Eric and I are doing some remodel work on a house in St. Louis. (See my previous article here)
He was working on the kitchen while I was in the basement pulling out old, unneeded circuits.
Right under the panel was an old-style dryer receptacle.
The receptacle was discolored on one of the terminals because it had arced.
I was taking this circuit out of the panel anyway so I opened the device to see what was going on.
The hot terminals are both corroded.
Rust is not a good conductor. (Neither is oxidized aluminum if you have any of that wiring in your house).
The wire on the left overheated because of the rust and at some point failed causing an arc.
If you have an old, stone basement, it is a good idea to keep a dehumidifier running to help prevent accidents such as this.
Images taken by me.