Here is a photo of a 120 VAC plug that was providing power to three equipment racks in the engineering area of a radio station.  The cable-to-plug wiring developed higher than normal resistance resulting in overheating.  The insulation on one conductor turned brown from the heating.  As you can see, the plastic on the plug suffered as well.  The problem was caught on a routine inspection when it was noticed that the plug was running hot.  This plug would have gone into total failure after not too much longer.  The wall outlet didn't look very good either.