By Getting lightning arrester design for buildings right is not about bolting a rod to the roof — it is a system that intercepts a strike, carries the current safely down the outside of the structure, and disperses it into the earth without letting dangerous voltages appear inside. Done to standard, it protects the building, the people in it, and the electronics connected to its wiring. This guide walks through the design in the order a real project follows, referenced to IS/IEC 62305 and India’s National Building Code (NBC 2016, Part 8).
Step 1 — Risk assessment comes first
Before choosing any hardware, IS/IEC 62305-2 asks you to assess risk. The assessment weighs the building’s height and footprint, its location and the local thunderstorm/flash density, the type of construction, and the value of what is inside — people, equipment, and the consequences of a fire or data loss. The output is whether protection is needed and, if so, the Lightning Protection Level (LPL I–IV). The level then sets the mesh size, rod spacing and down-conductor spacing for the rest of the design. Skipping this step is the most common design mistake — it leads to systems that are either unsafe or needlessly expensive.
Step 2 — Air termination (intercepting the strike)
The air-termination system is what the lightning attaches to. There are three recognised approaches, and IS/IEC 62305-3 lets you combine them:
- Rods (Franklin rods) — vertical air terminals at high points and corners, sized and spaced to the protection level.
- Mesh method — a conductor grid over the roof, with mesh dimensions set by the LPL (finer mesh for higher protection).
- Catenary/wire — spanned conductors over the area to be protected.
The protected zone of each rod is verified with the rolling-sphere method — imagine a sphere (radius set by the LPL) rolled over the building; anything it cannot touch is protected. For large, open or architecturally complex roofs, an ESE-type air terminal can cover a wider radius from a single mast, reducing the number of rods. Note that ESE is applied under separate national practice and is debated against 62305 in some jurisdictions — specify it transparently and keep conventional 62305 air termination as the reference design.
Step 3 — Down conductors (getting current to ground)
Down conductors carry the strike current from the air termination to earth. Design rules that matter: run at least two down conductors and distribute them around the perimeter; keep them as straight and vertical as possible with no sharp bends (a lightning current will jump a tight loop); and space them according to the protection level. Natural conductors — steel reinforcement and metal façades — can be used where they are electrically continuous, which is often the most economical route in modern RCC buildings. Every down conductor gets a test/disconnecting link above its earth electrode so the earthing can be measured independently.
Step 4 — Earthing (dispersing the energy)
The earthing system is where the strike energy finally goes, and it is the part most often under-built. IS/IEC 62305-3 favours a Type B ring earth electrode around the building, bonded to the foundation earth where possible, with a target earth resistance typically 10 ohms or lower. Vertical copper bonded rods and, in high-resistivity soil, a low-resistance backfill improve dispersion. Crucially, the lightning-protection earth must be bonded to the building’s electrical earth to prevent dangerous potential differences — a single, equipotential earthing system, not two isolated ones. Permanent connections in the grid are best made by exothermic welding.
Step 5 — Surge protection and bonding (protecting what’s inside)
The external system protects the structure. To protect equipment, IS/IEC 62305-4 requires an internal Lightning Protection Zone (LPZ) concept: bond all incoming metallic services (power, data, water, gas) at entry, and install coordinated surge protection devices (SPDs) — Type 1 at the main incomer, Type 2 at sub-boards, Type 3 near sensitive electronics. Without SPDs, the surge that couples into the wiring during a nearby strike will still destroy connected equipment even when the building itself is protected.
Step 6 — Testing, documentation and maintenance
A design is only complete when it is verified. Measure earth resistance at each test link and record it; check continuity of down conductors; and keep an as-built drawing with the LPL, rolling-sphere radius and component list. IS/IEC 62305 expects periodic inspection — typically annually for critical sites and after any major strike — because clamps loosen and soil resistivity changes with the seasons.
For the full engineering detail behind each step, see our detailed lightning protection system design guide and the lightning protection system overview. For houses specifically, see the lightning arrester for home guide. Ashlok’s lightning protection systems and conventional lightning protection ranges cover the hardware for every step.
Frequently asked questions
Which standard governs lightning arrester design for buildings in India?
IS/IEC 62305 (Parts 1–4) is the core standard, and the National Building Code of India (NBC 2016, Part 8) references it for building works. Together they cover risk assessment, air termination, down conductors, earthing and surge protection.
How many down conductors does a building need?
At least two, distributed around the perimeter, with spacing set by the protection level (LPL I–IV). Taller and higher-risk buildings need more, closer-spaced down conductors.
What earth resistance should a lightning protection system have?
A common target is 10 ohms or lower, achieved with a ring/Type B electrode, copper bonded rods and, in poor soil, a low-resistance backfill. The lightning earth must be bonded to the building’s electrical earth.
Is an ESE lightning arrester the same as a Franklin rod design?
No. A Franklin/conventional design uses rods and mesh verified by the rolling-sphere method under IEC 62305. An ESE terminal claims a wider protective radius from a single mast and is applied under separate national practice; specify it transparently alongside a conventional reference design.
Do I still need surge protection if the building has a lightning rod?
Yes. The external system protects the structure; coordinated SPDs (Type 1/2/3) protect the equipment inside from the surge that couples into the wiring. IS/IEC 62305-4 treats both as parts of one system.
Ashlok designs and manufactures complete lightning-protection and earthing systems to IS/IEC 62305, since 1999. Talk to Ashlok about your building →