GFCI works correctly either way. Their operating mode doesn't care at all about ground: Whether bonded, not bonded, or not even present (look, ma! only two wir

GFCI works correctly either way. Their operating mode doesn't care at all about ground: Whether bonded, not bonded, or not even present (look, ma! only two wires!), they still perform the same way. They respond to an imbalance in current flow betwixt line and neutral. What goes out must return; if it doesn't, then switch off. Ground is not part of the equation at all.