Direct lightening strikes account for a very small portion of reported damage to systems. The major portion of damage is attributed to inductive coupling and ground potential differences.

This occurs when the line forms part of the induction loop. The line on one side and the power on the other side cause this.

Surge currents produce a magnetic field, which induces a voltage loop. The greater the rate of surge, the higher the voltage.

Equalisation occurs through the equipment of both sides.

The equipment is subject to different voltages when 2 installations in separate buildings are connected via a copper cable.

These differences exist when currents are flowing in the earth from adjacent strikes.

Equalisation occurs via the cables which in turn causes the damage to the equipment.