When properly installed, Charles Marine Isolation transformers will electrically isolate the AC shore power from the boat's AC power system. The boat's electrical system and the grounding conductor are not actually connected to the shore-side power. There is no direct electrical connection between earth-grounded shore AC power and the onboard electrical system. The shore ground is connected to a shield that is wound between the primary (shore) and the secondary (boat) transformer winding. The connection of this grounding wire only to the shield of the transformer isolates the boat's AC electrical system from shore.
Compliance with independent testing lab requirements maximize safety