As a young journeyman I hooked a 480 to 120 volt transformer up backwards (trying to get coil voltage for a starter to pull in an industrial saw). Turned on the breaker and heard a loud humming sound from the Xformer for about3-4 seconds and then BLAM, sounded like someone touched off a hunting rifle. The nearly 2000 volts we created was too much for the xforemer to handle even just sitting there, glad we didn't push the START button, would have blown the starter off the face of the earth.
A smokey, smelly valuable(expensive that is) lesson!
