Aj_777

Hi, it seems that you are mixing terminology by referring to the output as a positive terminal and neutral terminal. It can be assumed you mean Live and Neutral output terminals. It's hard to tell as it depends on the connection after the output, to the essentials DB, and what is going in in there. Perhaps Earth is connected to the Neutral bar, or similar, and the load is sourcing the Neutral that way. Seems like when you switch off the Mains, that circuit is broken and no longer provides a Neutral path. In any case the output is a separate supply point and the Live and Neutral connections need to be used for loads. Check what your inverter specifies for the Neutral connection, whether the changeover is internal, or you need an external relay to switch it to the load. If something was blowing up then you have serious issues downstream at the essential DB end. Best to get a qualified Electrician to check the recommended circuit connection against how it is currently wired, as it seems that the basics are not in place

Does it display any error codes? I'm assuming that you don't have BMS comms between the battery and the inverter, and setting float voltages manually.