ZANDZ technical center received a task to calculate lightning protection for a school in the Kaliningrad region. The building has large dimensions and a variable number of storeys. These facts suggest the use of a large number of lightning protection equipment to meet all the necessary standards of protection.
Our experts would have done so if not one feature: metal fencing is made around the perimeter of the roof, which can serve as an excellent natural lightning rod. It is only necessary to unite the fencing into a continuous system of down conductors and supplement it with artificial lightning rods. As we know, the elements of the roof, in addition to their primary purpose, can also perform the function of lightning protection.
Let's see what decisions were taken:
Task: Lightning protection of the building must be carried out in accordance with the following regulations:
- EIC 7th ed. Chapter 1.7
- IS 153-34.21.122-2003 "Instructions for lightning protection of buildings, structures and industrial communications" (hereinafter IS)
- AD 34.21.122-87 "Instructions for lightning protection of buildings and structures" (hereinafter AD)
The protected building is an ordinary structure in terms of lightning protection according to the IS and refers to Category 3 according to the AD.
Solution:protection of buildings against lightning strikes is carried out with the help of lightning rods. A lightning rod presents itself a device rising above the protected facility to divert the lightning current into the ground without entering the protected facility. It consists of a lightning rod directly perceiving the lightning discharge, down conductor and ground electrode system.
The complex of measures to ensure necessary requirements for the lightning protection system is represented by the following solutions:
- Fencing around the perimeter of the roof and the metal stairs are used as lightning rods and down conductors. It is necessary to provide a continuous electrical connection between them using a copper-bonded steel wire D = 8 mm and clamps ZZ-005-064.
- In addition, two air terminals-masts on three concrete foundations 4 m high and six rod lightning rods 4 m high, which are mounted to the wall are installed. It is considered that 0,5 of the rod length goes to the fixation.
- Down conductors with the use of copper-bonded wire D=8 mm, which are connected with the artificial ground electrode are put along the roof perimeter at the distance of not less than 20 m. Lightning rods are also interconnected for the organization of two down conductors from each lightning rod. Fixation of the down conductors on the roof is carried out with the help of clamps GL-11711 (0.6-1 m installation step). Fixation of down conductors to the well is carried out by means of clamps GL-11703A (0.6-1 m fixation step). Connection and branching of down conductors is carried out with the help of GL-11551A clamps.
The set of measures to ensure the necessary requirements to the grounding device is represented by the following solutions:
- A horizontal contour is put around the building. The contour is made of corrosion-resistant stainless copper-bonded steel tape with the cross- section 4x30 mm (GL-11075), laying depth 0.5 m, distance to the wall of the building 1 m.
- Connection of horizontal electrodes is carried out by using clamp ZZ-005-064.
- Down conductor is connected with the output of the copper-bonded tape from the ground with the help of clamp GL-11562A.
It is recommended to use the conductive structures of the building as down conductors: a metal frame, reinforcement mesh of reinforced concrete structures, glass unit fittings, etc. ensuring electrical contact over the entire height of the building.
The following source data are accepted for the calculation:
- The density of lightning strikes into the ground - 4 strikes / sq. km per year;
- The number of strikes into an unprotected object - 0.18 1/year, period - once in 5 years.
The results of lightning protection calculation performed by the software, developed by JSC "Energy Institute to the name of Krzhizhanovsky "(JSC" ENIN ") are presented in the table below:
|Object||Height of artificial lightning rods||Protection reliability||The number of strikes into an object, year-1||The number of breakthroughs into the object, year-1|
|Period of srikes, year||Period of breakthroughs, year|
|once in 5 years||once in 55 times|
Plan with the mounted elements of lightning protection and grounding
The list of the required materials is given in the chart:
In this example, it is proved that at the design stage of construction it is possible to apply solutions which will serve as a lightning protection. In the result, you will get a "light" design, not overloaded by dozens of kilometers of wire and dozens of lightning rods.
Please contact us for advice and calculations! ZANDZ technical specialists will surely take into account all the details and select the optimal design of grounding and lightning protection systems!