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Lightning rod (air termination section) angle of protection


Old IEC lightning rod angle of protection

Range of protection Technical dataThe angle of protection of lightning rods set up to provide protection from lightning to persons, electrical facilities, petroleum complexes, gas tanks and other types of plant and equipment is specified by IEC as 60º or less for general buildings, and slightly smaller at 45º for locations where hazardous materials such as explosives, flammable gas and liquids, etc., are handled, manufactured or stored. However, these specifications have been in use for a long time and do not take height into consideration. For this reason, the angle of protection is currently thought to be too large, and even inside the angle of protection cannot be considered completely safe.
The reason is that the basic data that were used when these specifications were produced was based on experiments with artificial lightning generation apparatus, and since the size of the electrical discharge generated is too small when compared with actual lightning, it has been found that the experiment data are different from the results of actual lightning observation.


New IEC lightning rod angle of protection

IEC standards enacted in 1990 were adopted as new IEC standards in 2003 (IEC A 4201). At that time, height and protection efficiency were taken into account for the angle of protection for lightning rods. As the height of the protected structure increases, the angle of protection decreases, and for structures of over 60m there is no specified angle of protection, regardless of the protection level. This is because a side-on lightning strike that hits the side of a building cannot be intercepted by a lightning rod when the height of the building is over 60m.
Protection level Protection efficiency Rolling sphere method Protection angle method (height: h) Mesh method (m)
R(m) 20m 30m 45m 60m over 60m
0.98 20 25° * * * * 5
II 0.95 30 35° 25° * * * 10
III 0.9 45 45° 35° 25° * * 15
IV 0.8 60 55° 45° 35° 25° * 20

An asterisk (*) means applicable only to rolling sphere and mesh methods.

Lightning rod angle of protection at protection level IV (protection efficiency 0.80)   Protective range of rolling sphere method
Lightning rod angle of protection at protection level IV (protection efficiency 0.80)   Protective range of rolling sphere method

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