Here's another one for ya:
Assume gas pipes are bonded to electrical ground at service entrance, in compliance with code.
Assume cast iron drain pipes to fixtures (hey, it's an old house!)
Since this is a grid-backup system, I naturally want normal use of appliances during power failures.
Scenario #1: I have a gas stove with some electrical stuff (timer, ignitor), so I plug it into "load panel"
Scenario #2: Well water fills a plastic holding tank. Booster pump supplies water to fixtures through copper pipe. I wire booster to "load panel"
Note that disconnecting ground between GroWatt and Utility Entrance solved the problem Ian showed in his video, that autotransformer sees voltage imbalance due to imbalance in the grid and tries to correct it, resulting in massive current flow.
With no ground wire, the two ground rods might be 12V part (voltage tolerance of transformer depending on load.)
Assume earth is fairly dry, negligible current flow and earthworms are relaxed.
In Scenario #1, gas stove is hooked up by a flexible brass or aluminum line to gas connection in kitchen.
This completes the circuit from autotransformer neutral to GroWatt ground to stove chassis, through flexible gas pipe, back to utility entrance ground, to neutral. The massive current Ian had seen returns. Flowing through flexi gas pipe. Life becomes interesting.
In Scenario #2, consider no gas line completing the circuit. Ground of circuits powered by GroWatt sit at 12V. Ground rod pulls nearby dirt to same voltage, but at utility entrance earth is at zero volts. You fill your tub, settle in for a nice warm bath (well grounded to earth by waste pipe.) You decide to add some more water, so you reach up and grab the hot water faucet with a soaking wet hand. (Above 30 mA, you can't let go. 12V/30mA = 400 ohms. What is the body's resistance with wet skin?)