Back in the day I installed a buss system to improve power delivery to racks in our local data center. There were two separate 240v/100A busses with tap boxes that would drop the appropriate twist-lock receptacle to each rack - some 120v, some 240v. I'm not a licensed electrician, but I mounted the busses and built all of the tap boxes. The electrical company that we worked with at the time inspected everything and made the connections to primary power. We fired it up and everything was good. As we moved racks into places, I twisted in the pre-built tap boxes above them and connected the power feeds to the twist locks. No issues. One day, we moved a new rack in and as I started to twist the tap box into place, BOOM. Melted copper rained down the back of my head, neck and back, burning me slightly (along with my shirt) until it pooled on the floor and melted the tile. Turns out the insulation between a pair of the legs was faulty and it was no different than throwing a wrench across the phases when it hit the buss conductors. I was lucky. In the picture, the tap box in the background is what the connectors should look like, although it got smoked as an innocent bystander. Don't fuck with electricity, kids...