Rolling Sphere Method (RSM) Modelling

A lightning protection system is only as effective as its coverage. Gaps in air termination placement aren't visible from a drawing review or a site walk, they exist in three dimensions, defined by facility geometry and the physics of lightning attachment.

Aetheric uses 3D RSM modelling to identify unprotected zones, optimise air termination placement, and validate compliance with your target lightning protection level. Engineering certainty, not assumed coverage.

The Rolling Sphere Method is the internationally recognised technique for verifying lightning protection coverage, illustrated above. Any point the sphere contacts before reaching a protection conductor represents a potential strike point requiring additional protection.

The sphere radius is determined by the lightning protection level (LPL) defined in IEC 62305 and AS/NZS 1768:2021. Higher protection levels use smaller radii, requiring more comprehensive air termination systems to eliminate coverage gaps:

LPL selection is driven by risk assessment results, regulatory requirements, and operational criticality. Where appropriate, we model coverage at multiple LPL options to support informed cost/effectiveness decisions.

Modelling runs in XGSLab's Lightning module integrated with CAD-based geometry tools.

1. Geometry Import

Facility 3D geometry imports from AutoCAD, Revit, or equivalent, building volumes, rooftop equipment, elevated structures, and existing protection conductors all represented accurately, not approximated.

2. Protection Zone Analysis

The sphere is applied at the specified LPL radius across the facility envelope. Every contact point that doesn't first reach a protection conductor is flagged as an unprotected zone, visualised in 3D coverage maps with the geometry creating each gap.

3. Iterative Optimisation

Air termination placement is adjusted (added, relocated, extended) and re-run until coverage is complete, minimising additional hardware while eliminating gaps.

4. Multi-Level Analysis

Where different LPLs apply across zones (e.g., LPL I for a control room, LPL III for a warehouse), each zone is modelled independently and coverage transitions verified between them.

Prescriptive approaches work for simple rectangular structures. Real facilities rarely are. RSM modelling earns its keep on:

• Multi-level rooftops, stepped roof profiles where lower levels may be shielded by higher structures, or may not be
• Rooftop equipment, HVAC units, antennas, satellite dishes, and exhaust stacks that create shadow zones and may themselves require protection
• Architectural features, parapets, overhangs, canopies, and facade elements that complicate conductor routing
• Adjacent structures, neighbouring buildings or equipment that may provide incidental shielding, or may create new exposure paths
• Expansion areas, future building phases or planned equipment additions that should be considered in current protection design
• Restricted areas, zones where conductor placement is constrained by aesthetics, operational access, or hazardous area classification

Planning a New System or Verifying an Existing One?

RSM modelling gives you the engineering confidence that your protection design works in three dimensions, not just on paper.

RSM modelling supports protection design across all sectors where facility geometry creates coverage complexity:

Every RSM modelling engagement delivers:

RSM modelling typically sits within a broader protection engineering workflow. Depending on where you are in your project, these services connect directly:

• Risk Assessment Studies, if your facility's lightning protection level hasn't been formally determined, a risk assessment establishes the required LPL before RSM modelling begins
• Lightning Protection Systems, RSM results feed directly into detailed protection system design, including air termination, down conductors, and SPD coordination
• Design Services, when RSM analysis is part of a larger design package, our team delivers construction-ready documentation integrating all protection elements
• Ground/Earthing Testing, protection system performance depends on effective earthing; field testing validates that the earthing system supports the protection design
• Lightning Resiliency Planning, for organisations managing multiple facilities, RSM analysis across the portfolio informs enterprise-level protection strategy