During the construction of sewage treatment plants, in accordance with the current regulatory documents, it is necessary to comply with the lightning protection of the newly erected structure.
ZANDZ Technical Center received a request for the calculation of lightning protection and grounding systems for a building of a sewage treatment plant in Moscow region. Let’s see what solution was taken.
Source data:
- object: sewage treatment building;
- object sizes: 12 m х 6 m х 5,8 m;
- roof material: roof sandwich panel;
- materials of walls: metal corrugated sheets;
- soil resistivity – 150 Ohm*m.
Task:
- to provide measures to ensure the system of external lightning protection;
- calculate a grounding device with a resistance of less than 4 ohms.
Lightning protection and grounding of the building are carried out in accordance with:
- «Electric installation code» IEC 7 edition (hereinafter -EIC).
- «Instruction on arrangement of lightning protection of buildings, structures and industrial communications» IS 153-34.21.122-2003 (hereinafter – IS)
- «Instruction on arrangement of lightning protection of buildings and structures» AD 34.21.122-87 (hereinafter- AD).
The object belongs to the "ordinary" in terms of IS and category III of lightning protection in accordance with the AD.
The complex of measures to ensure the necessary requirements for the systems of lightning protection and grounding of the sewage treatment plant building is represented by the following solutions:
- According to IS СО 153-34.21.122-2003, p.3.2.1.2 the metal structure of the object (roof sandwich panel) is used as a lightning rod.
- The metal structure of the object – corrugated sheets is used as a down conductor.
- For equalization of potentials and connection of all metal communications, equipment and metal structures on the roof, installation of artificial down conductors, made of copper-bonded steel (copper coating thickness not less than 70 microns) of d8 mm wire (GL-11149), is performed.
- Installation of down conductors is carried out using a clamp GL-11747A - on the roof, GL-11704A - on vertical surfaces, GL-11514N - down drops on water pipe, GL-11545A - on the gutter. Clamp installation pitch 0.8-1.0 m.
- For connection of rolled products along the length and in nodes, the universal clamp GL-11551A is used.
- All metal elements placed on the roof (snow holders) must be attached to the down conductor using clamps GL-11545А.
- Transient resistance between all down conductors, metal sheets and panels should be not more than 0.05 ohms with mandatory annual monitoring of the latter before the beginning of a thunderstorm season, in accordance with AD 34.21.122-87, p.3.4.
- The connection of the metal structure (lightning rod) of the object to the grounding device is made at the corners of the object.
- Copper-coated steel electrodes 15 m long are used at the points of the down conductors and at the corners of the object as a vertical ground electrode. A copper-bonded steel tape with a cross-section of 30x4 mm, which unites all vertical electrodes, is used as a horizontal ground electrode. The distance to the foundation of the object is at least 1 m. The depth of the strip is 0.5 - 0.7 m.
- According to EIC-7 ed., P.7.7.55 - Grounding devices for protective grounding of electrical installations of buildings and structures and lightning protection of the 2nd and 3rd categories of these buildings and structures, as a rule, should be common.
- All reinforced concrete foundations should be used as natural grounding and attached to an artificial grounding device.
- An internal grounding circuit is made in the electrical room for equalization of potentials. The fastening of the tape to the surfaces is carried out using holders GL-11751A.
- The connection of the down-conductors to the grounding device is carried out with the help of clips ZZ-005-064.
Calculation of grounding device resistance:
Vertical electrode resistance:
where ρэкв – equivalent ground resistivity - 150 Ohm•m;
L – vertical electrode length - 15 m;
d – vertical electrode diameter - 0,014 m;
T – burying –distance from the ground surface to the ground electrode – 8 m;
where t – burying of the electrode top - 0,5 m
Horizontal electrode resistance:
where ρ – ground resistivity - 150 Ohm•m;
b - horizontal electrode length - 0,03 m;
h - depth of horizontal electrode burying - 0,5 m;
Lгор – horizontal electrode length - 27 m.
Complete resistance of the grounding device:
where n – number of sets, vertical ground electrodes - 4 pc., horizontal ground electrode – 1 pc.;
Kисп – utilization ratio 0,65;
Grounding device design resistance is 3,8 Ohm.
Equipment placement and protection zone are shown in Figure 1.
The list of equipment and necessary materials is given in table 1.
| условные обозначения | Type Codes |
| проволока стальная омедненная диаметром 8 мм | copper-bonded steel wire 8 mm in diameter |
| полоса стальная омедненная сечением 30*4 мм | copper-bonded steel tape with the cross section of 30*4 mm |
| универсальный зажим-соединитель для проволоки | universal connector terminal for wire |
| зажим хомут | clamp |
| зажим для подключения проводника | clamp for connecting conductor |
| подключение молниеотвода | connection of lightning rod |
| вертикальный заземлитель длиной 15 м | vertical ground electrode 15 m long |
| входная площадка | landing platform |
| резервуар | tank |
| фундаментная плита | foundation plate |
Figure 1 – Layout of grounding and lightning protection equipment for a sewage treatment building.
Table 1 – List of material needs
| № | Product item | Name | Q-ty, pc | Wight un., kg | Note |
| 1 | GL-11149-20 | GALMAR Copper-bonded wire (D 8 mm / S 50 mm²; coil of 20 meters) | 3 | 0,41 | Per meter |
| 2 | GL-11545A | GALMAR Clamp on gutter for down conductor (painted galvanized steel) | 30 | 0,112 | |
| 3 | GL-11551A | GALMAR Clamp for connecting down conductors (painted galvanized steel) | 20 | 0,07 | |
| 4 | GL-11747A | GALMAR Clamp on the roof covered with metal profile/corrugated steel for down conductor (painted galvanized steel) | 20 | 0,02 | |
| 5 | GL-11704A | GALMAR Clamp to the facade (painted galvanized steel) | 10 | 0,02 | |
| 6 | GL-11514N | GALMAR clamp on gutter for down conductor (tinned copper tape + stainless steel clamp) | 10 | 0,076 | |
| 7 | GL-11075-20 | GALMAR Copper-bonded tape (30*4 mm / S 120 mm²; coil of 20 meters) | 2 | 0,98 | За метр |
| 8 | ZZ-001-065 | ZANDZ Grounding coper-bonded threaded rod (D14; 1,5 м) | 40 | 2,00 | |
| 9 | ZZ-002-061 | ZANDZ Threaded coupler | 37 | 0,08 | |
| 10 | ZZ-003-061 | ZANDZ Starting tip | 4 | 0,07 | |
| 11 | ZZ-004-060 | ZANDZ Driving head for a breaker hammer | 8 | 0,09 | |
| 12 | ZZ-005-064 | ZANDZ Clamp for connecting conductor (up to 40 mm) | 11 | 0,16 | |
| 13 | ZZ-006-000 | ZANDZ Conductive grease | 4 | 0,10 | |
| 14 | ZZ-007-030 | ZANDZ Hydro-insulation tape | 4 | 0,40 | |
| 15 | ZZ-008-000 | ZANDZ Breaker hammer tip (SDS max) | 1 | 0,50 | |
| 16 | GL-11751A | GALMAR Clamp to the façade/wall for a flat down conductor (down conductor 30*4mm; galvanized steel with paint) | 3 | 0,04 |
Do you have questions on grounding and lightning protection of sewage treatment building? Contact ZANDZ Technical Center for help!
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