why should neutral wire carry the current back to the source

Question

anonymous · Answer

To complete the circuit. However, with AC there does not have to be a circuit because the current can be stored in and returned from a capacitor. Do you need to know more about capacitors?

shane_b · Answer

The neutral wire is needed because without it, there is no potential difference across the load and therefore, no current will flow.

Regarding capacitors, they don't store current...they store energy in an electric field.  Even with a capacitor, there still needs to be a potential difference for it to discharge...hence, there must be a circuit.

anonymous · Answer

Sorry Khanitha, Shane B is right; capacitors do not store current because current is dynamic, I used the term as a short hand and yes, there does need to be an earth or return connection on the other plate of the capacitor but there is a physical discontinuity across the plates of a capacitor and a DC current would not flow.. And for current to flow there has to be a potential difference across the load and this is provided by the return (or Neutral) cable. So perhaps my answer was inadequate; for which I apologise; I hope to get better at this.

radar · Answer

Since you used the term "neutral" I am assuming you are talking about commercial electric as applied to residences.  Here in the U.S.A. where household receive 240 VAC AND 120 VAC, in many of the 240 VAC loads like dryers stoves etc.  the neutral carries minimum current (accomplished by balancing the loads.  The 120 VAC the neutral current will be similar to the other wire (hot wire).

radar · Answer

|dw:1341974948802:dw|  Only a halfcycle is depecited, the other half of the cycle all current changes direction.  Note that if the 120 loads are equal, the neutral wire would theoritcally be zero.  It is still necessary as the 120 VAC loads vary and the neutral must carry the difference.