Help me NOT burn my house down (220V A/C content)

May moons ago (10+ years) I relocated out washer and dryer. I ran new wire and bought a new 50A socket. All has been well. About a month ago we get a used dryer, the plug on the new (to us) dryer wasn't the same as the plug on the wall, so I swapped the cables. The dryer has been working fine for over a month. Today my wife smells a burning smell. She said the outlet box was warm. I get home for lunch and have a look-see and see that things have gotten hot  right there at the side of the box.   

I pulled the cover  off and find the red wire got VERY hot. Upon closer inspection I found that the terminal was VERY lose.

I think the terminal WAS tight because you can see that the end of the wire was crushed by the screw. I don't know if the heat from the wire melted the plastic, allowing the terminal to get loose, or what.  If you look at where the screwdriver in the pic below is pointing, you can see that it was tight at one point.

The ground was tight and everything else looked good. The heat was only in the last few inches of wire.  

Here's the prongs on the plug, you can see that they got hot.

Any ideas? I'm surprised the circuit breaker didn't trip, that scares the heck outta me.

I am of not much help but I had something similar happen to me with my dishwasher plug/outlet. 

I believe the plug was not all the way into the socket and it was arcing/getting hot. The breaker never tripped. 

Could the plug not have been pushed in all the way in your case?

https://jag.smugmug.com/Miscellaneous/i-QLSHrnK/A

Pics there, no clue how to upload them. 

That looks like a classic case of a poor connection to me. Arcing causes heat which in turn melts the insulation. I'm thinking that screw connection on the right of the picture was made improperly, and even looks poor in the picture. It looks to me that the tab wasn't ever in the slot before the screw was tightened, but maybe it was undone before the picture was taken. Doesn't look like an overload to me, but rather a poor connection. I've seen a lot of these in my time. This sort of thing won't trip a breaker usually, as it's just heat, and not an overload. Dangerous none-the-less, but not usually something a breaker is designed to protect.

Edit: Also looks like you used plumbing pvc to run your conductors. Not an approved wiring method, and the lack of a terminal adapter is suspect as well.

I think you guys are right, bad connection. I'll het some proper conduit and terminal connectors when I fixify this. 

Thanks!

Looks like poor connection to me also.  Poor connection leads to arcing, carbon buildup, more resistance.  Resistance with current flowing through it is transformed into heat.  Hey, that's how the drier works too, but ON PURPOSE.  Anyway, replace the wires, replace the plugs, keep an eye on it and you should be OK.

And bonus points for not burning your house down.  Incidentally, that's why aluminum wire is not allowed in housing anymore.

Aluminum wiring is allowed as a service entrance conductor. Also it's an allowable method for large branch circuits like ovens and such. Heck it might even be allowable for almost any circuit in a residence, but I don't know where you could buy aluminum romex anymore. Devices are usually rated for copper or aluminum wiring, but maybe that's in case you run into an old wiring method that is aluminum. I'm not in the residential trade anymore, but I bet aluminum is not illegal, just not used much aside from what I have mentioned above. 

DrBoost said:

I think you guys are right, bad connection. I'll het some proper conduit and terminal connectors when I fixify this. 

Replace the entire receptacle.  It looks like the contacts on the wire that overheated are spread apart and possibly creating an arcing situation.

I just finished running the dryer after the repair. All's well. I moved the outlet up 10" so I could cut out all the wire that was hot. 

Thanks for the help