The most popular methods of lightning protection have involved the use of passive Franklin air terminals, horizontal and vertical conductors or combinations thereof. The LP system is dependent on the ground electrode system to effectively dissipate lightning energy into the earth. The characteristics of a ground system under the impulse conditions of a lightning stroke are important if an effective LP ground system is to be implemented. This ensures that the grounding system provides low ground impedance and not just a low resistance. This is a central point to the philosophy of LP ground system design.
The injection point on the structure can reach hundreds of thousands or even millions of volts relative to remote earth, due to the lightning stroke. The dominant factor attributed to this large impressed voltage is the product of the inductance and the rapid rate of current from the impulse. It is this type of large voltage rise that leads to the hazard known as flashover — arcing from the LP system to an adjacent metallic conductor due to the dielectric breakdown of air between the conductors. Therefore, a low impedance ground is essential to the performance of the LP system.