This picture was posted to de.sci.ing.elektrotechnik and I thought it might be interesting for you. The OP tried to hook up a 2000W heater to the 250V/10A rated receptacle and the result can be seen on the picture. This was not a cheap receptacle but a real expensive one that even once won a design prize. All this happened twice with receptacles of the same brand.
I have no idea. As you can see this was a backstabbed (or in this case sidestabbed) receptacle. They're fairly common in Europe, and many electricians will tell you these are far better than screw terminals. One guess in the original thread was that the terminals were rated for 2 conductors, but the spring pressure wasn't evenly distributed onto both wires, so one wire overheated. BTW, the more or less intact red wire is the phase jumper to the light switch above (not really visible in the pic). The badly burnt wire is the originally red feeder to the receptacle. I once saw a switch that looked like that, it had a black sooth trail all above on the wall, about half a meter high. Story back then was that the switch had come loose from the box (a known fact) and some ingenious students stuffed firecrackers into the box and pushed the switch back in. However, a short seems more likely to me (this was a bell button with a light inside), even though I'm not sure how that could have happened. After some time the charred switch was removed and the wires were hanging loose in mid-air, in a highschool main entrance. Don't know whether they were hot.
#136812 - 05/07/0310:22 AMRe: Smoky failure of a swiss receptacle
this is realy not a cheap one. It's made from www.feller.ch . I worked with them as an electrician in switzerland. It's good stuff. But the same situation was happend twice at my parents house. I don't know why. It is a combined element with a switch on the top. The second wire you see is the phase (hot wire) who is bridged to the switch.