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Old 02-28-2011, 09:36 AM   #1
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Dimmer switches and gang boxes


I am installing recessed lights in a basement that had hanging fluorescent lights on one 15A circuit. The plan is to have two banks of lights controlled by two dimmers. The first bank will be 600W and the second bank will be 800W. My hope was to mount the two dimmers in a triple gang box with one regular toggle switch (on a separate circuit) which will control the lights on the stairs. Basically the idea is that at the bottom of the steps there will be three switches, one dimmer for one side of the basement, one dimmer for the other side of the basement, and one toggle for the stairs. My concern is heat buildup. Given the fact that there will be three switches in the box (albeit one not a dimmer) should I just use two 1000W dimmers to compensate for the necessary de-rating?

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Old 02-28-2011, 02:22 PM   #2
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Dimmer switches and gang boxes


I cannot speak to heat from two dimmer switches in a common box, but in regard to the circuit, I believe that in the U.S. you are restricted to 80% capacity on a lighting circuit, in which case you would need two 15 amp circuits for the recessed lights, which is probably a good idea anyway, so that you can work on one circuit and still have lights, or go to a 20 amp circuit.

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Old 02-28-2011, 02:49 PM   #3
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I cannot speak to heat from two dimmer switches in a common box, but in regard to the circuit, I believe that in the U.S. you are restricted to 80% capacity on a lighting circuit, in which case you would need two 15 amp circuits for the recessed lights, which is probably a good idea anyway, so that you can work on one circuit and still have lights, or go to a 20 amp circuit.
The 80% rule only applies to continuous loads (residential lighting is not considered continuous), so it doesn't apply in this case. Plus though the cans are rated for 100W each they'll have 15W dimmable CFLs anyway.

The maximum load with 14 cans @ 100W each would be 1400W:

1400W/120V = 11.6A (still a hair less than 80% of 15 anyway)

Actual load will be 14 cans @ 15W each:

210W/120V = 1.75A

The outlets of course will be on a separate circuit so even if I needed to do work on the lighting circuit I could just plug in a work light. Now, anyone have an idea on the dimmers?
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Old 02-28-2011, 02:53 PM   #4
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Dimmer switches and gang boxes


You do need to derate dimmers for more than one in a box. The dimmer directions will tell you how much to derate them for more than one in a box. If you put the switch in the center of the two dimmers you might not need to derate them.
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Old 02-28-2011, 02:56 PM   #5
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If you put the switch in the center of the two dimmers you might not need to derate them.
Duh...never thought of that! Thanks! I was only thinking in terms of having the two banks next to each other since that was the most intuitive approach, but I suppose have a more symmetrical switch panel (dimmer, toggle, dimmer as opposed to dimmer, dimmer, toggle) might look better too.
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Old 02-28-2011, 03:19 PM   #6
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Mount them as Joe said, but use 1000W dimmers. If the loads are as you originally said (600W and 800W), you will need the bigger dimmers anyway.
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Old 02-28-2011, 03:30 PM   #7
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The 80% rule only applies to continuous loads (residential lighting is not considered continuous

Well, Badfish, you obviously had never met my kids!! Another continuous load was the television.
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Old 02-28-2011, 06:14 PM   #8
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The 80% rule only applies to continuous loads (residential lighting is not considered continuous), so it doesn't apply in this case.
Thank you for clarifying this for me. My time is spent approximately 50/50 between residential and commercial, and although I have a pretty decent working knowledge of electrical applications in both, I am not an electrician, so obviously had the facts twisted a bit.
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Old 02-28-2011, 06:41 PM   #9
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Dimmer switches and gang boxes


Actually if the switch is the main lighting control then you might want it to be the one closest to the door so it is easily swiped on/off as you enter/leave the room.
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Old 03-01-2011, 09:55 AM   #10
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Badfish, if you are using CFLs try the Lutron C•L dimmers. They have a much better dimming range and won't cut out or strobe at low end. http://www.lutron.com/Education-Trai...LsandLEDs.aspx

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