Hot dimmer switch...

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Old 12-11-04, 01:45 PM
Twangler
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Hot dimmer switch...

Hi there,

This week I turned off the dimmer switch in our dining room and my finger touched one of the face plate screws. It was hot enough to cause me to pull my hand back.

I just replaced it with a new dimmer and this one began to warm up the screws as well - although it seems not as intense or at least as fast.

Is this normal and I didn't notice it before or should I call in an electrician?

Thank you,
Twangler
 
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Old 12-11-04, 01:59 PM
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It is normal for a dimmer to get warm. The more watts of light you are controlling the warmer it will get. The large ones actually have fins to help dispate the heat.
 
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Old 12-11-04, 03:16 PM
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Add up the wattage of all the bulbs controlled by this dimmer. Most dimmers are rated to control up to 600 watts, although 250-watt and 1000-watt dimmers are also available. If the wattage of your bulbs is greater than the rating of your dimmer, you are playing with fire (literally).

Warm is fine. Hot is not. Can you hold your hand on the dimmer face plate for a minute without burning yourself?

There are additional restrictions if this dimmer is not in an electrical box by itself. Is it?
 
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Old 12-17-04, 05:08 AM
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actually if you take a 600W dimmer and put 600W of lighting onto it and turn that dimmer up to full, this would be at the dimmers maximum. I would not expect you to be able to touch it. This is because many dimmers, at maximum, are UL listed to get up to 140 degrees above ambient which is the temperature of the room it is installed into at the front letal plate which is the heat sink for the dimmer.

So if this in a room that is at 70 degrees, your dimmer may reach temps of 200-210 degrees. Most people can barely keep there hands on anything above 150 for more than a few seconds.

My suggestion would be to either move up to the next biggest dimmer, provided you are not overloading the dimmer you have now (which will still create heat but just not as much) or replace your metal wallplate screws with nylon ones.

But definately do like John Nelson says and add up your lights to make sure you are not overloading it.
 
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Old 12-17-04, 08:07 AM
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Dim Bulb, that's a very interesting post. I would like to learn more. Do you have a reference for that 140-degree number you cited? The reason I'm worried is that the insulation on most wiring melts at temperatures lower than 200. Thanks!
 
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Old 12-20-04, 10:11 PM
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Originally Posted by John Nelson
Dim Bulb, that's a very interesting post. I would like to learn more. Do you have a reference for that 140-degree number you cited? The reason I'm worried is that the insulation on most wiring melts at temperatures lower than 200. Thanks!
House wiring does melt at 90C if in new wiring - correct however, on the dimmer, the front metal does not come in contact with the front metal plate. This metal plate (or yoke) is the heatsink for the dimmer. The dimmer utilizes a devices called a triac and it is fastened to the front of this dimmer so that the heat is passed INTO the room as opposed to into the box. Notice most dimmers have quite a large backbox to them.

Dimmers that use phase control, have always (at least for the last 40 years or so) used a triac and the triac has not changed since then so the heat has always been the same even when house wiring only needed to be 65C.

I hae not seen or heard of wires that have melted due to coming in contact with the metal yoke plate.

I have no online docs that I can reference you to unfortunately.
 
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Old 12-29-04, 11:37 AM
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Exclamation dimmers are rated?

please, to clarify:

if a chandelier has places for 5 lightbulbs, and each bulb used is a 60 watt bulb, then you've got 300 watts going, right? but if the dimmer is only rated for 250, an electrical fire could start?

"most" are rated for 600? if my house is 13 years old, is it "probably" a 600?

if i take the plastic face plate off my switch, will it say somewhere what it's rated for?

(i've got a "warm" dimmer also....... )

thanks!
 
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Old 12-29-04, 08:07 PM
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Yes Annette, the hypothetical situation you describe is a fire hazard. But you described your dimmer as "warm", so it's probably not your situation.
 
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