I was working in one of our big glass house government computer centers in DC (4 water cooled systems, national network of users). We had a new 60a 3p Russell Stoll that was phased wrong. This customer insisted that we not change our equipment, they wanted everything phased the same at the plug so they called the GSA "electrician/handyman". He dragged himself in there several hours later. He looked at the wiring in the panel and all the colors lined up so he said it must be wrong in the plug. We asked if he knew what to do and he said "sure, just swap two of them". We went back to what we were doing and let him work. After a while he said we were ready. He matter of factly flipped the breaker and fire shot out, smoke and such. The whole room went black and the emergency lights came on along with several alarms. They managed to abort the Halon and get the alarms reset while he went downstairs "to check the main". In about 20 minutes (not bad for government work) the lights came back and the systems started powering up. Operators on all the consoles were furiously trying to get all the systems back up. Everything seemed to be working except the stuff on that 400a panel where the fault was. Mr happy showed up with a cup of coffee about 20 minutes later and asked how it was going. The data center manager was hollering about the 10 boxes that didn't come up and Mr H walks over and says, "No Problem it's just the 400a breaker tripped". He flips it. Boom! Fire smoke and darkness. By now we decided we better jump in there while he was on his quest, so I started working the original 60a breaker back and forth until I broke loose the welded contacts taped it open with a do not operate tag and flipped the 400 back on. In a few minutes the power came back on and we had everything but the original 60a going. They started IPL'ing again and Mr happy shows up again feeling very proud of himself that everything is working. I told him about the bad breaker and he says he had never seen anything like that before. The DC manager was still steaming watching this all transpire. When the handyman reached up to flip the 60a because he didn't believe me they tackled him and dragged him out!
The next morning when the real electrician showed up, we found the guy had swapped one phase with the EGC!
I am still not sure why this also tripped the main but I am guessing they were probably at about 99.8% of the rating.
