I understand that in an ungrounded system, a single ground fault would not cause an overcurrent condition that would trip a breaker.
But overcurrent is not the only thing that a breaker can be designed to detect. If a breaker were designed to detect and trip on a ground fault in an ungrounded system, then IMHO this would serve the purpose of ground fault detection.
I can think of several plausible ways to implement such breakers, though I don't know the precise details nor if anyone sells systems that would do this.
For example, something like a GFCI type breaker would detect the capacitive charging current flowing through the ground fault. A system using coordinated ground fault detecting breakers might be sufficient to detect and _trip_ on ground faults. Such a ground fault system would function with an impedance grounded electrical system, I don't know if it would function properly with an ungrounded system.
-Jon
