Technical article from Blue Sea Systems
In the US inverter/charger installations that are used in marine applications must have ground-to-neutral switching. The purpose of this is to guarantee that the neutral and the green wire are common after the green wire connection to neutral that is achieved through the shore power cord exists after the cord is disconnected or shore AC is no longer serving as the boat's AC source. There must also be only a single ground point in the AC system. This prevents a voltage differential from developing between the boat's AC neutral and the shore or genset AC neutral, which may cause an electric shock or nuisance tripping of GFI's.
With an inverter/charger operating in the inverter mode the AC output neutral should be connected to the boat's green wire safety ground system. In battery charger mode the inverter/charger output neutral must be disconnected from the AC safety green wire, so that the single point neutral-to-ground connection is made by the external AC source (shore or genset).
Neutral to Ground switching is not done in Canada.
Original article from Blue Sea Systems