An interesting order has been recently processed by our technicians. This time we were asked to calculate the necessary arrangements for lightning protection of stables in Smolensk region. We wrote several times about residential houses and "popular" objects, but we don't get such requests every day. We are sure you will be interested to learn more about the project!
An object: Stables presents itself a two-storey L-shaped building 25.3 meters long and 20.3 m wide (on the wide side). The height of the structure, together with the chimney reaches 9 meters. Shingles is used as roof coating. The soil at the site is accepted as sandy loam with the resistivity to current spreading of 150 ohm * m.
Task: it is necessary to make calculations and offer solutions for lightning protection and grounding.
As usual, we use the following regulatory documents for the calculations:
- Electrical Installation Code EIC 7th ed. (hereinafter - EIC);
- "Instructions for organization of lightning protection of buildings, structures and industrial communications"
Industry Standard 153-34.21.122-2003 (hereinafter IS);
- "Instructions for lightning protection of buildings and structures" AD 34.21.122-87 (hereinafter AD).
Taking into account the possible consequences mentioned in the IS document , the stables should be referred to the usual type of buildings, and from the point of AD - to the third category of lightning protection. According to the standards described in paragraph 1.7.103 EIC, the total resistance of spreading of ground electrodes of repeated groundings of the PEN-conductor of each overhead line at any time of the year should not exceed 10 ohms at the line voltage of 380 V of a three-phase power supply or 220 V of a single-phase power source. In this case, the shape of the object and its roof suppose protection against lightning discharges, made by the lightning protection mesh. Beside the mesh, lightning protection system also includes a down conductor and ground electrode.
The complex of measures to ensure the necessary requirements to the lightning protection system is represented by the following solutions:
- Installation of three air terminal masts, 4 meters high. Down conductors are organized using copper-bonded steel wire D = 8 mm, and all lightning rods are connected along the roof ridge. (See. Fig.1).
- Installation of the grounding device, which consists of five vertical electrodes D = 14 mm, 3 m long, united by the horizontal electrode (copper-bonded tape 30x4 mm). The distance from the electrode to the walls of the building is not less than 1 m, the distance between the electrodes is not less than 5 m, penetration is 0.5 - 0.7 meters.
Figure 1. Arrangment of lightning protection and grounding equipment. Protection zone
Calculation of resistance of a grounding device:
Vertical electrode resistance:
Where Pэкв - equivalent soil resistivity, Ohm*m;
L - vertical electrode length, m;
d - vertical electrode diameter, m;
T - deepening - the distance from the ground to the ground electrode system, m;
Where t - deepening of the electrode top, m
Horizontal electrode resistance:
where D - horizontal electrode diameter, m;
t - depth of the horizontal mesh, m;
Lгор- horizontal electrode length, m.
Impedance of the grounding device:
where n - number of kits;
kисп- Utilization ratio;
The design resistance of the grounding device is 6.21 Ohms, which is less than the required impedance of 10 Ohm.
The list of necessary equipment:
Implementation of the described events will provide a building, stables, as well as people and cattle with a reliable protection against direct lightning strikes.
Do you have questions about selecting, designing and calculation of grounding and lightning protection systems? Write us and we will help!