It is necessary to make calculations and make grounding and lighting protection project for the object.
Object: one section of an apartment block.
Soil: sand clay
Soil resisitivity: 100 Ohm*m
Than 10 Ohm will be used as a grounding device. All metal elements protruding over the roof of the building (ventilation shafts, metal ladders, etc.) must be connected to the building's metal structures
The calculations were performed in accordance with the EIC 7th ed., IS 153-34.21.122-2003 "Instructions for lightning protection of buildings, structures, and industrial communications" (hereinafter IS) and AD 34.21.122-87 "Instruction for lightning protection of buildings and structures" (hereinafter AD).
Apartment buildings refer to ordinary constructions in terms of lightning protection in accordance with the IS and to category 3 according to the AD. The required reliability of lightning protection system - 0.9.
According to EIC-7, p. 1.7.103 The total spreading resistance of the ground electrodes (including natural) of all repeated groundings of the PEN conductor of each overhead line at any time of the year should not exceed 10 ohms at line voltage of 380 V of the three-phase power supply or 220 V of a single-phase power source.
Lightning protection of the objest was performed by means of lightning protection mesh on the roof of the building with the installation of air-terminal masts for protection of shafts elevating over the roof level with the equipment installed inside. The size of the cell of the lightning protection mesh is not more than 10x10m. Type of mesh - copper-bonded steel with the diameter of 8 mm, thickness of the coating 70 micron (GL-11149).
Installation of mesh is carried out on flat surfaces with the help of GL-11711 clamp, on vertical surfaces - GL-11703A
The distance between the clamps - 0,8- 1,0 m. To connect the mesh over the length and in the mesh nodes, a universal clamp GL-11551A is used.
Air terminal mast are mounted on vertical surfaces with the help of holders
All metal elements, placed on the roof (ventillation shafts, ladders, fencing etc) should be connected to lightning protection mesh with the help of clamps GL-11545A.
The distance between the mesh and down conductors not more than 25 m. A horizontal electrode (GL-11149) should be laid every 20 m (height of the building) over the building's perimeter.
The grounding device is designed as a contour around the perimeter of the building. Horizontal conductor - copper-bonded steel tape 30x 4 mm (GL-11075). Copper bonded steel electrodes D=14 mm, L=3 m are used as vertical electrodes. Verical electrodes are installed in places of downdrop of down conductors. Distance from the building base not less than 1 m.
The results of the calculation performed by the software, developed by JSC "Energy Institute to the name of G. M. Krzizhanovsky" (JSC "ENIN"):
- the density of lightning strikes into the ground - 6 strikes / sq. km per year;
- the total number of strikes into the system in: 0.0066 (once in 910 years);
- the total number of breakthroughs (strikes directly into the object passing lightning rods) - 0.00051 (once in 1810 years);
- Protection reliability:0.923.
Calculation of grounding device resistance:
Resistance of a vertical electrode:
where ρeq - equivalent soil resistivity, ohm · m;
L - length of the vertical electrode, m;
d - vertical electrode diameter, m;
T- deepening - distance from the ground surface to the ground electrode, m;
Resistance of a horizontal electrode:
ρ - soil resistivity, Ohm* m;
b - horizontal electrode tape width ,m;
Lгор - horizontal electrode length, m.
where t - deepening of the electrode top, m
Impedance of the grounding device:
where n - number of kits;
Kисп - utilization ratio;
The design resistance of the grounding device is 0.74 ohms, which is less than the permissible resistance of 10 ohms.
The list of required materials:
Appendix: the project is available in DWG and PDF formats
Files in the formats DWG and PDF are available for downloading only for authorized users.
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