multiple dimmer switches in a single box


Old 03-11-05, 05:26 PM
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multiple dimmer switches in a single box

I have read (and physically observed) that dimmer switches get pretty warm and am wondering how to evaluate, and whether to be concerned, about a specific situation:

I have a 15 amp lighting circuit controlled by four dimmer switches in a single 4-gang box. I do not know the volume of the box so I can just say it appears "standard." When I remove the outlet cover, I can feel the warmth of the switches and also can see that the box is pretty crowded with 5 (I think) 14-2 NM cables: the incoming power plus four outgoing from the switches. This situation has existed for at least five years with no problems experienced, but I am wondering if this is a nonpermitted, or at least unwise, arrangement? Thanks.
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Old 03-11-05, 07:08 PM
Join Date: Jan 2004
Location: Oregon
Posts: 1,219
You are well to be concerned about this issue. As you have described things, you are _probably_ okay, but a little checking never hurts.

First, understand that heat is the bane of an electrical system. It causes terminals to slowly part, causes insulation to deteriorate, and generally causes the whole system to age and then fail. But at the same time, a certain amount of heating is to be expected and accepted in a properly operating electrical system. Dimmers produce heat and get warm. There is no getting around this. To keep the dimmers from getting too hot, they are designed to dissipate heat through their metal face.

The heat produced by a dimmer depends upon the design of the dimmer itself, and the total power being run through it. Each dimmer will be rated to operate a certain total lamp wattage, and will also have rating modifications set by proximity to other dimmers.

What you need to determine is the total wattage being run by each dimmer, and the rating of the dimmers themselves. You should just be able to read the light bulb wattages, and add them up, and for the dimmer you should be able to read numbers on the front face.

Most common dimmers are rated for 500W of incandescent lamp load, but have tabs that you need to break off when putting dimmers side by side. Each tab that you break off 'derates' the dimmer by in your case, I am guessing that the dimmers on the end are rated at 400W, and the ones in the middle are rated at 300W...but you should confirm this yourself.

If the wattage being controlled by each dimmer is less than its rating, then you should be in acceptable shape. Getting things to run cooler is _always_ an improvement; so even if you are within the ratings you may still want to consider upgrading the system. You can purchase more efficient (and more expensive) dimmers that produce less heat, or you could separate the dimmers into separate boxes, or you could replace some of the dimmers with ordinary switches.

Old 03-16-05, 05:13 PM
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Thanks, Jon, for the very clear and informative explanation. Your response indicates how, through dumb luck, I have not had any problems with this system. I didn't pay much attention to the ratings for the dimmers or the de-rating requirements that you mention but, fortunately, the light wattage controlled by each dimmer switch ranges from only 150 to no more than 300
watts. As you suggest, I will check the ratings for the specific dimmer switches that I have. These are Levitron slide dimmers with horizontal on/off switch at the bottom purchased at Home Depot for around $15 each. I suspect they are pretty standard and the ratings you mentioned are on target.

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