Electronic – How to discern earth from neutral

There must be two wires for a complete circuit.

Now, in a balanced AC circuit, both wires provide an alternating voltage with respect to ground (earth). When one wire is positive, the other is negative.

However, in an unbalanced system, one wire is neutral, which should ideally be at 0V with respect to ground, and the other is hot which alternates positive and negative with respect to ground.

In either case, both wires have (ideally) equal and opposite current.

If I'm not mistaken, in the USA, the neutral and ground are connected together at the meter base (service entrance).

For a generator that isn't referenced to ground, the AC voltage is simply across the 'hot' and 'neutral'.

There are devices for converting unbalanced AC to balanced AC power.

Where is that quote from? It is self-contradictory, and pretty much just plain wrong.

Current will flow if a load is connected between a generic power supply positive and negative, no ground connection is needed, unless you have some special purpose power supply.

A ground connection is often used for safety, especially in line non-isolated supplies, or as a means to reduce noise. Even so, not all supplies pass the ground on to the output terminals or even make it available (for common examples, think wall-warts and such with just a two pole output). Many supplies don't even have an incoming ground terminal from the mains (small switchers, and again, wall-warts).

I was going to post this as a comment, but it seemed to cover the question.

Edit as per comment below and corrected text.

Well, that does change things. Generally, a DC power supply has no output tied to ground, or connected to the supply electrically at all, so connecting a load between an output and earth ground would result in no current flow. Supplies that have an output set of terminals and a separate ground can often be configured (by jumping ground to one of the output terminals) as positive ground or negative ground if desired.