My home has 3-wire single-phase supplied from the power company (Massachusetts, US). Red and black are separated by 180°. Both are 120 V from neutral (white). And in my electrical panel, neutral (white) and ground (uninsulated) are tied to each other and to a copper clad ground spike out in the yard.
Presumably the bare ground wires within the house never carry current except in the event of a short; but it goes back to neutral in the box.
Any 120 V circuit (a light bulb) is wired with one or the other of the two "hot" legs and the neutral; so presumably the original amperage supplied to the light bulb (minus energy dissipated as heat and light) passes thru the neutral line and then to ground. How much current does one actually see on the neutral line from the light bulb to the panel? How much current does one see from the panel ("behind" the ground spike, if you will) back to the electrical company transformer?
Any 220 V circuit (a clothes drier) is wired with both of the two "hot" legs and the neutral. In this case I would expect all current to see-saw between the two hot legs (minus the load again). Is there any current on neutral? Does the energy dissipated by the load appear as current on the neutral? Does any current appear on the neutral between the panel and the transformer?