered each bulb to 60 watt. It went away.

I'd swap out that dimmer for another brand or style. I doubt that you are over loading the current dimmer but compare your wattage X 3 and insure you are below the dimmers rating. Some types of dimmers are more prone to noise than others.

You aren't using any compact fluorescent bulbs are you? Many of them will really sing when you run them on a dimmer. DON'T do that! It is dangerous. You ought to look at the current waveform of a dimmed twister bulb!

Some regular incandescent bulbs will sing when dimmed because of how the filament is mounted and what the dimmer does to the electrical waveform. When the bulbs are noticeably dimmed the leading edge of the sine wave is "chopped off" and there is a very abrupt switching to some intermediate voltage level on the wave. The magnetic action on the coiled filament causes it to move in a way that a normal sine wave wouldn't. You hear this as a high frequency ringing. You also lose some of that bulb life that the dimmer marketers try to sell you.

Incandescent light bulbs hum when filaments vibrate. Using a lower wattage or different brand bulb will usually prevent or reduce light bulb hum. I have had good experiences with 130V bulbs, or rough service bulbs. Also I agree and disagree with EPMiller you should never use ordinary CFL bulbs with incandescent dimmers, however there are CFL bulbs available in dimmable models. I have attached a site that sells them, but you can also purchase these bulbs at your local hardware store. bulbs.com - Results Just be sure that you are using the correct dimmer for the type of bulbs that you choose.
Let me know if you have any additional questions.:cool:

Tommy is right about the filaments. Cheap lamps, even name brand ones, have very little filament support, so the filament vibrates so much that you get your hum or buzz.

Higher quality lamps or "long life" lamps usually have more supports to the filaments, hence the longer life.

The new crop of "ceiling fan lamps" work good as they are made for a higher vibration environment.

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Originally Posted by thommyschnak

<snip> I have had good experiences with 130V bulbs, or rough service bulbs. Also I agree and disagree with EPMiller you should never use ordinary CFL bulbs with incandescent dimmers, however there are CFL bulbs available in dimmable models. <snip>

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Just remember, when you use rough service or 130 volt bulbs you will get less light for your electric consumption. It is significant, we have measured some at greater than 10% fewer lumens/watt than a regular 120v bulb.

Also, use your dimmer only for occasional use. When dimmed, a light bulb's light output falls off much faster than it's current consumption. I have measured up to 30% (of full draw) current consumption on a bulb that wasn't even putting out 1% of it's light. Put in the lowest wattage bulbs for the light you need and leave the dimmer set on high as much as possible.

As to the dimmable CLFs, yes, I know they are out there but not very many or for reasonable prices. Most people don't even know they exist or what the difference is. Thank you for bringing that up.

EPM