That is a lot of corona rings, what kind of voltage for these breakers? The electrical systems I worked on were mainly 440, 240, 120 and 24 and I mostly never worked on anything that had those voltages hooked up, the only thing I had to stay away from was when a high pot test was being done on the things we put together to make sure no insulators had been compromised. While typing this post I just remembered seeing a gallon can of PCB oil setting on the factory floor next to a wall, PCB oil was highly di-electric, wouldn't allow high voltage arcing and was commonly used in transformers and high voltage switches, now days mineral oil is commonly used in transformers, like the stepdown transformers that are on the power poles that supply power to your homes. Over my years of radio and electronics hobby, I have probably had contact with PCB, don't know that it has ever effected my body as presently at 78 years of age, I feel pretty dang good, thank God.