Victron Galvanic Isolator VDI-64

The galvanic isolator prevents electrolytic corrosion. It blocks low voltage DC currents entering your boat via the shore power ground wire. These currents can cause corrosion on the boat's underwater metals such as the hull, propeller, shaft, etc.
The galvanic isolator consists of two diodes that are connected anti-parallel. When connected in this way, the diodes will pass current in both directions, but only above a certain threshold voltage. The voltage at which diodes conduct is around 1.4 Vdc.
The isolator is installed directly behind the 230V connection of your boat. The forward voltage of the galvanic isolator is higher than the potential difference between the metals. Therefore, this voltage does not allow conduction and the galvanic isolator thus prevents any electrolytic current. However, if there is a (higher) fault voltage in the AC circuit, the diodes allow a current to pass and the residual current circuit breaker breaks the circuit.