3 Dimmer Switches In a Box

Originally Posted By: pbennett1
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How many is too many. The condo I inspected had three, and was hot to the touch?


Originally Posted By: Jay Moge
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I’m head maintenance for a companie that has condo style apt. currently renting in mass. some tenants put dimmer switches in the box that normaly controls 4 fixtures (4 switches). depending on the fixture the switches may get hot. like if they put a dimmer on the ceiling fan, which the manufacturer tells you not to do, than you get heat. same with florecent. eccept they just won’t work at all and heat the switch. was there any of those (fan or flo.) on the dimmers?


Originally Posted By: Greg Fretwell
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The real answer is probably in the manufacturers instructions.


Usually if the heat sinks overlap in the box it is too many.


From a practical sense it will really depend on what load is on the dimmer.


They all tend to be a little warm, basically about 6% of the load in watts.


If you had three 600 watt dimmers loaded to 1200w, that would probably be too much in a box but if there was only a few hundred watts of connected load there wouldn't be a problem.


Originally Posted By: Jay Moge
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About how much amps. are there in a ceiling fan thats resisted by a dimmer but still trying to draw enough power to spin at a certian speed? icon_confused.gif


Originally Posted By: lgoodman
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Rheostats are different from dimmers. Dimmers are not used for motors. Rheostats are used for motors. Rheostats can be used to dim lights.


Watts divided by volts equals amps. If electricity were that simple then cutting the volts by half would double the amps.
But I don't think that amperage doubles when the speed of the fan is halved because I don't think we are really cutting the voltage. I think we are just consuming fewer watts and the amps drop slightly at lower speed because fewer watts divided by the same voltage equals fewer amps. On top of that the amps are probably fractional and would hardly be a factor in anything important.

I am willing to be educated on this subject


Originally Posted By: Greg Fretwell
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Leigh I am betting you are not old enough to have seen a rheostat on a motor. (A pure resistive dimmer)


These dimmers and variable speed motor controllers are all solid state. They work by chopping out a chunk of the sine wave. In the case of an incandecent dimmer it is really ugly. They just lop off the leading edge until the SCR or triac triggers then the light sees the last sliver. It can be a spiky nasty waveform, the cheapest of which, will make a radio hum.


That works fine on a regular light bulb.


The only energy imposed on the dimmer is the .7 v voltage drop across the silicon junction.


When you move up to an inductive load like a motor in a paddle fan they need to clean up the wave form or they get all sorts of reflected energy in the circuit That will cause the motor and the dimmer to burn up. They do make fan rated diommers but you need to be sure they are using one.


Originally Posted By: lgoodman
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Greg,


Thanks for that. I’ll change my terms to “dimmer” and “motor controller” to diferrentiate between their purposes. Am I correct that dimmers are not properly used as motor contollers, or has that changed?


I agree that most motor contollers are solid state now, but for some reason I had not changed my terminology in refering to them.

Rheostats are still around, of course. Theatrical lighting is rheostat controlled because eliminating extraneous noise (that hum) is important to the presentation.

I'll take the bet, though. I'm 59 and I still occasionally call the refrigerator " the ice box "


Originally Posted By: Greg Fretwell
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That’s funny, you look a lot younger. icon_wink.gif


A agree you might see rheostats in old theater installations but I suspect that has more to do with the reluctance of stage electricians to change than the technology. If you buy a high end dimmer it will tame those sharp corners off the wave form and the hum from bulb filiments will be minimized. Some bulbs still seem to have a ringing problem.
I am not sure exactly what the magic is in the fan controller but I do know they work pretty well.

The fan "dimmers" will look pretty much the same as a light dimmer, until you look at the price tag.