Our house is about 25 years old, though we have lived here less than 2.

Our master bath has a dual light switch, one for the main light bar over the sinks and one for the lights above the shower stall and tub. These are both oversized rocker switches with a slider to dim the lights.

If we leave the lights over the shower and tub on for an extended period of time - an hour or so - the switch will be noticeably warm to the touch. It does not seem to warm up any further by leaving it on beyond this. The wall switch does not have an internal backlight when it is off.

The lights on the circuit are an in-ceiling "can" light over the shower and a gaudy gold chandelier over the tub. Would replacing either of these help alleviate the problem?

I have not noticed this problem with the switch for the light over the sinks, though we don't typically leave that one on as long. This circuit consists of two bars of 6 bare-bulb globe lights each.

I am relatively confident that the switches are not original to the house, though the light fixtures themselves probably are. (Edit: Looked at them again this morning, and I'm less confident that the chandelier is original - the medallion is a slightly different color from the ceiling, so it either wasn't painted or was installed later.)

Should I be worried about the operating temperature of the switch?


It is perfectly normal for it to be warm. If it's HOT, you might be over capacity.

If there is more than one dimmer in a single box, you generally need to snap off the fins on the side(s) to get them to fit. With less heat sink surface area, they can't dissipate the heat as well, so the capacity is reduced. This is known as "de-rating."

In a nutshell, a typical residential dimmer rating works like this (For incandescent lights):

Both fins intact = 600W

One side fins removed = 500W

Both side fins removed = 400W

Here's a link to a typical manufacture's "manual" for one of these devices:


Top of page 1 - "Important Notes": Item 7 reads "It is normal for the Dimmer to feel warm to the touch during operation."

At the bottom of page two, there's a chart that shows de-rating info and ratings for other types of bulbs (non-incandescent)

That's as thoroughly and definitively as I can answer your question! There's also a toll-free number for Lutron at the bottom of that page. I believe they are the leading manufacturer of residential dimmers. dp

  • The "Diva" in that PDF looks like it's the exact one we have. Jan 20 '16 at 14:55

If this was a normal switch, I would say, no this is not normal. Since the switch does contain a dimmer, it is perfectly normal. Dimmers are electronic devices that do heat up. In fact, because of the heat they create, dimmers are rated for a maximum wattage. Special high wattage dimmers are available, and they even have integrated heat sinks to help dissipate the heat they generate.

That said, you need to calculate the total wattage of the bulbs you are controlling with the switch. If you have 6 bulbs, the max wattage you can use is probably 40W. A typical residential dimmer will have a maximum of 600W (yours will be labeled, probably on the face where its easy to see). Using 12 40W bulbs you have 480W, but using 60W bulbs you would be over-budget at 720W. This is important, because when you are over 600W, the dimmer will still work, but it could possibly get hot enough to damage itself or the wiring connections in the same box.

  • I will have to look. The chandelier bulbs are the mini flame style. 10 bulbs, but probably 25 or 40W each. No idea what is in the can. Jan 19 '16 at 14:56
  • Upon re-reading your question, it looks like the circuit with the two, 6-light bars (12 lights) is the one that doesn't heat up (is it a regular switch?), but the concept and calculations above are still valid - just figure your actual bulb count and wattage.
    – JPhi1618
    Jan 19 '16 at 14:56
  • The switches are identical. So I would expect that one to heat up just as much, if not more. But like I said, that might just be a function of how much we use them relatively. Jan 19 '16 at 14:58
  • 1
    That's entirely true. I have a similar switch in our bathroom, and I only notice the warmth when it's been on for a long time (after a shower, etc). You're probably OK - just double check the bulb wattage. Normally the dimmer will just burn out before anything else goes wrong, but you don't want to test it in your bathroom!
    – JPhi1618
    Jan 19 '16 at 15:00

I would say no, you should not be concerned about the operating temperature if the switches are only warm. It is normal for electricity to heat things like wires and switches that it is squeezed through. It always will to some degree. If you touch the prongs on the plug of a powerful vacuum after using for a little while they will likely be uncomfortably hot to the touch; unplugged before touching of course. If you're ever in a church or restaurant with normal switches instead of relays controlling big circuits of lights, the screws holding the switch plate/covers on might be hot enough to burn you.

Running 12 bulbs for an hour at 720 watts, 60 each assumed, is a decent load and the heating of switches is not surprising. Replacing with cfl bulbs could cut the load to under 200 watts and probably would eliminate the warming of the switch. The comfort cost of decent light being lost in a bathroom is high though. Never look quite the same in a mirror with monochrome or fixed wavelength light.

  • 3
    Hot enough to burn is pushing it - something is not right if that's the case. The line and contact impedance should not be so high as to produce that much heat under even full load. In the case of your vacuum or other high-draw appliance, it could be that the plug is making a poor connection. It could also be a deteriorating connection between the wiring and the outlet (especially common with aluminum wiring, push-style connections, or, (even worse) both). Outlets or switches that are too hot to touch would be a serious red flag for me.
    – J...
    Jan 19 '16 at 17:38
  • Agreed on hot enough to burn pushing it. Was not intending to condone the poor electrical jobs done in some restaurants and churches.
    – zerpsed
    Jan 20 '16 at 15:06
  • What would be considered 'too hot'? I put a digital cooking thermometer on a dimmer switch at max load and it registered top temperature around 94F when the ambient room temperature was below 70F.
    – JimmyJames
    Dec 3 '16 at 16:46

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