A story I was told on a course was of a Ptarmigan Switch in Bosnia. During a power change, AC was cut and the Switch ran on DC (2 or 4 batteries) until the AC was moved to a new generator. As part of the procedure, you had to manually power back on the ACU.
The story goes that the power change was done and the equipment was back on AC but with no ACU. Someone went into the box body to find it dripping with water, having had no dehumidifying for some time. Not great for electronics. They started the ACU and left it for a few days and it dried out, never stopping working once.