In the 3-wire 120/240 volt Edison style single phase wiring system as found in North American, a neutral can be shared between opposite phases, carrying only the current for the imbalance between the phases. In times long ago, there was no separate grounding wire; the neutral served as the ground. But the grounding wire was added, initially required only on some circuits (the laundry room was first).
Clearly there is some level of hazard in the neutral wire. But just how much? Clearly it is a big hazard if it becomes disconnected from its source, and the imbalance between the phases is now a voltage on that wire, energizing everything that is connected to it (as was the common case decades ago).
But what I'd really like to know is how safe is it in normal connections where it is properly connected, but may be run some distance from where it is bonded to ground, possibly via a subpanel where other circuits could contribute some voltage to it when running out of balance.
Q: Would you feel safe grabbing a neutral (presume you are absolutely positive it is not a hot wire) while standing in bare feet on a wet concrete slab?
Q: Would you feel safe sitting in a tub with the neutral wire either within reach, or dangling into the tub itself?
Here's where I'm going with this. Certain situations require ground fault circuit interruptor protection to prevent shock on a ground fault path. These are generally "wet" situations such as the electrical systems of a hot tub of jacuzzi. The idea is if something goes wrong and a path to the water is set up, a small leakage current will interrupt the circuit. But the issue is that in the case of 240 volt loads, GFCI is done via a 2-pole circuit breaker. The neutral runs through the breaker to be part of the leakage measurement, but it is not disconnected when the breaker is tripped off. There are such things as a "switched neutral" breaker for places where a neutral voltage is recognized as a danger, but these are not GFCI breakers.
So basically, this GFCI protection does not disconnect the neutral wire. I'm told that most GFCI receptacles for 120 volts do disconnect the neutral.
Where can one find a GFCI protection device that disconnects both hot phase wires and the neutral at the same time?