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Lightning Rod Protection Zone Calculator: Radius by the Rolling Sphere Method
The calculator works out the radius of the protection zone of a single lightning rod by the rolling sphere method under DSTU EN 62305-3: enter the rod height, the protection class and the object height, and you get the radius and a diagram. There is also a reverse mode: from the required radius the calculator finds the minimum height of the rod.
Contents
Lightning rod protection zone calculator
Choose the mode: the radius from the rod height, or the height from the required radius. The lightning protection system class sets the sphere radius: I — 20 m, II — 30 m, III — 45 m, IV — 60 m.
A preliminary calculation for a single rod; it does not replace a lightning protection design under DSTU EN 62305-3, which accounts for the shape of the object, several rods and risk.
Request a calculation and priceHow to use the calculator
- choose the calculation mode and the protection class; if the class is unknown, it is set by the design or a risk assessment under DSTU EN 62305-2;
- enter the rod height h above ground in metres; if an object at some height must be protected, give it as hx, and leave 0 for protection at ground level;
- in the “height from the required radius” mode, enter the radius of the circle to be protected and its height hx: the calculator finds the smallest rod height;
- the diagram shows the rod, the protection zone under the sphere arc and the object at height hx.
How the protection radius is calculated
The rolling sphere method pictures lightning as a sphere of radius R rolling over the ground and over structures. The protected space is the space the sphere does not touch. The sphere radius depends on the lightning protection system class.
For a single rod of height h not greater than R, the protection radius at ground level is r0 = √(h · (2R − h)). At a height hx the radius is smaller: rx = r0 − √(hx · (2R − hx)). If the rod is taller than the sphere radius, h = R is used in the calculation, because above that the protection zone no longer grows.
Protection radius at ground level by class
The table shows the protection radius r0 of a single rod of various heights by the rolling sphere method. The values are calculated with the formulas above; for a rod taller than R, h = R is used.
| Rod height h, m | Class I (R = 20 m), m | Class II (R = 30 m), m | Class III (R = 45 m), m | Class IV (R = 60 m), m |
|---|---|---|---|---|
| 10 | 17.32 | 22.36 | 28.28 | 33.17 |
| 15 | 19.36 | 25.98 | 33.54 | 39.69 |
| 20 | 20.00 | 28.28 | 37.42 | 44.72 |
| 30 | 20.00 | 30.00 | 42.43 | 51.96 |
| 40 | 20.00 | 30.00 | 44.72 | 56.57 |
A preliminary calculation for a single rod, without the shape of the object.
What the calculator does not account for
The calculator gives a preliminary result for one vertical rod in the open. A lightning protection design under DSTU EN 62305-3 accounts for the shape and material of the object, several air-termination elements, a mesh or wires, and a risk assessment.
The choice between the rolling sphere, protection angle and mesh methods is covered in the article calculating a lightning rod’s protection zone, and how to choose a lightning rod in lightning protection of masts and towers. Lightning rods on multi-sided poles: lightning protection of masts. On the change of standards: which lightning protection standards apply.
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Frequently asked questions about a lightning rod’s protection zone
What is a lightning protection system class?
It is a protection level I–IV under DSTU EN 62305-3, from the highest to the lowest. Each class has its own sphere radius: 20, 30, 45 and 60 m. The class is chosen by the design or a risk assessment.
How does the rolling sphere method differ from the protection angle method?
The rolling sphere is more accurate for tall rods and complex object shapes. The angle method is simpler but limited by the rod height: each class has a limit of application.
Why is the protection radius at the object height smaller?
The protection zone narrows with height: the higher the point to be protected, the closer to the rod it must be. So for an object on a roof the radius is smaller than at ground level.
Can one lightning rod protect a large object?
Only within the sphere radius: above R the rod height no longer enlarges the zone. Larger objects need several rods or another system, which the design determines.
Does the calculator replace a lightning protection design?
No. It is a preliminary calculation for one rod. The final decision is made by the design under DSTU EN 62305-3.
Related products: Lightning protection masts and air-termination rods · Steel structure design (structural and detail drawings) · Street lighting columns
More on this topic: Lightning Protection Norms: Why the Old Standard Was Withdrawn and What Applies Now · Calculating a Lightning Rod's Protection Zone: Methods and an Example · Lightning Protection of Masts and Towers: Choosing a Lightning Rod · A Steel Mast as Air-Termination and Down-Conductor per DSTU EN 62305-3 · Lightning Protection Inspection and Maintenance: Intervals, Checks, Records · Lightning Rod, Air Terminal, Lightning Protection: What's the Difference
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