活線中輸出的交流電會否改變方向？

one point you have to clear:
Live wire : -220V to +220V
Neutral wire : 0V

Live wire is a continuosly sinusoidal wave with 50Hz and its alternating from 220V to -220V,

when the voltage of live wire is higher than the neutral wire,the current will flow from live to neutral(live:220V,neutral:0V)

when the voltage of neutral wire is higher than live wire,the current will flow from neutral to live(live:-220V,neutral 0V)

Although in some period,absolutely have current flow FROM NEUTRAL TO LIVE,but it not representing that the neutal have voltage,in that period,is the voltage of neutral is higher than live,but the neutral skill maintain in OV,sine neutral is connected to earth(earthed).

嚴格講交流電係正負極向交替變化，但你所謂方向改變只適用於某電路內的電流流向解釋意義，例如你定義電流從正到負或從負到正之方向係相對。普遍人認同電流由高電勢流向低電勢(可能電流與水流類同)，相對於中綫，無論火綫當時係正極或負極都係高電勢，所以交流電係改變電流方向嘅慨念並不確切。