I had a job to replace 6-strings of batteries in a 10,00 amp telephone power plant. We had finished 5 strings over a period of six weeks, and we had the last string ready to go on charge at 6 AM on the last day. Everyone was a little bleary eyed after working all night, and it was my task to connect this last string to the 800 amp MG set we used for a charger. I connected the 4/0 charge leads, started the unit, and began cutting out the field resistance. Just before the reverse current relay operated to close the charge contactor, I glanced up at the voltmeter - it was headed the WRONG WAY! TOO LATE! The contractor slammed closed, fire shot out of the arc chute and bounced off the ceiling, there was a terrible noise as the generator tried to reverse the 75-hp drive motor, and then, mercifully, the motor controller over-current trip did it's thing.

Hooked 'er up backwards...

I always did a polarity check after that!

Hank


...from the Gadget Garage