Lightning is actually a visible discharge of static electricity within a cloud and also between clouds. The light protection system offered by us provides a means by which this discharge might leave or enter the Earth without actually passing through the damaging non-conducting parts of a structure, like those made of wood, brick, tile of- concrete. Such a lightning protection system does not prevent lightning from striking but provides a means for controlling it and preventing damage by providing a low resistance path for the discharge of lightning energy.
The Lightning Protection System has undergone many changes and today's lightning protection system exhibit the best in terms of design, materials and installation, thus valuable life and property can be well protected from nature's hazardous and exciting phenomenons like, lightning. Lightning is a unique form of energy and an expert can only install proper protection systems against it.
The BS6651:1992 norms states that the provision of conventional lighting protection system should be strictly followed.
There are certain principle design considerations of a conventional lighting system as per the BS 6651 norms, these are
- Air Termination Network
- Down Conductors
- Earth Termination Network
Air Termination Network
This phenomenon is applicable on high risk structures like, explosives factories, nuclear power plants wherein no part of the roof should be more than 2.5m from from an air termination conductor. This can be done by applying a 5m x 10m mesh to the roof. 10m x 20m Mesh 60 m.
Generally for most structures a mesh measuring 10m x 20m is actually sufficient. The range of air termination protection is considered to be 45 for heights up to 20m. Above this height the production zone is determined by the "rolling sphere method" i.e., 140m.
The location of the down conductor is majorly influenced by the architectural design. This is like, there has to be one down conductor after every 20m. These are evenly spaced at not more than a distance of 20m. These must be rooted as directly as is possible from the air termination to earth termination networks and the loop should not exceed eight times the width of it's open side.
Earth Termination Network
Every Down conductor should be provided with a separate Earth Termination. For testing purpose the provision should be made in each down conductor.
The BS6651norms mentions that the resistance to earth for complete lightning protection at any point should not exceed beyond 10 ohms. This norm also mentions that the combined length of the earth rod system should be no less then 9m, while each individual earth rod should be not less than 1.5m in length.
As soon as lightning protection system is struck, its electrical protection with respect to earth is considerably raised and if resistance provided by the down conductor is more than the other metal work on the structure, the discharge looks for alternative path to Earth by way of side flashing.
Thus, it is important that all the exposed metal work is bonded into the lightning protection installation.