The ZANDZ Technical Center has received a request to calculate the lightning protection and grounding system for the box office. Our engineers have developed an optimal solution that will be discussed further.
Initial data:
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facility: a box office,
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dimensions: 19.7 m х 10.8 m х 3.475 m;
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ridge height: 4.59 m;
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soil resistivity 100 Ohm*m.
Task:
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Calculate the external lightning protection system.
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Calculate the grounding device.
Solution:
The activities have been performed according to:
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EIC, Rev. 7., SO 153 34.21.122 2003 Instructions for Mounting Lightning Protections of Buildings, Structures and Industrial Communications (hereinafter referred to as SO);
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RD 34.21.122-87 Instructions for Mounting Lightning Protection for Buildings and Structures (hereinafter referred to as RD).
The facility is classified as «conventional» according to SO and as Category III according to RD. The required lightning protection system reliability should not be less than 0.9.
A set of measures to meet the necessary requirements to the lightning protection system and grounding arrangement for the box office includes the following solutions:
1. The lightning protection of the facility is made using ridge lightning arresters (GL-11521SS) attached with clamps GL-11525 as well as using vertical elevations of current collectors by 0.5 m along the roof edges.
2. A copper-plated steel wire (copper coating thickness of at least 70 μm), d8 mm (GL-11149) is used as a current collector.
3. Current collectors are installed using clamp GL-11711 on the roof and GL-11703A on vertical surfaces. The clamp installation spacing is 0.8 to 1.0 m.
4. The multifunctional GL-11551A clamp is used to connect rolled products over the length and in assemblies.
5. All metal elements located on the roof should be connected to the current collectors.
6. 3 m copper-plated steel electrodes in the locations of current collector downdrops are used as vertical grounding electrodes. The copper-plated steel strip with a cross-section of 30 x 4 mm, combining all vertical electrodes, is used as a horizontal ground electrode. The distance to the facility foundation is at least 1 m. Strip deepening is 0.5 to 0.7 m.
7. According to the EIC, Rev. 7, item 1.7.55, Grounding devices for protective grounding of electrical installations for buildings and structures and Categories 2 and 3 and lightning protection of these buildings and structures usually shall be common.
8. If there are reinforced concrete structures, they should be connected to current collectors/to the grounding arrangement.
9. Connection to the grounding device is performed using ZZ-005-064 clamps.
The density of lighting discharge into the ground is 4 strikes/sq. km per year.
The total number of strikes into the system is 0.0084 (once every 119 years).
The total amount of breakthroughs (the strikes directly into the facility bypassing lightning arresters) is 0.00061 (once every 1639 years).
The system reliability is 0.928.
Ground terminal resistance calculation:
Vertical electrode resistance:
Верт - Vert
Экв - Eq
Ом - Ohm
where ρρeq – is equivalent soil resistivity, 100 Ohm·m;
L – is vertical electrode length, 3 m;
d – is diameter of the vertical electrode, 0.014 m;
T – is depth, i.e. the distance from the ground surface to the ground electrode, 2 m;
where t – is deepening of the top of the electrode, 0.5 m
Horizontal electrode resistance:
Гор - Hor
Ом - Ohm
where ρ – is soil resistivity, 100 Ohm·m;
b - is horizontal electrode width, 0,03 m;
h - is horizontal electrode depth, 0,7 m;
Lhor is horizontal electrode length, 18 m.
Electrical impedance of the grounding arrangement:
ЗУ - GA
Ом - Ohm
where n is a number of sets, vertical grounding arrangements - 2 pcs, horizontal grounding arrangement - 1 pc;
Kutil is utilization rate, 0.81.
The calculated resistance of the grounding arrangement is 7,36 Ohm.
The equipment layout and the protection zone are shown in Fig. 1.
Условные обозначения - Legend
Figure 1. Equipment layout.
The list of equipment and necessary materials is provided in Table 1.
Table 1. List of needed materials.
| № | Part number | Name | Quantity, pcs. | Unit weight, kg | Note |
| 1. | GL-11521SS | GALMAR 2 m lightning rod for mounting in threaded holders (M16; stainless steel) | 2 | 10,00 | |
| 2. | GL-11525 | GALMAR Air terminal crest holder (M16 thread; conductor terminal of d10 mm; bronze) | 2 | ||
| 3. | GL-11149-50 | GALMAR Copper-plated wire (D 8 mm/S 50 mm²; 50-meter bundle) | 2 | 0,41 | Вес 1 м |
| 4. | GL-11551A | GALMAR Conductor connection clamp (painted zinc-plated steel) | 10 | 0,07 | |
| 5. | GL-11747A | GALMAR Conductor roof clamp for the roof coated with metal shape / corrugated sheeting (painted galvanized steel) | 110 | 0,05 | |
| 6. | GL-11703A | GALMAR Current collector facade clamp providing 15 mm elevation of the collector over the clamp (painted zinc-plated steel) | 10 | 0,02 | |
| 7. | GL-11075-20 | GALMAR Copper-plated strip (30 * 4 mm/ S 120 mm²; 20-meter strip bundle) | 1 | 0,98 | Weight per 1 m |
| 8. | ZZ-001-065 | ZANDZ Copper-plated threaded grounding rod (D14; 1,5 m) | 4 | 2,00 | |
| 9. | ZZ-002-061 | ZANDZ Threaded coupling | 3 | 0,08 | |
| 10. | ZZ-003-061 | ZANDZ Termination | 2 | 0,07 | |
| 11. | ZZ-004-060 | ZANDZ Guide head for jackhammer attachment | 1 | 0,09 | |
| 12. | ZZ-005-064 | ZANDZ Conductor connection terminal (up to 40 mm) | 5 | 0,312 | |
| 13. | ZZ-006-000 | ZANDZ Conductive grease | 1 | 0,10 | |
| 14. | ZZ-007-030 | ZANDZ Waterproofing tape | 2 | 0,40 | |
| 15. | ZZ-008-000 | ZANDZ Attachment to the hammer (SDS max) | 1 | 0,50 |
Do you have any questions about grounding and lightning protection of the box office? Please contact the ZANDZ Technical Center!
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