EN 62305
Part 1, General Principles, is an introduction
Part 2 defines risk-assessment-based level of lightning protection
Part 3 describes damage caused to life and structures
Part 4 addresses electrical and electronic systems within structures.
Confusion between primary lightning and surge protection devices
One misconception that needs to be urgently dispelled is the widespread confusion between lightning rods and surge arresters. People think they the same thing. Consequently, they believe that lightning rods protect buildings and their occupants. They don’t. At least not fully and not on their own.
A lightning rod is a primary lighting protection device – along with overhead earth wires and Faraday cages. It is a metal rod perched on the roof of a building that provides a low-resistance path to earth. It is connected to a down-conductor which runs electric currents down to a nearby conductive grid buried in the ground.
Primary protection, however, means partial protection. The lightning rod’s conductive grid is connected to the master busbar in the switchboard, so lightning current flows from the ground into a building’s power distribution system.
Nor do lightning rods protect against surges arising from the induction effect of lightning’s electromagnetic field or from strikes to overhead lines or into the ground nearby.
That is where surge arresters (also known as surge protection devices [SPDs]) come in.