A transmission ground wire hangs above power and data transmission cables, acting as a static shield. These shields are so important that most electrical transmission systems use two overhead ground wires instead of just one. The wires have a steel core, which is ideal because they only carry energy when struck by lightning.
When lightning strikes, it hits the overhead ground wire rather than the transmission cables below. The energy travels along the steel core of the shield and moves down the wire. Like transmission lines, the ground wire runs between utility poles and support towers. At each structure, the wire safely discharges the energy into the ground, preventing damage to the power lines.
Without a static shield, lightning strikes can cause a surge of energy in the transmission cables, potentially leading to flashovers between support towers.
