Hi ScottyUK;
It provides almost the same level of protection as it does on a grounded circuit. There is always almost enough capacitive current in a system of any size to give you any thing from a good tingle to serious injury, depending on the size of the system, the capacitance of the cables and the presence of any high resistance paths to ground.
This current is distributed throughout all the wiring in the system.
If you contact a hot conductor and ground, only a small amount of the ground current will return through the circuit you have contacted. Most of the current will return to the other hot lines through the impedance to ground of the other circuits.
The Ground Fault breaker will see this unbalance and will trip if the current is higher than the breaker set point.
I said almost as good protection.
On a conventional grounded system, the breaker will not protect you from contact with two hot wires of different phases. However, if your body is grounded there is a chance that enough current will bypass to ground to operate the ground fault feature of the breaker. You can't count on this, it comes under the heading of "sometimes you get lucky".
You can get a serious shock to ground on an ungrounded system. A ground fault breaker will usually "SEE" most of this "shock" current, but you can't gaurantee it.
Re: grounding of ships systems;
consider this scenario;
A ship with an ungrounded system ties up and connects to shore power. For some reason their system is drawing a heavy neutral current. There is a long shore power cable back to the distribution center and the grounding grid of the shore system. In a large dockyard, the grounding may be an extensive grid. That is, a lot lower resistance to ground than if a few ground rods were driven. The proximity to the ocean also tends to favour good grounding conditions. The neutral current is causing a voltage drop on the neutral and neutral potential out on the dock is not at true ground potential.
This is no problem as the neutral is not grounded to the hull.
Now, another ship ties up alongside and goes on shore power.
They are tied onto the same cable as is feeding the other ship.
This second ship has a grounded neutral system. You have now connected the neutral to a very large ground electrode. The hull of the ship. In some cases most of the neutral current will flow through the hull, through the sea water and back to the ground grid. This may cause hull corrosion and will definitely shorten the life of the anti-corrosion "Zincs".
By the way, there will probqably be no corrosion issues with the ship whose unbalanced load and heavy neutral current is causing the corrosion.
yours
