I was working once in a huge "glass house" computer room that was fed by a 1600a 3p wye. They had 2 big water cooled MP systems with about 1000 remote users and the local batch work. (NIH Bethesda) These guys never shut down. In those days the power whips under the floor were Russell Stoll plugs on SO cord. Sometime around 75 someone decided these all had to be FMC but nobody makes a connector that attaches FMC to a RS receptacle so they pull out leaving the plug hanging on THHN. Well they were swapping the room over one 400a panel at a time while the customer was still up. Somebody yanked on one of the SO cords and we had a flash/bang under the floor and the room went dark. People were losing their mind and they put in an emergency call for "the electrician". By the time the GSA "building electrician" (also plumber and trash can tech) showed up we had isolated the problem to one 400a panel and had that main turned off. He went downstairs and cranked on the 1600a breaker. The room came up and they were furiously working to get the systems up and back online. By the time he got back up there they just about had everyone online. We told him the tale and he immediately said we must be wrong and flipped on the 400a breaker... Boom ... dark!
By then the DP manager was bouncing off the ceiling. Dummy goes back downstairs and cranks on the breaker again. In the mean time we had found the FMC that shorted and just had that 60a 3p turned off. The whole room came back up and they started IPLing again. Dummy shows up in the computer room again, we show him the breaker that was causing the problem, tell him about the FMC and the connector, he again tells us we are full of crap, That can't be right, flips the breaker on and BOOM.
The data center manager called security and told them "if that janitor comes back up here, shoot him!"
We LoTo'ed the breaker and went on with our conversion.
NIH got a contract with a real Md licensed contractor after that.
