The only function of the shore power ground wire when you have an
isolation transformer is to return short circuit current back to the
source so it will blow the dock circuit breaker. Although the
probability of an electrical breakdown on a transformer is minimal, the
metal frame and the copper shield should be connected to the shore
power ground to provide this return circuit. The transformer frame
should not be connected to anything on the boat and it should be
mounted on an insulated support in a metal boat.

When purchasing an isolation transformer, getting one with adjustable
voltage taps on the input is worth the extra expense if you are
traveling to foreign ports. Our transformer can accept input from
about 80 volts to about 450 volts with different tap settings and in
addition to foreign adaptability, it has helped out on docks suffering
from low voltage.


wrote:
I have one with the earths in accordance with the sterling power
diagram. It was not very expensive - £175 for a 3.6kVA. When I was
installing the shore power its use was instantly demonstrated whilst
still on dry land in the builders shed. The building's neutral was
showing +12 compared to earth, once onboard after the ship side neutral
had been bonded to earth, the ship side neutral was of course at Ov.
The other major advantage of an IT is that you no longer have to worry
whether the shore supply itself is wired correctly - Live is Neutral
and vice versa.