How To Calculate the Zone of Protection for Lightning Protection and Earthing?

The installation of random rods alone is inadequate when it comes to the safeguarding of a structure against lightning strikes. The effectiveness of any design for lightning protection and earthing depends upon extremely precise engineering, one of which is the defining of the "Zone of Protection."

By grasping this notion, it is guaranteed that your Earthing and Lightning Protection System will be able to divert the currents that are dangerous into the ground without causing damage to the building's vulnerable parts.

What is the Zone of Protection?

A Zone of Protection is an intricate area around a lightning arrestor that considerably minimizes the chances of a direct lightning strike occurring. Basically, it is the "safe bubble" generated by the installation of lightning protection components. Anything that is outside this calculated zone will be prone to facing a direct lightning strike, no matter if you have a lightning grounding system in other parts of the roof.

Core Methods for Calculating the Zone of Protection

According to International standards such as IEC 62305-3, there are three main ways to design and estimate this area. The proper one to use will depend on the height and complexity of your building.

1. The Rolling Sphere Method (Universal Application)

This is the most mathematically robust method, suitable for all types of structures, especially complex geometries.

How it works:,
Imagine a giant sphere rolling over your building. Every point the sphere touches is a potential strike point. The spaces under the curve of the sphere (which the sphere cannot touch because it is resting on air terminals or the ground) are considered protected.

Calculation Parameters:
The radius of the sphere (r) depends on the Class of Lightning Protection System (LPS) required:

Class I: r = 20 meters (Highest protection)

Class II: r = 30 meters

Class III: r = 45 meters

Class IV: r = 60 meters

Tip:For a highly sensitive facility requiring Class I protection, you need denser air terminal spacing to prevent the smaller 20m sphere from touching the roof.

2. The Protective Angle Method (Simple Structures)

This method is ideal for simple, vertical rods protecting specific equipment or small buildings. It uses the height of the rod to determine a cone-shaped safe zone.
The Formula:
The protective angle (α) changes based on the height of the air terminal (h) relative to the surface being protected.

Height (h):The vertical distance from the tip of the rod to the surface you want to protect.

Angle (α):Derived from standard tables. For example, a Class III system might allow a 45° angle for a rod up to 20m tall.

You calculate the radius of protection at ground level using simple trigonometry:

Radius = h x tan(α)

3. The Mesh Method (Flat Surfaces)

For flat roofs, a lightning earthing system often employs a mesh cage. The protection is ensured if the mesh size complies with the LPS class (e.g., 5m x 5m for Class I).

Why Precision Matters in Earthing and Lightning Systems

If calculations are done incorrectly, then essential parts of the structure might remain unprotected. Besides, the grounding for lightning protection should be connected to those air terminals in such a way that there is a low-impedance path to the earth. In case the area is calculated properly but the earthing system for lightning protection is not strong enough, the energy may still result in side-flashing or internal damage.
These calculation methods align with global safety protocols. For detailed design parameters, we recommend referencing the IEC 62305-3 standard.

Trust Pioneer Power International For Your Connections

The first defense against the most unpredictable force of nature is the calculation of the Zone of Protection. No matter if you apply the Rolling Sphere or Protective Angle method, the accuracy must be guaranteed.

At Pioneer Power International, we specialize in designing and installing comprehensive lightning protection and earthing solutions. Our experts carry out a thorough risk assessment and work through the steps until the installation of a robust earthing and lightning system is completed to make sure your infrastructure is safe and up to the regulations.
Contact us today to secure your property with engineering-backed protection.

Frequently Asked Questions:

Can an earthing and lightning arrester be connected together?

Without a doubt, they need to be connected. The lightning protection earth and the electrical safety earth must be linked together to realize equipotential bonding, thus eliminating dangerous voltage differences during a strike.

What is the main purpose of a lightning arrester?

It catches the lightning bolt and takes the enormous electric current down to the earth through a safe route so that it does not go through the building's structure or wiring.

What is the "Zone of Protection" provided by a single lightning arrester?

For a single rod, this is mostly a cone-shaped volume that goes from the tip and extends downwards. The size of the cone at the bottom is determined by the height of the rod and the type of protection required.

How often do lightning protection and earthing systems need to be inspected or maintained?

The visual inspections should be done once a year. The detailed testing of the lightning grounding system (resistance measurement) is done every 11 to 24 months according to the environment and building class.