The ground wire is above the phase lines because it serves to protect the phase lines from direct lightning strikes. The ground wire intercepts the lightning stroke and safely conducts it to the ground through the tower and the grounding system .The ground wire also reduces the voltage rise at the top of the tower due to lightning, which can cause flash-overs between the tower and the phase lines. The ground wire is usually made of steel, which has high mechanical strength and low electrical resistance.
Some ground wires also contain optical fibers for communication purposes.