Waaaaaaay back in the 60's I used to service an electronic accounting machine for NCR ( then National Cash Register ) called the 395. This machine had an option of a card reader to read IBM type punch cards.
The cost of acquisition back then was somewhere in the 20-30K range.
There was a switch adjustment that had to be made in the reader on a dual section switch, one section had 115 A/C, the other had 5V DC.
This adjustment had to be made with power on and the reader cycling.
If you were stupid enough to use a regular screwdriver for this adjustment, you COULD connect the 115 AC to the 5V DC.
NOW, THAT'S WHAT I CALL A SHORT.
Smoke would come from more places than you could count, and you were looking at at least a week of soldering in new transistors.
This was in the days before printed circuit boards.