What is a lightning protection system?
The external and internal halves of an LPS, the parts that make one up, where IEC 62305-3 specifies each part, and what NFPA 780 and AS 1768 call them. For engineers who specify one and the owners who pay for it.
A lightning protection system (LPS) is the complete set of measures that intercepts a lightning strike, conducts it safely to earth, and protects the structure, the people inside it and its electrical systems.
It is not a single device but a coordinated whole: something to catch the strike, a clear path to carry the enormous current down to ground, an earth system to disperse it into the soil, and internal measures to stop that current causing damage on its way through.
The physical LPS is specified under Part 3 of IEC 62305, the international lightning protection standard. Crucially, an LPS is never one-size-fits-all. The standard works from risk: the type of structure, how exposed it is, what it contains and who relies on it all decide whether an LPS is needed at all and, if so, how demanding it must be. This guide is about the parts: the two halves of an LPS, the components that make each one up, and where the standard specifies each component. Whether a structure needs an LPS is decided by the IEC 62305-2 risk assessment, and the order in which the parts are designed is in lightning protection system design.
IEC 62305 is not the only rulebook. In the United States the installation standard is NFPA 780, current in its 2026 edition, and in Australia it is AS 1768:2021. They describe the same physical system in different words and place it by different rules, so this guide covers what each one asks for below.
External and internal LPS
Every lightning protection system has two parts that work together, and it helps to keep them distinct because they defend against different things.
The external LPS catches the strike and gets rid of it. Its job is to give the lightning current a deliberate, low-impedance path so it does not find its own through the structure, its occupants or its wiring. It does this with three components in series: an air-termination system that intercepts the strike, down conductors that carry the current down the outside of the structure, and an earth-termination system that disperses it safely into the ground.
The internal LPS stops dangerous sparking inside. When a huge current flows down the external system, it raises the voltage of everything connected to it and can flash over to nearby metalwork or services, a real fire and shock hazard. The internal LPS prevents this in two ways: equipotential bonding, which ties the LPS, structural metalwork, pipes and incoming services together so they rise and fall in voltage together rather than sparking between each other, and a maintained separation distance, which keeps the LPS far enough from internal conductors that a spark cannot bridge the gap.
The components of an LPS
An LPS is built from a small number of well-defined parts. The first three form the external system that handles the strike; the rest protect the systems inside.
Air-termination system
What the strike actually hits: rods (finials), a mesh over the roof, or catenary wires above the structure, positioned so that lightning strikes them rather than the building. Placement is verified with methods such as the rolling sphere and protection angle. Read about air-termination methods.
Down conductors
The path that carries the captured current from the air termination down to earth. Several are spread around the structure so the current divides between them, which lowers the voltage on each and reduces the sparking hazard. Natural conductors such as steel reinforcement can serve this role.
Earth-termination system
The electrodes that disperse the current into the soil: a ring earth, rods or foundation earth. A low, stable earth resistance is what lets the current dissipate without raising ground potential dangerously. Read about earthing for lightning protection.
Equipotential bonding
Bonds the LPS to structural metalwork, pipework and incoming services, directly or through surge protective devices, so everything sits at the same potential during a strike and cannot spark across to internal parts. With the separation distance, it is the core of the internal LPS.
Surge protection (SPDs)
A strike radiates a lightning electromagnetic impulse (LEMP) that induces surges on internal wiring even without a direct hit. Coordinated surge protective devices (SPDs), with shielding and bonding, form the protection measures that keep those surges away from sensitive equipment.
Zoning (LPZ)
The interior is divided into lightning protection zones, from the exposed outside in to the most protected core, with SPDs and shielding at each boundary stepping the threat down. The zone concept is how surge protection is coordinated across a building. Read about LPZ zoning.
How lightning protection system components are specified
Knowing the six parts above is not the same as being able to specify them. IEC 62305-3:2024 (Ed.3) gives clause 5.5 to the components themselves, and the requirement there is stricter than most specifications assume. It names the parts one by one: conductors and air-termination rods, earth electrodes and their seals, the inspection houses over them, connection components, conductor fasteners, isolating spark gaps, earthing enhancing compounds, lightning strike event counters, and the components used in isolated systems. Every one of them has to take the electromagnetic forces a lightning current brings, and the stresses the design expects, undamaged. The standard says how that is proved: use components tested successfully against whichever part of the IEC 62561 series applies (5.5.1).
That single sentence is what separates a compliant LPS from an assembly of parts that merely look right. A conductor of the correct material and cross-section, joined by a clamp that was never tested to IEC 62561, is not a compliant system. The same clause pins the rest of the chain. Components are made from one of the materials Table 6 lists, which covers copper, hot galvanized steel, steel with electro-deposited copper, stainless steel, aluminium and lead. Another material is allowed where it matches those on mechanical strength, electrical performance and resistance to corrosion. A conductor fastener has to meet IEC 62561-4 (5.5.2). An insulating part, a stand-off or an insulated down conductor, has to meet IEC TS 62561-8 (5.5.4).
Connections carry a requirement that depends on the class, which is easy to miss when ordering. The number of connections along a conductor shall be kept to a minimum, and connection components are selected by their tested class under IEC 62561-1: class H for LPS class I and II, and class N for LPS class III and IV (5.5.3). So the class the risk assessment arrived at does not only set the geometry of the system, it reaches all the way down to which clamp is acceptable on the shelf.
Where each LPS component is specified
Each part of an LPS has a clause that says where it goes, a product standard the part itself must pass, and, for conductors and electrodes, a table of minimum sizes. This is the map of IEC 62305-3:2024 (Ed.3) by component.
| Component | Where it is specified | What the part must meet | Sizes and values |
|---|---|---|---|
| Air-termination system | Clause 5.2, placed by the rolling sphere, mesh or protection angle method (5.2.2) | IEC 62561-2 for rods and conductors (5.6.2) | Minimum cross-sections in Table 7 |
| Down-conductor system | Clause 5.3, with test joints at 5.3.6 | IEC 62561-2 for conductors (5.6.2), and IEC 62561-4 for the fasteners that hold them (5.5.2) | Minimum cross-sections in Table 7 |
| Earth-termination system | Clause 5.4, as a Type A or Type B arrangement (5.4.2.2, 5.4.2.3) | IEC 62561-2 for electrodes (5.6.2), and IEC 62561-7 where an earthing enhancing compound is used (5.4.1 NOTE 1) | Minimum electrode dimensions in Table 8 |
| Connections | Clause 5.5.3, with as few joints as possible | IEC 62561-1: class H for LPS class I and II, class N for class III and IV | - |
| Insulating stand-offs and insulated down conductors | Clause 5.5.4 | IEC TS 62561-8 | - |
| Equipotential bonding | Clause 6.2, for metal installations, external conductive parts, internal systems and incoming lines | IEC 62561-3 for any isolating spark gap that makes the bond in place of a direct connection (6.2.2) | - |
| Separation distance | Clause 6.3, a general and a simplified approach | - | Coefficients ki, km and kc from Tables 11, 12 and 13 |
| Surge protective devices | IEC 62305-4:2024, at each lightning protection zone boundary | The IEC 61643 series, as IEC 62305-2:2024 (Ed.3) clause 5.3 points out | - |
Each row is our summary of the clause cited, not the standard's wording. How to work out the separation distance on a real building is in separation distance calculation; the order in which the parts are designed is in lightning protection system design.
The class of LPS sizes every component
IEC 62305 builds an LPS to one of four classes, I to IV, each matched to a lightning protection level. The class is not a separate component. It is the setting that sizes the components above: the rolling sphere radius and mesh used to place the air termination, the spacing of the down conductors, and, as the table shows, which connection components are acceptable. The class is chosen by the Part 2 risk assessment, not by habit, and the order in which it is fixed and then applied is covered step by step in lightning protection system design.
These four classes belong to IEC 62305. NFPA 780-2026 uses Class I and Class II for something else: material sizes chosen by the height of the structure, Class I up to 75 ft (23 m) and the heavier Class II above it (Sections 4.1.1.1.1 and 4.1.1.1.2). AS 1768:2021 keeps four levels, LPL I to IV, set by its Section 2 risk assessment, each with its own interception efficiency (Table 3.1).
The lightning protection system in NFPA 780 and AS 1768
All three standards describe the same physical system. Each names the parts in its own words, places them by its own rules and decides the need for protection its own way, so a design follows one standard in full and never borrows a value from another.
| Job in the system | IEC 62305-3:2024 | NFPA 780-2026 | AS 1768:2021 |
|---|---|---|---|
| Takes the strike | Air-termination system (clause 5.2) | Strike termination devices: air terminals, masts, overhead ground wires, and metal parts whose thickness reaches 3/16 in (4.8 mm) (3.3.42, 4.5.1.1, 4.5.1.4) | Air terminals: an upright rod, a horizontal conductor raised above the roof, or a natural component such as a metal roof (Clause 3.2.1) |
| Carries the current down | Down-conductor system (clause 5.3) | Down conductors, the main conductors from the roof conductors to the grounding electrodes (3.3.9.3, 4.8) | Downconductors, dedicated or natural (Clauses 3.3.1, 3.3.2) |
| Passes it into the soil | Earth-termination system (clause 5.4) | Grounding electrodes: rods, concrete-encased electrodes, ground rings and others (4.12) | Earth termination network (Clause 3.5) |
| Stops sparking inside | Equipotential bonding and separation distance (clauses 6.2, 6.3) | Common bonding of all grounded systems near the base, and bonding of metal bodies (4.13, 4.15) | Equipotential bonding, or isolation by a separation distance (Clauses 3.6.1 to 3.6.3) |
| Protects the services | Coordinated SPDs (IEC 62305-4) | SPDs at every power service, and listed surge protectors on signal, data and communication lines (4.19.1, 4.19.2.1) | SPDs, required where the risk assessment calls for them and wherever direct strike protection is fitted (Clause 4.2.1) |
| Decides whether one is needed | The Part 2 risk assessment | An adopting code, the authority having jurisdiction or an insurer; the Annex L risk assessment is advisory (L.1, L.1.1.1) | The Section 2 risk assessment; direct strike protection must then be provided (Clause 3.1) |
What the US standard sets
No protection levels. The material class follows height (4.1.1.1.1, 4.1.1.1.2): a solid copper air terminal is 3/8 in (9.5 mm) in Class I and 1/2 in (12.7 mm) in Class II. The zone of protection comes from the roof placement rules, the angle method on multiple-level roofs up to 50 ft (15 m), or a rolling sphere of no more than 150 ft (45 m) (4.7.1, 4.7.2.1, 4.7.3.1.4). Flammable vapor structures, explosives and watercraft use 100 ft (30 m) (7.3.2, 8.2.1, 10.3.1.1). Air terminal tips stand at least 10 in (254 mm) above what they protect, within 24 in (600 mm) of corners, and no more than 20 ft (6 m) apart along edges, or 25 ft (7.6 m) for terminals 24 in (600 mm) or taller (4.5.2.1, 4.6.2.1 to 4.6.2.3).
Conductors, grounding and surges
Every structure gets at least two down conductors, and one for each 100 ft (30 m) of perimeter once the perimeter passes 250 ft (76 m) (4.8.10, 4.8.10.1). Ground rods are at least 8 ft (2.4 m) long and 1/2 in (12.7 mm) across (4.12.2.1), and the piping or rods of other services never stand in for them (4.12.1.3). Grounded systems are tied together near the base, no more than 12 ft (3.6 m) from it measured vertically (4.13.1). SPDs go at every power service (4.19.2.1). Inspection or testing is yearly unless the authority sets another interval (1.7).
What the Australian standard sets
The Section 2 risk assessment sets the protection level, and the level sets the geometry. Placement is by the rolling sphere alone (Clause 3.2.3), with a radius that shrinks as the level gets stricter and twice that radius over large flat surfaces (Table D.1). Terminals go on points and corners first, the standard sphere then checks the edges and the doubled sphere the flat areas (Clause D.3.2). A vertical rod is at least 500 mm long and stands no further back from the edge it protects than half its height (Clause 3.2.2.2).
Downconductors, earthing and sizes
Air terminals, downconductors and earth electrodes need a section of at least 35 mm² (Table 3.3). Downconductors run around the perimeter no more than 20 m apart, with at least two on any LPS (Clause 3.3.2). The earth termination network should measure 10 ohms or less before other services are bonded to it (Clause 3.5.3). Structures taller than 60 m also need side strike protection on their upper faces (Clause 3.2.4). Inspection is recommended at least every two years (Clause 5.4.4).
Both standards are sold by their publishers, NFPA and Standards Australia, and you need the
purchased text to design or certify a system. For the detail, read
NFPA 780 air terminal spacing,
the NFPA 780 zone of protection,
NFPA 780 grounding and bonding,
NFPA 780 surge protection,
AS 1768 air terminal placement,
AS 1768 earthing and
AS 1768 surge protection. Whether a US building
must have a system at all is covered in
is lightning protection required by code
Do lightning protection systems really work?
Yes, to a stated limit, and the standards say what that limit is. A lightning rod, an air terminal in the standards' words, gives a strike that was going to reach the building a metal point to attach to. NFPA 780-2026 Annex B.3.2.2, which is informative, explains the model behind placement: as the downward leader nears the ground, an upward leader starts from the structure at the striking distance, and that distance grows with the peak current. A rod is only one part. The conductors carry the current down and the electrodes pass it into the soil, so a rod with no proper path to earth protects nothing.
No conventional system catches every strike, because weak strikes come closer before they attach. AS 1768:2021 Table 3.1 states the share each protection level is designed to intercept, highest at LPL I and lowest at LPL IV. NFPA 780-2026 ties its standard 150 ft (45 m) sphere to a typical peak current of 10 kA, and notes that this peak represents 91 percent of lightning events (B.3.2.2). Those figures assume a system built and kept to its standard, which is why inspection is part of the system.
Design, inspection & maintenance
An LPS protects nothing on paper. Once designed to the right class, it has to be installed correctly and then stay in that condition for the life of the structure. Lightning protection is exposed to weather, corrosion and mechanical damage, and buildings change. A new rooftop plant, an extension or a severed conductor can quietly undermine a system that passed on commissioning.
That is why each standard makes inspection part of owning an LPS. IEC 62305-3:2024 (Ed.3) clause D.7.2.2 bases the interval on the structure, its components and its surroundings, and offers a yearly visual check with a complete inspection every three years as one choice. NFPA 780-2026 Section 1.7 asks for inspection or testing every year, and AS 1768:2021 Clause 5.4.4 recommends an inspection at least every two years. What each visit checks and measures is set out in IEC 62305-3 inspection and testing and the NFPA 780 inspection checklist.
Conventional vs ESE air terminations
The components above make up a conventional system: passive air terminations placed by the rolling sphere, mesh and protection angle methods. Early streamer emission (ESE) terminals, which claim a larger protected volume from one mast, are covered by other national standards such as the French NF C 17-102, not by IEC 62305. NFPA 780-2026 Section 1.1.3 leaves them out as well, and AS 1768:2021 places any terminal by the same Section 3 rules as a plain rod (Clauses 1.1.2, 3.2.2.2). The detail is in ESE air terminals and IEC 62305.
Questions answered
What is a lightning protection system?
What are the main components of an LPS?
What are the classes of LPS (I to IV)?
Is a lightning protection system always required?
What is the difference between external and internal LPS?
How often must a lightning protection system be inspected?
Do lightning protection systems really work?
What is the best protection against lightning?
Which standard covers a lightning protection system in the US and Australia?
The tolerable risk in IEC 62305-2 is not a fixed constant.
Clause 7.3 NOTE 1 gives RT = 1 × 10⁻⁵ per year as a
representative value of tolerable risk and adds that another value may be set once
the case has been investigated in detail. The standard's introduction then lets national or local regulations fix
RT, the tolerable frequency of damage FT
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