At the beginning of 2006, the new IEC standards for lighting protection, Parts 1 to 4 of the series IEC 62305 were published. A revision of the standards takes place every 3 to 4 years. We adopt the IEC 62305 standards which are harmonised in Asia and this series of standards are internationally approved. These standards include:
- IEC 62305-1: Protection against lightning part 1: General Principals
- IEC 62305-2: Protection against lightning part 2: Risk Management
- IEC 62305-3: Protection against lightning part 3: Physical damage to structure and life hazard
- IEC 62305-4: Protection against lightning part 4: Electrical and electronic systems within structures.
The technology was initially developed in the year 1752 when Benjamin Franklin first started experimenting with the lightning mechanism. As shown in Figures 1 and 2, the Franklin Rod offers a cone shaped protection based upon its installed height above the structure. It assumes a positive angle from projections and the structural components within the cone area are deemed to be protected against direct strikes.
The current recommendation for applying the cone is for structure of protective angle, a as a function of height, h depending on the class of lightning protection system. This is shown in Figure 3.
The lightning protection systems for this design method should be manufactured from materials possessing highly corrosion-resistive characteristics. The design concept of the Faraday Cage is very similar to the Franklin Rod and the theory of Rolling Sphere as shown in Figure 4. The Faraday Cage comprises of horizontal air termination where external down conductors descend vertically from the air terminations.
These should be horizontally bonded at set intervals. The structural steel of reinforcing bars, if bonded, may be used to conduct the lightning current. This technique however allows a pseudo random current flow of lightning current within the building. The vertical down conductors should be spaced around the perimeter of the structure.
The essence of the Rolling Sphere method is based on an imaginary sphere, typically 20m to 60m in radius for standard class of protection to roll over the structure. All surface contact points with this sphere are deemed to require protection against direct lightning strikes.