Concerning the lightning protection, it is very difficult to find such a confusing term as the lightning protection grid. Surprisingly, this is primarily associated not with the regulatory document but rather with its peculiar interpretation by the readers, especially by the authorities' representatives. The grid has been used to protect buildings and structures for many years.
E. M. Bazelyan, Dr. Sc. (Eng.), Professor;
Krzhizhanovsky Energy Institute, Moscow;
recognized Russian Expert in Earthing and Lightning Protection
1. BACKGROUND
The name of the section closely reflects the main aspect: the grid is designed only for the protection of buildings and structures having non-metal roofs. This is a very specific wording. It does not allow for any ambiguous interpretations.
2. THE GRID ON THE ROOF OF A MODERN BUILDING
It is known that, in order to provide protection against the direct lightning strikes, the lightning arrester should be much higher than the protected structure. The higher it is, the better the protection. The protection zones according to Instruction SO-153-34.21.122-2003 state that even with the protection reliability 0.9, the lightning arrester should be by at least 15% higher than the object, which is about 2 m for a 5-storey building.
3. WHEN WE USE THE GRID ACCORDING TO ITS INTENDED USE
Because of a long-term confusion, it is better to repeat that the grid installed on metal tiles or any other roof coating that contains the earthed metal structures is almost useless. The lightning channel will not notice the grid without any significant height over the roof.
4. CALCULATING THE PROTECTION RELIABILITY OF THE GRID
From the electrophysical standpoint, the grid is a multi-wire system, for which calculations may be performed, e.g. using the probabilistic technique that was developed almost 50 years ago by the Krzhizhanovsky ENIN and that is still in use in Russia. Using the technique, all protection zones were generated for the Lightning Protection Instruction SO-153-34.21.122-2003. The software is publicly available on the website.
5. THE REASON FOR A "STRANGE" GRID OPERATION
The basic indicator used in the lightning protection is the lightning collection radius. Its averaged value is usually taken as a 3-fold height of an on-ground structure, Ratt = 3h. The area of the lightning collection is limited by a closed curve spaced from the external boundary of the structure at the distance 3h.
6. RECOMMENDATIONS FOR THE DESIGNERS
The lightning protection grid is intended only to protect the personnel and equipment at the top floor of the building having a dielectric roof. It is pointless to install the grid on metal reinforced concrete plates or their waterproofing layer, but it is even more pointless to try to convince the representative of the authorities to stop using it.
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