Standalone lightning rods and wires are used for Category I lightning protection facilities.
Distance Sв from the lightning rod to the protected Category I facility depends on the facility's height, grounding electrode structure and soil resistivity ρ as per RD 34.21.122-87, item 2.3.
For the facilities higher than 30 m, Sв from the lightning rod is determined as follows:
- minimum allowable distance to the facility should be at least 3 m, with soil resistivity not more than 100 Ohm*m with any grounding arrangement design.
- with soil resistivity < ρ ≤ 1000 Ohm*m for grounding arrangements consisting of one reinforced concrete pile, one reinforced concrete pole stub or deep pole of a reinforced concrete support with the length indicated in item 2.2a, b, the distance is defined using formula:
Sв = 3+ 0,01 (ρ—100);
- for a grounding arrangement consisting of four reinforced concrete piles or pole stubs located in the angles of a rectangle at the distance of 3-8 m from each other or in the reinforced concrete foundation of a arbitrary shape with the area of ground contact surface at least 70 m2 or artificial grounding electrodes specified in item 2.2g, Sв = 4 m.
For the facilities higher than 30 m, Sв from the lightning rod is increased by 1 m for each 10 m in excess.
The total length of current collectors and lightning rods, I, as well as of the grounding design and soil resistivity is considered for lightning wires as per RD 34.21.122-87, item 2.4.
With length l < 200 m, the least distance Sв, m, is equal to:
- with soil resistivity less than 100 Ohm*m, for the grounding electrode of any design provided in item 2.2, Sв = 3.5 m;
- with soil resistivity 100 < ρ ≤ 1000 Ohm*m, for the grounding electrodes consisting of a single reinforced concrete pile, one reinforced concrete pole stub, or deep pole of reinforced concrete support with the length shown in item 2.2a, b, it is defined using formula:
Sв = 3,5+0,003 (ρ-100),
for grounding arrangements consisting of four reinforced concrete piles or pole stubs located at the distance of 3-8 m from each other or artificial grounding electrodes specified in item 2.2.g, Sв = 4 m.
With total length of lightning rods and current collectors I = 200-300 m, the least allowable distance Sв should be increased by 2 m compared to the values defined above.
If you need to calculate and design the grounding arrangement for a Category I facility, contact the ZANDZ Technical Centerto obtain calculations free of charge!