I can tell you that, since reading this thread, I grip my Grinder like my life depends on it.
Sometimes thats not enough. Many years ago I got a service call to a used car lot. He had a small body shop in the back.
The compressor on the unit I was working on had tripped out. As I was wondering what was going on, the overload clicked back on and the condenser fan came on.
It sounded like a jet engine winding up. Then the overload tripped. About that time, I heard all H*ll breaking loose out in the body shop. Slamming, yelling, sounded like a fight.
I was looking that way, when the owner came out of the little building I was next to.
He said he did not know what the heck was going on, but when he came in to work a few minutes ago, the clock, radio, water cooler, overhead light, every electrical gadget in the office was not working.
Then I saw two guys coming out of the body shop. One was sorta helping the other, who was holding his arms out strangely.
He said he was going to take him to the hospital, he thought one of his wrists was broken, and the other one might be.
The hurt guy was looking stunned. He said that he had picked up the big 10 inch grinder, turned it on, and it attacked him. Twisted its self right out of his hands injuring both wrists as it did.
Then it ran around the shop for a few seconds slamming into his ankle.
Something clicked in my mind. I grabbed my meter, and checked the voltage on my machine.
It was supposed to have 120 volts out of the wall socket. It had 240!
I pulled the cover off the breaker panel in the office, and there was 480 volts on the 240 line coming into the building.
I pulled the main, and we called the power company.
Turned out, the transformer on the pole had blown during the night, and the power company had replaced it.
But they hooked up the wrong tap on the new one, and put 480 volts on the 240 line.
When the body shop guy turned on that big grinder, the torque of the overvoltage motor twisted it right out of his hands.
I don't know what the car lot guy got, but they bought my company a whole new machine.