> One interesting point in all these circuits (that I have seen) is that
> they always seem to drive from the neutral. In Australia, we use a MENS
> system - where the neutral or "cold" of the AC line is actually tied to
> Ground at the point of supply entry into a building.

Almost the same here in the US, at least for individual houses.  There is
a transformer near your house that is fed from one of the three power
phases.  The secondary is center tapped with each half creating 110V AC.
The center is grounded usually right where the power enters the house.  In
my case there is a large copper rod driven into the ground right by the
breaker box.  Half the circuits in the house are between one end and the
center tap (neutral) and the other half between the other end and the
center tap.  Special 220V circuits like for dryers and electric ranges are
accross both ends of the transformer secondary.  Three wires are run for
each 110V outlet, hot, neutral, and ground.  The neutral and ground are
eventually connected back to the ground point, but the return currents are
all intended for the neutral and ground is for safety.  "Ground fault"
circuit breakers check for current in the ground line and trip if more
than a few mA are found.


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