The galvanic isolator prevents electrolytic corrosion. It blocks the low-voltage direct current that reaches the ship through the shore power grounding conductor. Such current can cause corrosion in the ship's underwater metal components, such as the hull, propeller, shaft, and so on.
Inside the galvanic isolator there are two diodes connected in antiparallel to each other. When this type of connection is used, the diodes allow the electric current to flow in both directions, but only above a certain voltage threshold. The direct voltage that ensures the conduction of the diodes is approximately 1.4 V.
The isolator is installed directly behind the ship's 23 V connection. The forward voltage from the galvanic insulator is higher than the potential difference between the metals. As a result, this voltage does not allow current to flow, and therefore the galvanic insulator prevents electrolytic current. However, if a (higher) fault voltage is present in the AC circuit, the diodes allow the current to pass and the residual current device interrupts it.
