FWIW, For car use, an inverter is considered to be 'Above Earth' & as such, there is no 'return path' for the current to follow. They can be earthed, 'along with ALL your appliances', but I would not advise this, as this introduces the return path. Just don't get across the 240 volt, Active & Neutral. As Phil has stated, consider it LETHAL.
L.