[thebluehawk]

A good example are the helicopters with workers inside that work on high voltage lines while they are charged.

The workers touch the lines to bring themselves (and the whole helicopter) to the same voltage and then get to work. That high of voltage should be fatal, but voltage is relative. They are at the same voltage and there's no path for the electricity to follow.

In a truly ungrounded system, if you touch one of the wires in the system, your body will match the voltage of that wire and nothing "bad" will happen. Only if that voltage has a connection back to the other side of the system will current flow through you, either by touching the other wire or if one of the wires is grounded and you touch the "hot" side.

[nkurz]

It's a great example, but a very different one. In the case of the helicopter, there truly is no path to ground. In the case of a person standing barefoot on wet ground, they (potentially) become the ground. If the human touching the wires is ungrounded (as in the case of the helicopter), there is no difference in this case whether or not the system itself is ground connected. The question is how much difference it makes for the system to be grounded if the human is also acting as a ground.