Lightning Protection System Diagram: Components, Zones and Earthing
This is a free printable lightning diagram: download the diagram as SVG or open it and print to paper or PDF.
A lightning protection diagram illustrates the complete system of air terminations, down conductors, bonding connections, and earth electrodes that intercept a lightning strike and safely conduct its energy to ground.
A lightning protection system (LPS) does not prevent lightning from striking a structure — it provides a preferred, controlled path for the massive discharge current of a lightning strike (typically 30 kA, with extreme events exceeding 200 kA) to travel from the point of strike to the earth electrode without passing through the structure's fabric, occupants, or electrical systems.
An LPS is designed in accordance with IEC 62305 (international standard), BS EN 62305 (UK), or AS/NZS 1768 (Australia/NZ). A Lightning Protection Level (LPL) is assigned based on the risk assessment of the structure and its contents, ranging from LPL I (highest protection, for critical or high-risk structures) to LPL IV (lowest protection, for ordinary buildings with minimal risk).
The external LPS consists of three subsystems. The air termination network (formerly called lightning rods or Franklin rods) occupies the uppermost part of the structure — ridges, roof edges, parapets, and protruding features — and is designed to intercept the lightning channel. Positioning follows either the rolling sphere method, the mesh method, or the protective angle method, as specified in the applicable standard.
The down conductor network carries the discharge current from the air terminations to ground. Multiple parallel down conductors are required on larger structures to divide the current and reduce the inductive voltage gradient. Each down conductor must have a test point installed at approximately 1 m above grade to allow earth electrode resistance measurement without disconnecting the system.
The earth termination network consists of earth electrodes — typically horizontal ring conductors buried at the foundation perimeter, supplemented by vertical rods. The earth electrode resistance must meet the LPL requirement (typically below 10 Ω).
The internal LPS addresses secondary effects — electromagnetic pulse, conducted transients on electrical and data lines, and step potential within the structure. It consists of bonding conductors connecting all metallic services (water pipes, gas pipes, electrical earth, data cable shields) to an equipotential bonding bar, and surge protective devices (SPDs) on incoming electrical and data lines.
How to wire lightning diagram
- Conduct a risk assessment Assess the structure against the criteria in IEC 62305-2 or the equivalent national standard. The risk assessment considers the structure type and use, occupant density, consequence of failure, flash density for the location, and the dimensions of the structure. The output is the required Lightning Protection Level (LPL I–IV) or a risk figure that guides the decision to install or upgrade an LPS.
- Design the air termination network Using the rolling sphere, mesh, or protective angle method appropriate to the LPL, position air termination conductors or rods to intercept potential strike attachment points on ridges, roof edges, high points, and protruding features. The mesh size and sphere radius vary with LPL.
- Route down conductors Distribute down conductors around the building perimeter at intervals specified by the LPL (typically 10–20 m). Route conductors as straight and direct as possible to minimise inductance — avoid sharp bends and loops. Install a test point in each down conductor at approximately 1 m above grade.
- Install the earth termination network Install a ring earth electrode around the building perimeter, buried at a depth of 0.5 m minimum. Connect to the ring with vertical rods in high-resistivity soil. Measure earth electrode resistance at each test point — it should meet the LPL requirement (typically below 10 Ω).
- Implement equipotential bonding At each point where a metal service enters the building (water pipe, gas pipe, electrical conduit, telecommunications cable), install a bonding conductor connecting it to the main bonding bar. The main bonding bar connects to the LPS earth termination.
- Install surge protective devices Fit a Type 1 (Class I) SPD at the main service panel on each live conductor, neutral, and earth where required by the risk assessment. Install Type 2 SPDs at sub-panels and Type 3 at sensitive electronic equipment. Confirm SPD rating coordinates with the LPL discharge current requirement.
- Commission, test, and document Measure earth electrode resistance at all test points and record. Document the as-built LPS with photographs, conductor routes, test point locations, and measurement results. Provide the documentation to the building owner for the maintenance record.
Specifications
| Typical peak lightning stroke current | 30 kA (first stroke); up to 200 kA (extreme events) |
|---|---|
| Earth electrode resistance target (general) | ≤ 10 Ω |
| Rolling sphere radius — LPL I | 20 m |
| Rolling sphere radius — LPL II | 30 m |
| Rolling sphere radius — LPL III | 45 m |
| Rolling sphere radius — LPL IV | 60 m |
| Down conductor minimum cross-section (copper) | 50 mm² |
| Ring earth electrode burial depth (minimum) | 0.5 m |
Safety warnings
- Lightning protection systems must be designed and installed by a qualified lightning protection system specialist and must comply with IEC 62305, BS EN 62305, AS/NZS 1768, or the applicable national standard. Incorrect design or installation can increase risk rather than reduce it.
- No lightning protection system provides absolute immunity from all lightning strike damage. An LPS mitigates the risk of structural fire, physical damage, and injury by providing a controlled discharge path, but very large strike events or indirect effects may still cause damage.
- Never shelter under isolated trees, near metal fences or pipelines, or in open structures during an active thunderstorm. An LPS protects structures, not persons in open ground.
- SPDs have a finite lifespan and must be replaced following absorption of a large surge or after the service life indicated by the manufacturer. Check SPD status indicators regularly.
- All earth electrode measurements must be performed by competent personnel using a calibrated earth resistance tester, following a safe working procedure that isolates the system from any live connections during testing.
Tools needed
- Earth resistance tester (fall-of-potential or clamp-on type)
- Calibrated multimeter
- Tape measure and surveying equipment for rolling sphere calculations
- Cable crimping tool for conductor connections
- Conduit and masonry drill for routing and fixing
- Torque wrench for terminal connections
- Personal protective equipment (insulated gloves, eye protection)
Common mistakes
- Installing a single isolated lightning rod without a down conductor and earth electrode, leaving no controlled discharge path and potentially making the situation worse.
- Routing down conductors with sharp 90-degree bends, which significantly increases conductor inductance and the voltage gradient during a strike.
- Omitting equipotential bonding on incoming metallic services, leaving dangerous potential differences between the LPS earth and water or gas pipes.
- Failing to install SPDs, leaving electrical and electronic equipment unprotected from the conducted transients that are the most common cause of lightning-related equipment damage.
- Not documenting or testing the installed LPS, resulting in no baseline for future inspection comparisons and no proof of compliance.
Troubleshooting
- Earth electrode resistance exceeds acceptable limit
- Cause: High soil resistivity, insufficient electrode length or surface area, or poor electrode-to-soil contact due to dry or rocky conditions. Fix: Add additional vertical rods in parallel with the existing electrode to increase total surface area. In very high-resistivity soil, consider chemically enhanced electrodes or deep-driven rods. Re-measure after each addition until the target resistance is achieved.
- Visual corrosion on conductor connections
- Cause: Galvanic corrosion at bi-metallic junctions (e.g., copper conductor to aluminium roof) or general atmospheric corrosion, weakening the mechanical and electrical connection. Fix: Replace corroded connections with new fittings using appropriate anti-oxidant compound and bi-metallic transition clamps where dissimilar metals meet. Inspect all connections at the next scheduled maintenance interval.
- SPD status indicator shows fault condition
- Cause: The SPD has absorbed a surge and its thermal disconnector or varistor has operated, indicating the device has reached end of life and must be replaced. Fix: Replace the SPD with a new unit of the same or higher rating. Investigate whether the upstream Type 1 SPD also requires replacement. Do not leave the SPD in circuit in fault condition, as it will no longer provide surge protection.
Frequently asked questions
What is the rolling sphere method in lightning protection design?
The rolling sphere method is a mathematical model used to determine the protected volume around an air termination. Imagining a sphere of radius equal to the LPL striking distance (20 m for LPL I, 45 m for LPL IV) rolled across and around the structure, any part of the structure that the sphere can touch requires an air termination. Parts the sphere cannot touch (because the air termination intervenes) are considered protected.
How does an LPS earth electrode system work?
Earth electrodes provide a low-impedance path for the lightning discharge current to dissipate into the soil. A ring earth electrode — a horizontal conductor buried around the perimeter of the building foundation — is the most effective because it distributes current broadly and reduces the earth surface potential gradient around the structure. Vertical driven rods supplement the ring in high-resistivity soils.
What is equipotential bonding and why is it needed?
When a lightning current enters the earth termination of a building, it raises the local earth potential significantly. If metal services (water pipes, gas pipes, electrical cables) enter the building from elsewhere at a lower potential, a dangerous potential difference exists between them and the structure. Equipotential bonding connects all metallic services at the point of building entry to a common bonding bus, eliminating the potential difference.
What is a surge protective device and where is it needed?
A surge protective device (SPD) clamps the voltage on electrical or data conductors during a transient, diverting surge current to ground before it can damage connected equipment. SPDs are installed at the main service panel (Type 1/Class I for direct lightning attachment protection), at sub-panels (Type 2/Class II), and at sensitive equipment (Type 3/Class III for point-of-use protection).
How often should a lightning protection system be inspected?
IEC 62305 recommends inspection intervals based on the LPL and exposure category — typically every one to two years for higher-risk structures and every two to four years for lower-risk structures. Each inspection should include a visual check of all air terminations, conductors, and connections, and a measurement of earth electrode resistance at the test points.