How could live and neutral wires be specified in a circuit with alternating current? I know that direct current has specific live and neutral wires because the current flow has a specific direction. But alternating current has no specific direction to flow, it changes the direction of flow after a specific time. So, how can the live and the neutral wires could be specified? Shouldn't it change when current changes its direction?
 A: Per the US NEC the neutral conductor is more properly called the "identified" or grounded supply conductor in branch circuit wiring. The grounded supply conductor of a branch circuit generally has white insulation, which is how it can be "identified" as the grounded or neutral conductor. It is bonded to the equipment grounding (safety ground) conductors back in the service panel.  The equipment grounding conductors in the branch circuit wiring  are  uninsulated (bare).
Hope this  helps.
A: In DC circuits, you’ll often find labels like +12 and ground. 
The battery providing that 12 volts just has two terminals: it doesn’t intrinsically know about “ground”. That “ground” label is a convention for the low-voltage common. We could connect another battery the opposite way to have ground and -12. 
The same is true for standard AC power outlets: one wire is hot at 120v, and the other is connected to ground and called neutral. 
(In most of the US, the National Electrical Code governs this.)
Why separate ground and neutral wires? That’s a separate question, but basically it’s a safety measure to prevent dangerous conditions if there are problems in the wiring. 
