Is it O.K. to bring a 3/0 ground wire into a transformer through a 3/4" hole on the side of the Tx with a plastic bushing (no connector). It is not in a cable...just a 3/0 wire alone?

Sure you can but if there is a chance of someone getting snagged on the ground wire and pulling on it I would use a connector just to keep it secure.

RobbieD I believe you are refering to rule 12-3024(1)(b).

The ground wire must have a connector and I would suggest a metal one to ensure good electrical connection to the case. In a High fault or lightning strike it is possible that the loose wire could move also the possibility exists that the bushing would make the case a choke and oppose the flow of current.