Large masses spinning at high speed are terrifying!
I would be a bit nervous firing up a GIANT pedestal grinder that we had at the college where I was taking manufacturing classes. Someone told me a story about it sending a wheel through a wall once. I always stood off to the side of that thing. The sound it made starting up was sweeeet though.
That STL-10... that is interesting. As if someone didn't size the OCPD to the wire. I can't say exactly what happened, but that wire had to be passing some ridiculous current to do that, depending on how long the siren was activated before the video started. Certainly it was long enough that even something with a generous trip curve (as you would use for a motor) should have cut it off.
Always size the protection device to the wire... I have SEMI S22 Table A1-1 committed to memory at this point
. For those wondering, S22 is the electrical code specific to the semiconductor industry, largely derived from NFPA79.