As part of our house upgrade, I bought an new dryer. I thought I would use the 240v plug from the old dryer. Three of the wires had been properly installed, but the forth red wire had been installed using a cheap bolt and nut. They had rusted together and I had to break the bolt with vice grips to disconnect the wire. As the picture shows, the poor connection had caused the red wire to heat up to the point that the insulation had melted into a blob, leaving damaged exposed copper wire. It never smoked or started a fire, and I don’t know how long ago the damage started occurring, but I had to buy an new 240v plug for the new dryer. So far the new dryer is working fine.
