My desk was moved across the room. The raised flooring had power and networking in tanks. Site services moved the box across to the new position, removed the tile that was there and rammed the tank into place. I didn't see them do it, but I'm pretty sure that they had used a lot of force, because they had rotated it 90° and when I plugged in my PC and turned it on, a huge spark shot out the back and smoke wafted out of the fan grill.
Somehow they had managed to swap live and earth and it go BANG! It is a shame I didn't turn the monitor on first, because it was blurry and flickered... Hey ho.
Another time, a DEC engineer came out to do a memory upgrade on a Vax. There were several machines in a row. They moved all the jobs to the next one, ran the shutdown sequence and the DEC engineer disappeared behind the Vax to throw the mains switch on the wall. Only he "missed".
The ops at the terminal looked up from the console with a puzzled look as he reappeared, whilst screams started emitting from the next machine in the line - the one that had received all the jobs and users from the machine being shut down. Yep, you guessed it, he threw the wrong switch!