Light Switch getting very hot

CletusTSJY

I recently bought a house and after a month I noticed that the light switch in the kitchen, which is a dimmer with an on/off switch, gets very hot when the lights are on for more than about five minutes. Almost hot enough that it would hurt to hold your hand on it. Specifically, the metal around the outside of the switch is getting hot. I bought a new switch, the exact same kind of dimmer except this one said 600W instead of 300W, installed it and found the exact same problem. Any idea what's going on? Would replacing it with a standard light switch take care of it?

Yoyizit

1 You are abusing the dimmer by dimming something that is not supposed to be dimmed.
2 Almost certainly, Yes.

CletusTSJY

Thanks for your reply. That is weird, the dimmer was installed when we bought the house and the only thing I've done is replace a burnt out lightbulb with another lightbulb that came from the living room- which also has a dimmer! Well I will replace it with a regular light switch...not like I need romantic lighting while cooking my top ramen! :P

Thanks again!

Scuba_Dave

If you are dimming just incandescent lights it should work as long as you stay under the rated wattage
A heavy metal face plate can help dissipate heat
I use the biggest electric box possible for everything
This gives it more air space
Some of the small plastic boxes & older metal boxes are very small

Yoyizit

This is puzzling, if they are incand. lamps.
I guess while you're changing it out you could check the current draw with a clamp-on ammeter.
Maybe there is an overload that
never goes to a short circuit and
never clears, either,
but this is probably unlikely [probably improbable?].

CletusTSJY

Interesting. If that is the case, replacing it with a regular light switch will not fix the problem I'm guessing? Will the regular light switch get hot too?

I did have to really cram the wires into the box just to get the switch close enough to screw it in...could it just be that there isn't enough room inside the box to dissipate the heat? It shares a box with the dining room light switch (which is not a dimmer and never gets hot) and it's pretty crowded in there.

Yoyizit

A regular light switch dissipates ~0.3w, max, and a dimmer, 5w. This few watts spread out over the several sq. inches of surface area of a dimmer shouldn't be very hot.

Crowded or not, I've never had a dimmer that did that.
I guess you could take it out of the wall box and run it for a while in free air. Within 5 minutes or so you'll know if it's still going to get hot.

A bad wirenut connection could also dissipate 5w, but the surface area of a wirenut is so small that the temp. would be too hot to touch.

I suppose a yet-to-be-discovered root cause could have clobbered both dimmers, or
both off-shore-manufactured dimmers were bad from the factory.

Grimlock

It is common for dimmers to get warm. If you find that you can't touch it because it is so hot then you most likely have an overloaded dimmer. Count the watt labels on all of your lamps, add them up and compare to the dimmers rating. Some dimmers have tabs on the side that can be removed to allow them to be ganged up next to other large devices, if these tabs are removed than the rating goes down (Look on the dimmer). If you are pushing the load close to the max then you can expect it to get a little more than warm.

EDIT: No normal toggle switch should get warm/hot unless there is a problem.

CletusTSJY

Thanks for everyone's help. I put the cover back on the dimer and turned the lights on for a few hours to see how hot the cover and screws got. Although it's still warm, it is definitely much cooler than it was with the previous dimmer. I added up the wattage of all the light bulbs and it came to 390 watts. The previous dimmer said 300 watts on it, and the documentation I read said if there's another switch in the same box, the number of watts it can handle goes down. If that's the case, I'm thinking the dimmer was getting overloaded? This new dimmer is 600 watts and with the extra switch in the box, it comes down to 500 watts, which is still greater than the 390 watts that the bulbs add up to. I'm going to stick with this and see if it ever gets too hot.

Thanks again for everyone's help.

Jim Port

The dimmer would only need to be derated if installed next to another dimmer and the breakoff tab(s) were removed. Installed next to a regular toggle switch does not affect the dimmers rating.

All dimmers generate heat. See this FAQ fron Lutron.

http://www.lutron.com/default.aspx?pid=6#faq6

IIRC the temperature may get to 140 degrees depending on load and amount of dimming.

Yoyizit

2% [from the link] of 600w is 12w, dissipated in the volume of a 25w bulb. That's fairly warm, but my dimmers don't run anywhere near capacity.

Adults can be burned in 5 sec at 60°C(140°F).

kbsparky

A hot glue gun only uses 10 watts or so, and those are too hot to touch.

A dimmer with a plastic wall plate (plastic is an insulator) held with metal plate screws can make hot spots out of those screws. The equivalent of touching the nozzle of a plugged in glue gun.

Get a heavy, metal wall plate to help dissipate the heat.

__________________
-KB

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skidrowpete

was at a nursing home and older residents were complaining about hot dimmer plates manager wanted them changed but that would not have been cost effective called leviton and talked to engineer and to my disbelief he quoted me the temperature could be as high as 80-90 degrees or about i67 degree c. the only way to cure that was to install regular snap action switches or convert them over to a tmo gang box and install a higherr rated dimmer with heat sinks made in them

Scuba_Dave

I don't really find 80-90 that hot
Body Temp is hotter then that

Yoyizit

You mean 80C = 176F?

With all the NFPA/NEC rules and regs I can't believe these dimmers pass muster.