I'm sorry I didn't see this thread before because there is too much off-topic discussion that makes it confusing and some of the on-topic responses just aren't correct. I'll re-focus:
123kid said:
But my question is that, how one wire is neutral. As we say that in AC current, the terminals change the polarity. Its mean that some time A will be positive and some time B will be positive. So when A is positve current will flow through one wire and when B is positive then current will flow through the other wire.
None of that is correct.
The "neutral" wire is so-called because that's exactly what it is: neutral. It is connected to the ground and therefore its voltage with respect to the ground is always (supposed to be) just about zero. The "hot" or "live" wire has an oscillating voltage with respect to this constant neutral: sometimes positive, sometimes negative. It pulls and pushes the electrons through the circuit.
A properly functioning neutral should not electrocute you because it doesn't carry a voltage with respect to the ground: it is "after" the load regardless of the direction of current flow, so it requires nearly zero voltage to push/pull current through it (but for safety reasons, you still should not touch it).
But the circuit is still a single loop, regarless of which direction the current is flowing. The live wire is pulling or pushing the current through the circuit, but in all cases, the current is the same everywhere in the circuit (it has nowhere else to go).
[later post] I want to know that is there current flow in both hot (live) and neutral wire in our home? or is it in single wire?
if we check neutral wire with tester, it will not show current.
Hopefully my above addresses most of what is wrong with this (mainly that the current must always be the same everywhere in a circuit), but there is an additional possible source of confusion: What kind of tester? Most people don't ever check the current in their homes because it is difficult and the equipment is expensive. They only ever measure voltage. So if you measure the
voltage of the neutral with respect to ground, it will always be zero whereas (in the US) the hot is 120V. If you measure the current, it will always be the same in the neutral and hot wires.
So, some more specific issues:
buckleymanor said:
To revisit the OP is the actual meaning of AC Alternating Current. Which is what the current does on the label and is why neutral can be as live as the positive when the current alternates.
No! The hot/live wire is not "positive", it is
alternating between positive or negative. The netural wire is always zero, so it
cannot ever "be as live as the [hot]".
I ignored most of the multi-phase discussion because it isn't relevant, but just to point out the difference between single and multi-phase, it is the neutral wire itself: multi-phase power doesn't have one. For split-phase (when using both) or three phase, both/all three wires are hot.