7.1 Preventing galvanic corrosion The answer to prevention is quite simple. To prevent corrosion the electric circuit must be broken. Although this is nearly impossible to achieve with the small circuits between the different metals attached to the boat, it is achievable with the shore power connection. The easiest way to break this circuit is to not connect the shore earth to the hull. However, this is unsafe and not recommended, because this results in the hull being not sufficiently earthed and therefore a satisfactory working of the RCD cannot be guaranteed anymore, leading to unsafe situations on board. There are safe ways to prevent galvanic corrosion without compromising safety. This can be achieved by using a galvanic isolator or by using an isolation transformer. 7.2 The galvanic isolator The galvanic isolator consists of two diodes connected in anti-parallel. The galvanic isolator is connected between the shore earth connection and the central earth point in the boat. The diodes in this configuration conduct electricity in both directions only when a certain threshold voltage is reached. The threshold voltage is approximately 1.4 VDC. The threshold voltage is higher than the galvanic potential difference between the various metals. In this way no galvanic current can run. On the other hand, a higher earth fault voltage in the AC circuit will be allowed to pass through enabling the full functioning of a connected RCD. The advantage of the galvanic isolator is its low weight and size, the disadvantage is that this unit relies on a good earth conductor. Another consideration is that galvanic corrosion can also take place through the neutral conductor, this in cases where the neutral conductor has been connected to earth trough one of the electrical appliances on board, like a suppression filter or other appliances.
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