The object of a lighting conductor system is to provide a direct path of least resistance to earth, for the strike and in doing so, prevent any side-flashing onto adjacent metalwork, or mains services i.e. electricity, gas or water etc.
The British Standard (BS66551/99) provides assessments on the “Need for Protection” for structures, based on the location, type of construction and the number of storms averaged for the area each year. However, other factors may require the need for possible protection to be considered, such as where there are explosive of highly flammable materials.
The installation of a conductor system will not prevent or attract a lightning strike, but if correctly installed will direct the current discharge safely to earth and protect the structure and occupants. The system will usually provide a grid network of roof conductors with down conductors spaced vertically around the building at 20 metre intervals each with an earth termination positioned at ground level to achieve the correct limits of impedance for protection.
This method has superseded the previous method, whereby a single conductor was positioned on the highest point of the building as this has now been proved not to be sufficient, a strike can occur to the side elevation of a building and by-pass a single conductor.
These standard recommendations should be particularly observed for public buildings, such as Libraries, Museums, Schools, Council Offices, Historic Buildings, Community Centers, High-rise Housing and many other structures where people congregate in significant numbers such as Churches, Cathedrals and Hospitals.
Having taken into account all the above information, the final decision to protect a building may be necessitated by the value of the contents or danger to life, should lightning strike the building.
More information can be obtained from the NICEIC website.