This material is the second publication from the series of articles by Eduard Meerovich Bazelyan "Truth about lightning protection mesh". In these articles, the author tells about all the explicit and implicit nuances associated with the calculation of reliability, design and operation of lightning protection mesh.
Due to many years of confusion, it is better to repeat once again that a mesh laid on a metal tile or other roofing containing grounded metal structures is practically useless. The lightning channel simply won’t notice the mesh that does not have any significant elevation above the roof. Further in the same chapter we will talk about the effectiveness of the mesh laid on the dielectric coating of the structure, for example, on slate or modern flexible fiberglass of some kind of mobile or temporary object.
It’s time and place to talk about standardized mesh sizes. The discussion has to be carried out historically, because the structural dimensions of the mesh have changed more than once and are quite noticeable, but always without any justification. In the already mentioned book of 1951, it is noted that the usual dimensions of the mesh are 5x5 m, but in the calculation given there its size was reduced to 4 m. Document CN 305-69 “Guidelines for the design and installation of lightning protection of buildings and structures”states that not linear dimensions of the mesh are standardized, but the square of its cell, which should not exceed 36 m2 and 150 m2 for lightning protection of the second and third categories, respectively (in the case of a square mesh it is 6x6 m and 12x12 m). Similar requirements are retained in document CN 305-77. However, there is a remark there there - the mesh can only be laid on a flat roof.
Finally, in the document “Instructions for Lightning Protection of Buildings and Structures RD 34.21.122-87” we will again see mesh sizes - not more than 6x6 m for lightning protection of the second category and 12x12 m for the third category. The area of mesh use is somewhat expanding. Now it can be used not only on flat roofs, but also on roofs with a slope of up to 1: 8.
This is the second part of the series of articles "Truth about lightning protection mesh". To read the material completely, you must sign up on the site.Do you have questions on calculation of lightning protection and grounding? Contact ZANDZ technical Center!