J. C. Mc Laughlin wrote:
Dear Jeff: Many thanks.

It is especially interesting to learn that the expectation of encountering a
floating (no earthing) system is zero.

Expanding a bit on what you have communicated:
It appears that the transformer used between one phase of a HV 3 phase line
and distribution "wires" is 440VAC, center tapped. The distribution "wires"
to a house (or the like) are one side of the aforementioned transformer's
secondary and the transformer's center tap, which is labeled as neutral. It
is expected that another house (or the like) is fed from the other side of
the transformer's secondary and its center tap.

This is not what a 3-phase system is. What you describe is a 2-phase system.

A 3-phase system has 3 live wires, a neutral, and possibly a ground.
The 3 phases are 120 degrees apart, not 180.
Each phase has a voltage (230V here), and there is sqrt-3 times that
voltage between the phase wires (400V here). All three phases are
used in some electrical motors and in highpower applications like
electrical heating, and one of the phases is sufficient for a normal
house connection.

At the service entrance: one scheme connects the neutral to an earthing.
An alternative (called 'protective multiple earthing' (PME) ) does not
connect the neutral to an earthing, but connects exposed metal in the house
to an earthing. Wow! The latter scheme is expected in new construction.

Why "Wow!" ?
It is the only safe system.

Here in the Netherlands we have the same situation. Power is distributed
over 4 wires (3 live phases plus neutral) and a 5th wire is locally
distributed for safety ground. It is connected to the safety ground
connections of all reeceptacles and to metal structures in the house,
like water and central heating pipes. The neutral is only connected
to ground at the substation, and usually has a couple of volts on it
when measured at the receptacles.