I have wondered about this for years and decided today to research further. In a mains AC installation neutral is tied to ground (here in Australian anyway). Everything I have read states that neutral provides a return path for current flow. I am confused as to what happens during the negative half of the AC sine wave? How can the neutral line 'source' current? Does current flow from neutral to active during this period? When current is generated in the power station how is the negative half of the sine wave generated?