Byron;

C-H answered the question very concisely!
Good job, C-H!!! [Linked Image]

AC current flows in both directions in the circuit - regardless if the circuit is Line-To-Line or Line-To-Common (AKA "Neutral").

Current flows in one direction for ½ the cycle, then flows in the opposite direction for the last ½ of the cycle.
This happens whether or not the circuit has a Grounded Conductor. Grounding a circuit Conductor only drives it + the System to a "Ground Reference" - it doesn't create a Half-Wave situation between an Ungrounded Conductor and the Grounded Conductor.
(BTW: "Neutrals" are commonly Grounded Conductors)

Let us know if you have additional questions regarding this topic! Feel free to ask away!

Scott35

p.s. the DC 3 wire system C-H is referring to can be found in the Technical Reference section.
Also, under normal situations, there will be almost no current flowing in the Earth ground its self.

Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!