I think you need to be a little clearer in what you are asking and trying to achieve.
Are you trying to place lightning dods on the highest points of the building to attract lightning to set locations from which you then provide heavy conductor connections directly to earth so that you control the path of lightning currents rather than allowing them to pass anywhere they like through the building structure. This is lightning protection and is protection for the structure. It is suaually accomplished using air terminals on the highest part of the building with one or more down conductor connections into a buried earth grid. You can get some guidance on the coverage of air terminals from standards such as AS1768 or equivalent other British, intenational or American standards. It may also be worth talking to lightning protection experts such as Erico as there are many types of lightning conductors, other than simple rods, which provide improved areas of coverage.
Are you trying to connect lightning devices to electrical systems which may have components outdorrs and subject to lightning strike in order to conduct the high impulse voltage to ground to pretect internal electrical equipment from the excessive voltage spike. This is lightning arresting.
Thanx for the clarification, my problem is about lightning protection as the heading states. I know it is accomplished by using air terminals.
My problem is to know if there is a formula to calculate the maximum area one air teminal should cover, Assume the building has four point of the same level of which i can put air terminal, should i put air terminal in all points i must make some calculations to know how many i should connect.
Also give me the way i should contact this expert ERICO.