The level of protection recommended for a site is dependent on environmental factors affecting the potential surge exposure. A full risk assessment of a site can be obtained by applying the IEC 62305 series of standards which includes a systematic approach for the application of structural and electrical protection. The following is a simplified analysis of the recommendations for electrical protection.
Lightning flash density provides a statistical measure of lightning flashes per square kilometre per year (Ng). Obviously the risk of lightning related damage increases in areas with a higher lightning flash density. Approximately 70% of all lightning occurs in tropical regions with a total of 1.4 billion flashes per year.
The location of the site and method of delivery of electrical services influences the risk of damage due to lightning activity. Selection of the appropriate surge protection device at the point of entry to the site will provide an effective solution for the given environmental risk. It is not economically feasible to implement a lightning protection system to cover 100% of all lightning events. A standard IEC 62305 risk assessment aims to reduce the risk of economic loss to one event every 1000 years
The following is a simplified risk assessment for point of entry protection based upon the most influential environmental factors. A more detailed analysis can be achieved through a full IEC 62305 risk assessment.