Is Your Charger Switch Properly Wired?

On a boat we were on recently,  there was a battery switch near the house battery bank. The battery bank, inverter, and house feed wire were all going to the battery switch. It took a while to figure out what was going on until we pulled it off the wall and looked where the wires were leading. Turning the switch off did not kill the house loads, nor did it kill the inverter / charger, which kept humming when the switch was off. So what was it doing? It was disconnecting the house battery bank but keeping the inverter / charger connected to the house loads. As a result, the charger was directly powering the house loads when the switch was off. This is really bad for the charger! Can you guess why we were called in? The charger was intermittently working.

In this setup, when the switch is off the house loads are still being powered, the batteries are not being charged, and the charger is being damaged. This is pretty much the worst way the switch could be wired. The charger should always be on the battery side of the house switch, so that when you turn off the house switch, everything on the boat shuts down but the batteries still charge. Because this is an inverter / charger, it also needs its own switch. So now the boat has two battery switches at the house bank: one to shut the house loads off and on, and the other to disconnect the inverter / charger. This one is only used for service or emergencies.