What is a practical surge rating for service entrance protection?
This is a difficult question and depends on many aspects including – site exposure, regional isokeraunic levels and utility supply. A statistical study of lightning strike probability reveals that the average lightning discharge is between 30 and 40kA, while only 10% of lightning discharges exceed 100kA. Given that a strike to a transmission feeder is likely to share the total current received into a number of distribution paths, the reality of the surge current entering a facility can be very much less than that of the lightning strike which precipitate it.
