Modern molding workshops comprise complex melting and molding equipment as well as process automation systems imposing strict requirements to support the required level of power supply and protection against possible voltage surges. Lightning protection is a measure to support seamless operation of a molding workshop. Its aim is to prevent a lightning strike and protect the sensitive equipment located in the workshop from interference in case of secondary lightning effects.
Please find the calculation example for the lightning protection system for a steel molding and processing workshop performed by the ZANDZ.com technical specialists.
The activities were conducted in accordance with the Electrical Installations Code (EIC), Rev. 7, Chapter 1.7, SO 153-34.21.122-2003 "Guidelines for Arrangement of Lightning Protection of Buildings, Structures, and Industrial Utilities" (hereinafter referred to as SO), and RD 34.21.122-87 "Guidelines for Arrangement of Lightning Protection of Buildings and Structures" (hereinafter referred to as RD).
The facility belongs to Class III according to RD. The system reliability shall be at least 0.9.
Design of Lightning Protection for a Molding and Processing Workshop
Upon the customer's request, a lightning grid made using 8 mm steel zinc-plated wire was used as a lightning arrester. The grid step is not more than 10 x 10 m.
Metal caps should be provided on all air shafts that will function as natural lightning arresters.Zinc-plated steel wire d8 mm (ZZ-502-008) is used as a current collector.
Current collectors are installed using holder ZZ-202-015 on flat roof, ZZ-202-003 on ramparts and vertical surfaces. The clamp spacing is 0.8 to 1.0 m.
All metal elements located on the roof should be connected to the сurrent collector using clamps ZZ-202-006. Stairs and railings are attached using clamp ZZ-202-010.
The facility's foundation and every 20 m by height are banded with current collectors to provide the current collector banding along the perimeter to equalize the potentials.
Multi-purpose clamp ZZ-202-011 is used to connect the rolled products over the length and in assemblies.
The current collector is connected to the grounding arrangement using clamps ZZ-202-013.
Design of Grounding for a Molding and Processing Workshop
According to RD 34.21.122-87, item 2.26, 3 m vertical zinc-plated steel electrodes are used as a grounding arrangement. A galvanized steel strip with a cross-section of 40 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.
Rods are connected to the bar using clamps ZZ-202-012.
According to the EIC, item 1.7.103, total dissipation resistance of ground terminals (including natural ones) of all repeated groundings of the PEN wire of each high-voltage line in any season of the year shall not exceed 5, 10 and 20 Ohm, respectively, with linear voltages of 660, 380, and 220 V of a three-phase source or 380, 220, and 127 V of a single-phase source. The dissipation resistance of the ground terminal for each repeated grounding electrode shall not exceed 15, 30, and 60 Ohm, respectively, with the specified voltages. With soil resistivity ρ > 100 Ohm*m, said standards may be increased by 0.01 • ρ times, but not more than by 10 times.
According to RD, item 1.8, artificial ground terminals shall be located under the asphalt coating or in a unfrequented spots (on lawns, at the distance of 5 m or more from soil roads and pavements, etc.).
According to EIC-7, item 1.7.55, grounding arrangement intended for protective grounding of electrical installations for buildings and structures and the 2nd and 3rd categories lightning protection of these buildings and structures, as a rule, shall be common.
If there are reinforced concrete structures, they should be connected to current collectors/to the grounding device.
All grounding arrangements should be interconnected using clamps ZZ-202-012.
Grounding arrangement resistance calculation:
Calculation of Grounding Arrangement Resistance
Vertical electrode resistance:
Верт - Vert
Экв - Eq
where ρeq is soil resistivity, Ohm*m;
L is vertical electrode length, m;
d is vertical electrode diameter, m;
T is depth, i.e. the distance from the ground surface to the ground terminal, m;
Resistance of a horizontal electrode:
Гор - Hor
where ρ is soil resistivity, Ohm*m;
b is horizontal electrode width, m;
h is horizontal electrode depth, m;
Lhor is horizontal electrode length, m.
where t is deepening of the top of the electrode, m.
Total resistance of the grounding arrangement:
ЗУ - GA
Исп гр - Util
where n is number of sets;
kutil is utilization ratio
Верт - Vert
Гор - Hor
ЗУ - GA
Ом - Ohm
The estimated resistance of the grounding arrangement is 1.37 Ohm.
Зенитные фонари - Roof light
План кровли - Roof Plan
Водосточные воронки - Roof gulley
Лестница металлическая - Metal ladder
Lightning protection layout for a molding and processing workshop (full-size layout is available here)
List of required materials
Do you have any questions about lightning protection for the cadet school or other facilities? Please, contact the ZANDZ Technical Center!
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