6.3 Inverter/charger combinations When combination inverter/charger units are used, the neutral to earth connection are different. Depending on the operation mode of the inverter/charger, shore power is being used or independent power is being generated. While connected to shore power a connection between ship earth and shore earth will need to be made. While the inverter/charger is inverting and acting as a power supply, it will have to make an independent earth connection. As it is sometimes not clear which of the leads in the shore power cable is connected to earth, a short circuit to earth can be created. Depending on the country, a mains connection can sometimes be made in two different ways. It is also possible that phase and neutral have not been wired correctly in the plug or in the shore installation. Inverter/chargers contain an internal ground relay; this relay automatically makes or breaks the connection between the earth and one of its outgoing phases. In case of an incoming voltage firstly the connection between the earth and the outgoing phase will be broken. Secondly the incoming voltage will be coupled to the boat network, after having been synchronized to accommodate a seamless transfer. Please see below for both situations. Situation 1 The boat is connected to shore power, the AC input relay is closed, and the neutral-earth relay is open. The AC output system relies on the shore connection to provide the neutral to earth link, so the RCD is functional
Situation 2 The boat is now disconnected from shore power, the AC input relay is open, and the neutral-earth relay is closed. The inverter/charger has made the Neutral to earth link itself, this so the RCD in the AC output circuit is operational.
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