Lightning Protection
Lightning is a natural phenomenon which is formed as a result of a natural build-up of electrical charges within storm clouds which discharge to earth. The magnitude of the electric current created can range from around 3000 and 200,000 amps with potentials of 100 million volts. The calculated probability of structurally damaging lightning strikes is once in every 500 years. In general, a building with metal roof and wall cladding will provide the best overall protection against lightning, especially when internal electronic equipment which may be affected by the electromagnetic effects of lightning is taken into account. The main components of a lightning protection systems are:
It is the air termination networks which have the greatest interface with the roof cladding and consist of conductors on a 10 m x 20 m grid. Metal roof cladding provides a good air termination network.
The air termination network must be securely fastened to the down conductors, which should be at 20 m centres around the perimeter of the building. Structural steelwork or a reinforced concrete structure form effective down conductors.
These are connections between the down conductors and an earthing electrode which is driven into the ground. A detailed explanation of the above is given in BS 6651: 1999. The notes are intended to be for guidance only and it is recommended that the cladding system manufacturer be consulted for further information.
