A spectral study of lightning's typical impulse reveals both a high and a low frequency content. The grounding system appears to the lightning impulse as a transmission line where wave propagation theory applies. Earth loops and differential rise times must be avoided. The grounding system should be designed to reduce ac impedance and dc resistance. The shape and dimension of the earth termination system is more important a specific value of the earth electrode.
Ground rings around structures are useful.
They should be connected to the facility ground. Cathodic reactance should be considered during the site analysis phase. Regular physical inspections and testing should be a part of an established preventive maintenance program. Ordinary fuses and circuit breakers are not capable of dealing with lightning-induced transients. Lightning protection equipment may shunt current, block energy from traveling down the wire, filter certain frequencies, clamp voltage levels, or perform a combination of these tasks.