Pauluk, yes the GFCI provides the needed safety. We can't use that on the service cable here due to the water-pipe alternative for neutral. The GFCI would trip constantly.
Lyledunn, yes, the ground rods of the system as a whole keep the voltage at a more or less constant relation to earth, but this does not rely on any particular rod; the rod at the building would not be needed as the others are doing their job.
Of course, neutral is ony at ground potential when no current is flowing, but since 30% or more of primary neutral flows back to the substation by way of the earth, there is always a small neutral/earth potential, sometimes negative.
Did I muddy those waters? If so, set table on fire.
Karl
