Powersafe have developed an Earth Safety Device which monitors the voltage on the earth path and will isolate power if there is a fault. It can be used on a mains connected supply and also on invertor generators, UPS and invertors. The video here gives examples of the kind of faults the Duo can protect against.
How to test the Duo
This video demonstrated an RCD DUO being tested and shows the current and voltage required to trip the unit, thus isolating the power supply.
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