Quoted from BigAl56:With the Isolation there is no physical path to ground and it minimizes the electrocution hazard of having 110v AC on the backbox.
Bingo...that is why operating rooms use isolation transformers for all the power in the room. No way to ground the patient. Go back 50-60 years ago, it was a different (unsafe) story. And no, Ralph Nader didn't figure this out.