Please confirm that there is no connection between the ground rod attached to the Barn Main PNL and ground rod at the Barn Aux. PNL.Mike Curran wrote: ↑Thu Apr 02, 2020 9:35 am There are 2 subpanels in the barn, not counting another separate subpanel for the 2012 grid-tied array which isn't shown on the schematic. The one called "BARN MAIN PNL", is grid-supplied only and supports normal lighting, outlets, a mini-split heat pump (which I may move over into the backup panel at some point) and overhead door. This is the one whose ground (#10 wire) is connected to the Main Distribution Panel. The other, called "BARN AUX PNL", is normally supplied from the Skybox load output (can be switched to grid via bypass breaker in that panel), and supports two (or 3 when thermostat calls for it) hydronic heating system circ pumps (~150 watts each) and a small fridge that only runs around 40 watts. The #10 ground connection you see is still within the grid-exclusive system. Sorry that wasn't clear in the schematic.
Are we having fun yet?
Engineers consider solving problems as fun, especially when they are someone else's problem. I will be doing some more reading on separately derived systems, the next couple of days.
I also have not used an O-scope for years. There are some interesting, low cost units available now that connect to a PC by USB. Would be more than adequate for this application and something that I have considered purchasing.