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Quoting "Edmiston, Mike" <edmiston@BLUFFTON.EDU>:...
...
Speaking specifically about the _distribution_ system i.e.
the ~17kV stuff that killed the local pool-maintenance guy,
the answer is simple: less cost, i.e. one wire instead of two.
...
The earth-return system is not just a cheap trick, it is a
dirty trick. In many locales, the conductivity of the dirt
is not large compared to the conductivity of underground
pipes.
> Today we can detect faults with GFCI devices.
> These work independently of whether the system is
> grounded or not by comparing the current in the
> two wires to the device, and breaking the circuit
> if the two currents are not equal-opposite.
Not quite. That would work with a two-wire system
(more precisely, a wire-return system, as opposed to
an earth-return system) whether or not one side of
the system was grounded.
A GFCI cannot possibly work with an earth-return system.