I have a slide on the side 1000 watt dimmer with a connected load of 580 watts. The dimmer heats up hot to the touch. The dimmer in the same box for different lights is a 600 watt slide on side connected to 260 watts. does not get hot only warm that is normal. Anybody have any ideas why this is getting so hot?. I originally had a 600 watt in place of the 1000 watt. It got just as hot. Also the other dimmer is off when this happens. Thanks.
Some of the Lutrons I have had the same problem with. The aluminum fins on the side that are so difficult to fit into a multi-ganged box, and that you'll be tempted to break off to accomodate multiple devices in a box, lower the wattage rating when removed. I think I remeber the manufacturer telling me that you loose 100Watts capacity or more per side when you remove these fins.
Even with the fins intact, I have had to explain to a few clients that sometimes the dimmers just run hot when you have anything more than 350-400W running through them. I've even replaced a particular unit several times, and the heat factor remained the same (this one was a 600W unit passing 450W on full load).
If it's not a Lutron device or similar, I suggest you contact the manufacturer using the 1-800 number on the box or through their web site. They may have some tips on reducing the heat output on their particular model.
Bear in mind a dimmer drops at least .7v across the junction of the triac (maybe 1.4?). Multiply that times the number of amps the lights draw and you have the number of watts the device has to get rid of. (at 3.4 BTU per watt). A 600w light load (5a)will impose about 3.5 watts across the dimmer. That doesn't sound like much but if it is confined in a box it can still get pretty hot. Put a couple dimmers in a box and it can get real hot.
I had the same problem...1000w dimmer with a brass switch plate. It would melt your fingerprints! I called Lutron and they said this was normal and within specs. I added one of those insulating pads that usually go behind exterior outlet cover plates to cut down on drafts in the winter. It helped some.