Lightning Protection

A lightning protection system intercepts lightning strikes and conducts the current safely to earth, so it does not pass through the building fabric, start a fire or damage equipment. External protection comprises air terminals or a mesh of conductors on the roof, down conductors on the façade or within the structure, and an earth termination network. Internal protection comprises equipotential bonding of metal services and surge protection devices on power, data and communications lines.

Not every building needs a system; the decision comes from a risk assessment considering height, exposure, construction, contents, occupants and the consequence of a strike. Tall buildings, buildings on exposed sites, hazardous stores, heritage buildings, hospitals and buildings with sensitive electronics usually do.

Design follows a lightning protection level chosen from the risk assessment. Under IEC and BS EN 62305 there are four levels (I is the most demanding), each with its own rolling sphere radius (20, 30, 45 and 60 metres), mesh size and down conductor spacing. Natural components such as a continuous steel frame, reinforcing steel or a metal roof can form part of the system if they are electrically continuous and thick enough, which is common in modern framed buildings and must be confirmed rather than assumed.

What shortens life:

• Roof works that detach conductors and do not reinstate them.
• New rooftop plant, solar arrays and antennas added without bonding or coverage.
• Copper theft of down conductors and earth tapes.
• Dissimilar metals: aluminium against copper or lead, causing corrosion at joints.
• Excavation that damages earth electrodes.

Loss of continuity

Conductors detach from their fixings, are cut during roof works, or are stolen. A break in the path means a strike looks for another way to earth: through the fabric, services or people.

Rising earth resistance

Earth electrodes corrode, soil dries, and connections loosen. Higher resistance means higher voltages during a strike and a greater chance of side flashing to services.

Coverage gaps

New plant, solar arrays, antennas, telecommunications masts and roof extensions sit outside the original protected zone or are left unbonded.

Bonding failures

Metal pipes, cable trays, handrails and plant that are not bonded can flash over to the protection system or to each other, causing fire or damage.

Surge protection exhaustion

Surge protection devices sacrifice themselves to protect equipment; after enough surges they no longer protect, often without obvious indication unless status indicators are checked.

Side flashing and touch voltages

Where metal services, plant or people are too close to a down conductor, the strike current can jump across the gap (side flashing). Near down conductors at ground level, people can be exposed to dangerous touch and step voltages; insulation, barriers or bonding control this.

Unverified natural components

Systems that rely on the steel frame or reinforcement as down conductors depend on continuity that was meant to be confirmed at construction. Later alterations, cut reinforcement and replaced roof sheeting can break that continuity without anyone noticing.

On the roof and façade

• Conductors loose, detached, cut or missing; fixings broken.
• Plant, solar and antennas without bonding connections.
• Corrosion at joints, especially between dissimilar metals.
• Test joints at the base of down conductors missing, damaged or painted over.
• Down conductors stolen at low level.

In the records

• Design, risk assessment and drawings.
• Inspection and test reports with earth resistance readings.
• Records of roof works and plant additions.
• Surge protection device status checks.

• Burn marks or melted fixings near air terminals after storms.
• Equipment failures after storms.

• Air terminals bent or missing after roof works.

After a strike, damage tells you where the current went: burns at joints and fixings point to poor connections; damage to equipment inside points to missing bonding or surge protection; damage to masonry points to side flashing or a broken conductor.

Findings are graded by what they demand: safety (can hurt someone now), failure (failed and damaging the building), condition (distress present and progressing), lifecycle (renewal due on age and exposure), deadline (a regulator or ordinance sets the date), check (investigate before sizing works) and nil (cosmetic or stable).

A lightning protection specialist or electrical engineer.

• Risk assessment to confirm whether protection is required and to what level.
• Visual inspection of air terminations, conductors, fixings, joints, bonding and test points.
• Continuity testing of conductors and bonds.
• Earth resistance testing of each electrode and the whole network.
• Coverage check of new plant, solar and antennas against the design.
• Surge protection review: devices present, status, coordination.

The report should give the system status, test readings against previous results, gaps, and works needed.

Inspection intervals under BS EN 62305 depend on the protection level: for levels I and II, a visual inspection every year and a complete inspection every two years; for levels III and IV, every two and four years. Critical structures such as those with explosive or flammable contents are inspected more often. Earth resistance is measured by fall-of-potential or clamp methods and compared with previous readings rather than judged alone.

• Reinstate and refix conductors; replace stolen sections with less attractive materials or concealed routes.
• Bond new plant, solar arrays and antennas.
• Extend coverage to new roof elements.
• Earth improvement: additional or replacement electrodes.
• Surge protection: replace exhausted devices and coordinate across boards and data entries.
• Redesign of ESE-based systems to a recognised standard where risk requires.
• Coordinate with re-roofing so the system is reinstated and tested.

Interactions: lightning protection must be bonded to new solar arrays, plant and antennas, coordinated with surge protection at the main switchboard, and reinstated after every re-roofing; heritage buildings may need conductor routes approved.

• Test joints reinstated at the base of every down conductor so future testing is possible.

Inspection and testing are recurring lump sums. Repairs are itemised by length of conductor or per bond. Earth improvements are per electrode. Full replacement is a lump sum, often carried with re-roofing. Surge protection is per device.

Testing and safety rectification are code compliance; repairs are repairs and maintenance; replacement is lifecycle.

Theft-prone sites may justify concealed or less valuable conductor materials despite higher installation cost. Inspections are best combined with roof access for other work.

• Australia. AS/NZS 1768 sets lightning protection, including risk assessment, design and inspection; surge protection follows AS/NZS 1768 and AS/NZS 3000.
• United Kingdom. BS EN 62305 sets risk assessment, design and inspection, with visual inspection and full testing at intervals set by the protection level (more often for higher levels); BS 7430 covers earthing.
• United States. NFPA 780 sets installation requirements; UL 96A covers installation and certification; NFPA 70 covers surge protection devices.

Insurers in all three jurisdictions may require lightning protection for high-risk buildings and evidence of inspection. Heritage buildings often have historic systems that need repair rather than replacement, with routes agreed with heritage authorities.

Explosives and flammable stores carry stricter protection and inspection requirements in all three jurisdictions under their hazardous materials rules.

• Risk assessment and design drawings.
• Inspection and test reports with earth resistance readings.
• Records of roof works and plant additions.
• Surge protection device schedule.

• Insurer requirements and inspection records.
• Records of strikes and storm damage.
• Heritage constraints on conductor routes.

• Records of plant, antennas and solar added to the roof since the last inspection.