"Paul Burridge" wrote in message
news
Hi all,

Anyone got any high-current/low-voltage horror stories they'd care to
share? You know; where your messin' about with a car battery or
something like that and forget to take your watch off or whatever.

Paul; I guess mine concerns 'zero amps'. Particularly, a motor generator
unit comprising a 48 volt 200 amp DC generator driven by a shaft coupled 3
phase 230 volt motor, which we moved a few miles. After supervising the
move, at night, I left the in charge technician and the crew to finish off
and went home to bed. Around 01.30h, I was roused by a phone call, "No
output". This unit HAD to be working by 09.30h at latest, next morning!
During the move the DC generator must have lost its 'residual magnetism' and
when restarted was putting out +9 volts instead of -48 volts and
consistently tripping the output circuit breaker when they tried to connect
it to the working equipment and batteries!
Although I had never encountered it before I had sufficient technical
background to surmise what had happened and after blowing a few fuses and
burning off a temporary lead in my hand was able to get sufficient negative
48 volt voltage onto the field winding of the unit. It recovered and was
there until all the equipment in that building was retired some 15-20 years
later.
Phew!
PS. 200 amps @ 48 volts is some 10 kilowatts, the output of one motor
generator set and there were 3 of them.