Originally Posted by Hein
Thank you for clarifying. If there is current on the ground then would that not reduce the current on the neutral and cause an imbalance that then causes the GFCI to trip?
If your inverter remains powered up, or it's disconnection method affects only the "hot" 120V interconnect, then your Inverter allows the 120V shore-powered appliances to "leak" current into the 12V
In Airstream, the 12V
system is negative grounded: The frame, the battery terminals, and many "white wires" are all interconnected. But, when the 120V power cord is connected to shore power, this bus (i.e., the frame and aluminum skin) are connected to the power cord GREEN safety wire.
At the Inverter, even if the 12V
"hot lead" (and/or 120V "hot" output leads) are disconnected, the safety "green" and current carrying neutral "white" leads for 120V service are apparently still interconnected with that 12V grounding bus. (The potential of the 120V "grounded" connection floats a bit, via high capacitance - but it's not going to differ by much.)
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Your problem is: An 120V appliance, powered by shore power through a GFCI, can leak return current back through the GREEN wire on the Airstream power cord. The return current path is: appliance cord -> socket -> white wire -> Current carrying Neutral Bus. At this point, some current goes out (correctly) through the white wire of the poser cord. But at least some current also goes through white wire(s) into the Inverter.
The Inverter behaves as a power panel without an explicit grounding lug. The current-carrying "white" return current leaks to the frame ground, and it then gets routed out through the power Cord GREEN safety wire.
The GFCI at the facility sees unmatched current (returning "neutral current too small), and trips up. You need to disconnect both
the 120V Inverter "hot" and Inverter "current carrying neutral return" leads (or busses) from the 120V system when shore power is present.