BS EN 62305 is the British and European standard for protection against lightning. It consists of four parts: Part 1 (General principles) covers the physics of lightning and the scope of protection measures. Part 2 (Risk management) provides the methodology for assessing the risk of lightning damage and determining whether protection is needed. Part 3 (Physical damage to structures and life hazard) covers the design and installation of lightning protection systems (air termination, down conductors, and earth termination). Part 4 (Electrical and electronic systems within structures) covers protection of internal systems against the electromagnetic effects of lightning, including surge protection. The standard replaced the previous BS 6651 in 2006.

How is a lightning protection risk assessment carried out?

A risk assessment to BS EN 62305-2 evaluates the probability of a lightning strike and the consequences if one occurs. The assessment considers: the geographical location and local thunderstorm frequency (measured in lightning flash density — strikes per square kilometre per year), the size and height of the structure, the type of construction (steel frame, reinforced concrete, timber), the nature of the contents (people, flammable materials, electronic equipment, cultural heritage), the type of services entering the building (overhead or underground power, telecoms), and the consequences of damage (loss of life, public service disruption, economic loss). The output is a risk value (R) for each type of loss, compared against a tolerable risk level. If R exceeds the tolerable level, lightning protection is required. The level of protection (Class I to IV) is determined by how much risk reduction is needed.

What is an earth termination system?

The earth termination system is the part of the lightning protection system that disperses the lightning current into the ground. It must provide a low-impedance path to earth to ensure the lightning energy is safely dissipated. Common earth termination arrangements include: earth rods (vertical copper or copper-clad steel rods driven into the ground), ring earth electrodes (a bare copper conductor buried around the perimeter of the building), and foundation earth electrodes (conductors embedded in the concrete foundations of the building during construction). The earth termination system must achieve an earth resistance as low as practicable — BS EN 62305-3 recommends a target of 10 ohms or less for each earth electrode. The earth termination system of the lightning protection system must be bonded to the main earthing terminal of the electrical installation.

When is lightning protection required by law?

There is no specific UK law that requires lightning protection for all buildings. However, several regulations create a duty to assess the risk and provide protection where necessary. The Regulatory Reform (Fire Safety) Order 2005 requires a fire risk assessment that should consider lightning as an ignition source. The Health and Safety at Work etc. Act 1974 requires employers to ensure the safety of employees and others — where lightning poses a foreseeable risk, protection may be required. The Electricity at Work Regulations 1989 require that electrical systems are maintained to prevent danger. Building Regulations Approved Document B (Fire Safety) may require lightning protection for certain building types. In practice, lightning protection is most commonly required for: tall buildings, buildings with large footprints, buildings storing flammable materials, buildings providing essential public services (hospitals, fire stations), and buildings of cultural or historical significance.

How often should a lightning protection system be tested?

BS EN 62305-3 recommends testing at intervals not exceeding: 1 year for structures containing explosive materials or where the consequence of a strike is particularly severe, 2 years for structures with a Class I or II level of protection, and 4 years for structures with a Class III or IV level of protection. Testing should also be carried out after any known lightning strike to the structure, after any modification to the building or lightning protection system, and after any damage is observed. Testing includes visual inspection of all components (air termination, down conductors, bonds, earth termination), continuity testing of all conductors and bonds, and earth resistance testing of the earth termination system.

TECHNICAL GUIDE

Lightning Protection: BS EN 62305, SPDs, and Earth Termination

A practical guide to lightning protection for UK electricians. Covers BS EN 62305, risk assessment methodology, surge protection devices under BS 7671 Chapter 44, earth termination systems, and when lightning protection is required.

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12 min readUpdated 2026-06-10Andrew Moore, Founder of Elec-Mate

Written and reviewed by Andrew Moore, founder of Elec-Mate, against BS 7671:2018+A4:2026, IET Guidance Note 3 and the IET On-Site Guide.

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BS EN 62305-2 risk assessment for lightning protection systems

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BS EN 62305-2 Key Formulae

Ad = L\u00D7W + 2(3H)(L+W) + \u03C0(3H)\u00B2

Ad= Equivalent collection area (m²)

Nd= Ng × Ad × Cd × 10⁻⁶ — expected strikes per year

E= 1 − RT/R — required protection efficiency

RT= Tolerable risk (10⁻⁵ per BS EN 62305-2 Table 7)

Refs= BS EN 62305-1:2011, BS EN 62305-2:2012, BS EN 62305-3:2011, BS EN 62305-4:2011, IEC 62305

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Key Takeaways

1Lightning protection systems in the UK are designed and installed in accordance with BS EN 62305 (Protection against lightning), which consists of four parts covering general principles, risk management, physical damage protection, and electrical and electronic systems protection.
2A lightning protection risk assessment to BS EN 62305-2 determines whether a structure needs lightning protection and what level of protection (I to IV) is required based on the building type, contents, occupancy, and consequences of a strike.
3Surge Protection Devices (SPDs) protect the electrical installation from transient overvoltages caused by lightning. BS 7671 Chapter 44 sets out the requirements for SPD selection and installation within the electrical installation.
4The earth termination system is the foundation of any lightning protection system. It must provide a low-impedance path to earth — typically using earth rods, ring earth electrodes, or foundation earth electrodes.
5Lightning protection systems must be inspected and tested regularly — annually for critical structures and at intervals not exceeding 4 years for general buildings, in accordance with BS EN 62305-3.

01 · Technical Guide

Lightning Protection: What Every Electrician Needs to Know

The UK experiences approximately 200,000 to 300,000 lightning strikes per year. While most strikes occur in open countryside, strikes to buildings and structures cause fires, structural damage, electrical installation damage, destruction of electronic equipment, and risk to life.

A lightning protection system (LPS) provides a preferential path for the lightning current to follow from the point of strike to earth, bypassing the building structure and its contents. The system consists of an air termination network (the conductors on the roof that intercept the lightning), down conductors (that carry the current to ground), and an earth termination system (that disperses the current into the ground).

This guide covers the BS EN 62305 standard, risk assessment methodology, surge protection devices (SPDs) under BS 7671 Chapter 44, earth termination requirements, when lightning protection is required, and inspection and testing.

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02 · Technical Guide

BS EN 62305: The Lightning Protection Standard

BS EN 62305 is the comprehensive standard for lightning protection in the UK and Europe. It replaced the previous BS 6651 in 2006 and consists of four parts:

Part 1: General principles — covers the physics of lightning, damage mechanisms, and the scope of protection measures. Provides the foundation for understanding why protection is needed and what it achieves.
Part 2: Risk management — the methodology for assessing lightning risk and determining whether protection is needed. This is the starting point for any lightning protection project.
Part 3: Physical damage and life hazard — the design and installation of the structural lightning protection system: air termination, down conductors, earth termination, equipotential bonding, and separation distances.
Part 4: Electrical and electronic systems — protection of internal electrical and electronic systems from the electromagnetic effects of lightning. This includes surge protection, screening, and routing of services.

03 · Technical Guide

Lightning Protection Risk Assessment

The risk assessment to BS EN 62305-2 is the first step in any lightning protection project. It determines whether protection is needed and, if so, what level of protection is required.

Lightning flash density — the number of lightning flashes per square kilometre per year at the building location. In the UK, this ranges from approximately 0.2 (northern Scotland) to 2.0 (south-east England).
Collection area — calculated from the building dimensions (length, width, height). Taller buildings have a larger collection area and are more likely to be struck.
Consequence analysis — what happens if the building is struck? The assessment considers loss of human life, loss of public service, loss of cultural heritage, and economic loss.
Protection level — if protection is required, the level (Class I to IV) is determined by the risk reduction needed. Class I provides the highest level of protection (98% efficiency), Class IV the lowest (80% efficiency).

The risk assessment is typically carried out by a specialist lightning protection contractor, but electricians working on commercial and industrial projects should understand the process and be able to advise clients on the need for assessment.

04 · Technical Guide

Surge Protection Devices (BS 7671 Chapter 44)

While the structural lightning protection system (to BS EN 62305-3) protects the building itself, the electrical installation inside the building needs its own protection from transient overvoltages. This is where Surge Protection Devices (SPDs) come in, governed by BS 7671 Chapter 44.

Type 1 SPDs — installed where the building has a lightning protection system or is fed by an overhead supply line. These handle the highest energy surges (direct lightning current). Installed at the main distribution board.
Type 2 SPDs — the standard choice for most installations. They protect against switching surges and indirect lightning effects. Installed at the consumer unit or main distribution board.
Type 3 SPDs — fine protection for sensitive equipment. Installed close to the equipment being protected (at the socket or within the equipment's supply circuit).

BS 7671 Chapter 44 sets out when SPDs are needed. Under Regulation 443.4.1, protection against transient overvoltages shall be provided where the consequence caused by the overvoltage could result in (a) serious injury to, or loss of, human life, or (c) significant financial or data loss — limb (b) having been deleted by the BS 7671:2018+A2:2022 Corrigendum of May 2023. For all other cases, protection shall be provided unless the owner of the installation declares it is not required because any loss or damage is tolerable and they accept the risk of damage to equipment and any consequential loss. In practice, SPDs are now installed in most new domestic and commercial installations.

05 · Technical Guide

Earth Termination Systems

The earth termination system is the foundation of the lightning protection system. Its purpose is to disperse the lightning current safely into the ground with the lowest possible impedance.

Earth rods — vertical copper or copper-clad steel rods driven into the ground to a depth of 2.4m or more. Multiple rods may be needed to achieve the target earth resistance of 10 ohms or less.
Ring earth electrode — a bare copper conductor (minimum 50mm cross-section) buried at least 0.5m deep around the perimeter of the building. This provides a distributed earth termination with low impedance.
Foundation earth electrode — conductors embedded in the reinforced concrete foundations during construction. This is the most effective earth termination but can only be installed during the building phase.

The lightning protection earth termination must be bonded to the main earthing terminal of the electrical installation to ensure equipotential bonding. This prevents dangerous potential differences between the lightning protection system and the electrical installation during a strike.

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06 · Technical Guide

When Lightning Protection Is Required

Lightning protection is most commonly required for:

Tall buildings — buildings over 20m are significantly more likely to be struck and typically require protection.
Buildings with large footprints — warehouses, factories, and distribution centres have a large collection area.
Buildings storing flammable or explosive materials — petrol stations, chemical stores, munitions facilities.
Essential public services — hospitals, fire stations, data centres, telecommunications facilities.
Buildings of cultural or historical significance — churches, listed buildings, museums, galleries.
Isolated structures — buildings on hilltops or in exposed positions with no surrounding structures of similar or greater height.

For most domestic properties in the UK, a full structural lightning protection system is not required. However, SPDs at the consumer unit are increasingly standard practice under BS 7671 Chapter 44.

07 · Technical Guide

Inspection and Testing of Lightning Protection Systems

Lightning protection systems must be regularly inspected and tested to ensure they remain effective. BS EN 62305-3 specifies the following intervals:

Visual inspection — check all visible components for physical damage, corrosion, loose fixings, and broken conductors. Pay particular attention to bonds, test clamps, and the junction between down conductors and the earth termination.
Continuity testing — test the continuity of all conductors and bonds using a low-resistance ohmmeter. The resistance of each down conductor from air termination to earth termination should not exceed 0.2 ohms.
Earth resistance testing — measure the resistance of each earth electrode using the fall-of-potential method or a clamp-on earth tester. The target is 10 ohms or less per electrode.

08 · Technical Guide

For Electricians: Lightning Protection Opportunities

Lightning protection is a specialist area, but general electricians can add value by understanding the basics, advising clients on SPD installation, and carrying out the electrical aspects of lightning protection work.

SPD Installation

Installing SPDs at consumer units and distribution boards is within the scope of a general electrician. Understanding BS 7671 Chapter 44 and the risk assessment process enables you to recommend and install SPDs as part of new installations and upgrades.

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Lightning Protection: BS EN 62305, SPDs, and Earth Termination

Lightning Protection Calculator

Building Dimensions

Environment and Construction

Occupancy and Protection

Incoming Services

Key Takeaways

Lightning Protection: What Every Electrician Needs to Know

Get the BS 7671 A4:2026 Cheat Sheet — free

BS EN 62305: The Lightning Protection Standard

Lightning Protection Risk Assessment

Surge Protection Devices (BS 7671 Chapter 44)

Earth Termination Systems

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When Lightning Protection Is Required

Inspection and Testing of Lightning Protection Systems

For Electricians: Lightning Protection Opportunities

SPD Installation

EIC Certificate

Install and certify SPDs with confidence

Frequently Asked Questions About Lightning Protection

What is BS EN 62305?

How is a lightning protection risk assessment carried out?

What are SPDs and why does BS 7671 Chapter 44 require them?

What is an earth termination system?

When is lightning protection required by law?

How often should a lightning protection system be tested?

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