Was that on just now?
Years ago, a colleague and I were fitting some cables for some experimental kit on board one of the UK Royal Navy's finest. The cables contained something like 25 twisted pairs, all individually screened and armoured too for durability. The multi pole connectors were works of industrial art in themselves. All we had to do was run the cables from A to B and plug them in. They were the sort of cables that went where they wanted to rather than where you wanted, you had to work with them not against them.
After much effort we finally got the plug in the right place at the right angle to meet the socket on the big cabinet of important stuff that was on and running. We were assured by our host that that it was fine to connect them whilst the kit was on, and also it was really inconvenient to turn it off anyway because of all the downstream issues that would create.
The main power switch to the cabinet was at the top, on the front, right next to where our cables came out and right next to the socket we were aiming for. The only protection on the very unassuming toggle switch was a small guard either side and a note saying "do not turn off". At this point, my colleague says "was that on just now? Err, I think I better go and get Bob (our host)". I spent a few minutes in mild panic thinking "we're in trouble here" before Bob comes back, looks at the switch and says "yeah that should be on". He flicks it on and calmly walks off leaving us very relieved and breathing easier.
The rest of the fit went well and the kit did great service for a while until an unfortunate incident outside of our control meant that the kit was no more. But that's the deal sometimes.