A guard wire or earth wire is the topmost conductor in high-voltage transmission lines. It is used mainly to protect lines from lightning. If in case lightning struck, then it carries the excessive current inrush to ground.
Its radius is much smaller than the actual transmission wire because as the resistance is inversely proportional to area of cross section and as the cross section decreases, the resistance increases. The increased resistance of earth wire is able to withstand high inrush of current caused due to lightning and it will safely guide this inrush into ground.
It is called a guard wire or earth wire used mainly to protect lines from lightning. If in case lightning Strucks then it carries the excessive current inrush to ground. Its radius is much smaller than the actual transmission wire because as the resistance is inversely proportional to area of cross section and as the cross section decreases, the resistance increases. The increased resistance of earth wire is able to withstand high inrush of current caused due to lightning and it will safely guide this inrush into the ground.
It is placed above all the conductors mainly because if lightning Strucks then it will struck at the uppermost point in the line configuration and protect the actual conductors .