Correct protection principles may be applied by introducing the international standards IEC 61024-1 (protection of building structures against lightning) and IEC 61312-1 (protection of information systems LEMP).
These standards define the correct procedures to be followed to install an effective lightning protection system. It is important that the protection system includes both structural and surge protection equipment.
According to the IEC 61312-1, the entire installation is divided into different lightning protection zones:
- LPZOA This zone is an area where a direct hit to the structure is possible. The current may rise to a value of 200,000 A (10/350 ms) producing extremely high electromagnetic fields. Any conductor system must be capable of carrying the full lightning current
- LPZOB This zone is an area where a direct hit is not possible, but high electromagnetic fields will be present. This zone is determined by the effectiveness of the structural system.
- LPZ1 Again, a direct hit in this area is not possible due to the screening measures applied. The electromagnetic field is much lower than LPZOA and LPZOB. It is in this zone where appropriate surge arresters may be fitted that will limit the value of surge current entering a facility.
- LPZ2 The value of surge current and electromagnetic field will be lower than that of LPZ1 when correct protection principles have been applied. It is in this area where sensitive electronic equipment may be safely installed
- Galvanic Coupling
- When a building is struck directly by lightning as indicated in Fig. 1, a large voltage develops across RA and the entire earth arrangement in building A will rise to a very high level, dependent on the amount of current applied. Building B’s earth arrangement will be at a much lower potential and the entire difference will be equalized via the communication cables.
When lightning current passes into the ground via a conductor Fig. 2 (tree trunk) a powerful electromagnetic force is set up due to the fast rise times of the strike.
This electromagnetic force then couples into any inductive loops that may be available in nearby buildings. When these currents equalize, damage usually occurs to the equipment.