Once you have checked, double checked, and triple checked all of your connections, you are now ready to wire your output to your socket. Sockets are labeled with live, neutral and.... earth?
We havent talked about earthing at all yet, so we will do that now.
It is essential to make sure that your output is always connected to earth, we are going to accomplish this by using an "earth loop". The alternative to doing this is switching your earth using the third pole of your relay. I belive this is wrong as all alaments of your circuity should be continuously earthed. We will use the earth pin from the UPS input plug to connect both the output earth and inverter earth to your household earth circuit.
Once again, this is explained in the diagram and video