A properly designed and installed lightning protection mitigation system is the best defense against damage.
Though unpredictable, lightning is a very common event around the world. There are more than 40,000 storms every day producing more than eight million lightning strokes. These strokes can result in fires, damage to buildings, and breakdowns to electrical, telephone and computer installations. Damage results from electromagnetic fields from the lightning stroke, voltage differentials in ground systems, and structural damage from ohmic heating or mechanical forces. Damage can be attributed to insufficient direct-strike protection, inappropriate grounding and bonding that permit lightning currents to flow near susceptible electronics, and deficient Transient Voltage Surge Suppression (TVSS) protection.
What can be done to protect personnel and capital investments? The best approach to prevention is a properly designed and installed lightning protection (LP) mitigation system (Reference NFPA 780, UL 96 and UL 96A for LP equipment and proper installation procedures). The foundation upon which the LP system is built is a properly designed grounding electrode system, complemented with proper bonding practices, to create an equipotential plane and the application of TVSS to all power, communication and data signal lines.
The properties of a lightning stroke are indeed impressive, with an instantaneous power of over one megawatt and, on average, a peak current level of 30,000 amperes. There are three main lightning interactions that need to be considered:
1. Direct lightning stroke to the facility
2. Near stroke that induces large voltage impulses in metal conductors
3. Ringing results that occur when a tuned cable captures similar frequencies from the radiated stroke.