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Lightning Conductor

There are many locations and buildings, which have to be protected from lightning damage. Storage location of inflammable material is an example. High rise buildings and structures housing equipment etc. also have to be protected as precautions taken for personnel safety is of little use in such places. A device which gives a good amount of protection and which has been in use is the Lightning Conductor.

The Lightning Conductor:
The Lightning Conductor which is also known as Lightning Rod or Air Terminal is one of the best known form of shielding device and has been in use in protecting buildings and facilities where protection is mandatory such as, storage tanks for petroleum products, warehouses for explosives etc. The main purpose of the lightning rod is to provide a point well above the structure to be protected with a very good, earthed connection so that the lightning energy gets diverted into ground without damaging the structure. It has no role in preventing a lightning occurrence.


Lightning Conductors must be exposed and should be placed at the highest levels. They may be painted for protection against corrosion. There is a code of practice on Lightning Conductor and its installation published by the Bureau of Indian Standards. Conformance to this will make the Lightning Conductor effective.


The earthing done for domestic power supply is not at all sufficient for lightning conductor earth. This is evident from the magnitude of currents involved in lightning which is more than two orders of magnitude higher than the domestic supply currents. However, because of the high voltage involved, proportionally heavy earthing is not needed as the voltage itself will drive it into ground.

Cone of Protection

This is a term used to describe the volume of protection offered and it provides a simple graphical tool for installing a Lightning Conductor protection system. Arrangement of a Lightning Rod showing the cone of protection is given in figure.



The ratio of height to radius of area expected to be protected defines the volume. The safe ratio is 1:1 (equalto 45° angle to either side) for sensitive installations and for others ratios as high as 1:1.75 are also used. When large buildings are to be protected a single rod will not suffice. Multiple rods with several earths are done in such cases. These rods are interconnected at the top of the building using thick copper, brass or GI strips of sufficient thickness and connections from several points are run to each earthing rod or grid. These interconnecting strips also provide an additional protection all along the length of the strip similar to the lightning rod.

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