The importance of ensuring that the system provides a low earth impedance, and not simply a low
earth resistance, must be understood. A spectral study of the typical waveform associated with
transient impulses such as those characteristic of lightning and switching surges, reveals both high
frequency and low frequency components. The high frequency is associated with the extremely fast
rising "front" of the transient while the lower frequency component resides in the long “tail” of the
decaying impulse.