Dick I have a 110/229v -220/110 inverter that faults dead when there is a problem, I think this is isolation you mean, + all the plugs are gif ground fault sockets.

My recommendation is to use a transformer that isolates the circuit under test from the power line. The GFI is almost as good, I prefer using both -my house has earthed tile floors and I don't want to trust my life to only one safety mechanism.

 

A GFI saved me once.
But I can attest you still get a good jolt before the breaker trips.