I understand your points HSV, but there are numerous design decisions i made in this usage case. I tested the relays and made sure that if one contact was welded shut, it would be impossible for the relay to physically move and close the other contact with the other supply. This was my number one concern to be honest. The active/neutral are switched together, or not at all if the contacts weld. I wanted to make sure that the load would at no time be "Straddling" the mains, especially if one side was at high side of the waveform, and the other side was at the low side, effectively putting 480 volts across the load. No current would flow as such as the solar side doesn't have a MEN link, but it would still be dangerous to touch. The other issue is that i would never want the solar and mains to touch, but the exclusive break before make of the relays makes that impossible. However... i have decided that the next version of this being inside a much bigger box would use 3 sets of relays per "output", with a 10ms activation delay between them all, with AC detection as well. I'm not interrupting the earth, its using two 20amp diodes back to back to provide .6 volts of dc isolation to provide some basic noise protection from the solar inverter to the house mains. It will also mean that an ELB/RCD on the solar side will function. Without joining earths, an ELB/RCD combo unit wont work on the solar side, and it also leaves any mains equipment on the output of this unit a functional earth to prevent electrocution should the active or neutral touch the chassis. Without joining earths, on solar power, faulty equipment wouldn't trigger any kind of protection. The back to back diodes and capacitors provide a "earth" level for the entire solar side of the system, while also providing noise isolation from traditionally noisy solar charger and pure sine wave inverter equipment. In retrospect, the X2 caps probably arent doing anything useful. The inductance of the pigtails have zero effect at 50hz, and at higher frequencies would actually help limit high frequency noise, especially from the inverter. I have left them there mainly because the AC connections inside the power sockets aren't fixed, and as leads are pushed in and removed they actually move around a little. Using pigtails gives the copper some give so that it doesn't work harden and break off. The next version of this would also have 10 amp slow blow fuses integrated into it, at the moment im using the 10 amp circuit breakers in power boards for high current protection, which is not ideal. There will also be an RCD module connected to the solar side for even additional protection. (mains already has RCD/ELB breakers) I will also be doing some extensive testing on the earth joining and testing with a portable RCD unit to make sure what im doing is safe. I think for the moment, keeping the earth across the entire system as one (noise isolated) net is better for safety. My thinking is that it would prevent the entire solar system floating above or below the house earth, and even with no fault present, the earth of a metal case connected to the solar system being different to the earth of the house and possibly causing a shock. The solar inverter and DC side of the bank is all connected together, and also earthed outside to a copper rod i bashed into the ground, but there is no direct connection between house earth and solar earth, which is to prevent the solar system from being dangerous in the event of a mains fault in the house. There are so many "things" to think of in this case. Do you directly join the earth of the solar system to the house earth? House earth is also neutral due to the MEN link, so that means the solar system is now connected to the grid through the virtual neutral. That means in the event of a neutral fault the entire solar system becomes live!