IEC 62305 risk assessment, computed clause by clause
Lumex runs the complete IEC 62305-2:2024 procedure on Voltrace™, its risk engine, the current third edition, not a simplified estimator, so every number traces back to the clause and coefficient you can defend.
One risk R, plus a frequency of damage F
IEC 62305-2:2024 combines injury to people and loss from fire into a single risk R, judged against the tolerable risk RT, for which clause 7.3 NOTE 1 gives 10⁻⁵/yr as a representative value and your jurisdiction may set its own. Alongside it sits a separate frequency of damage F for the availability of internal electrical and electronic systems, judged against its own tolerable frequency of damage FT. Every verdict traces back to the clause behind it.
R · vs RT
The risk of injury to people
Touch and step voltages, plus fire after a strike. The 2024 edition combines injury to people and loss from fire into this single risk R, held to the strictest tolerable line.
F · vs FT
Frequency of damage F
How often a strike disrupts the availability of internal electrical and electronic systems, judged against a tolerable frequency of damage FT. The concern for data centres and control rooms.
NSG · strike-point density
Ground strike-point density
The 2024 edition drives the dangerous-event rate from a ground strike-point density NSG, replacing the older flash density NG, because one flash can strike the ground at several points.
TWS · IEC 62793
Thunderstorm warning systems
The 2024 edition recognises thunderstorm warning systems, per IEC 62793, as a measure that lowers the probability of harm to people during the window of greatest exposure.
Nine risk components
Every risk is the sum of components; each component = dangerous-event rate (N) × probability of damage (P) × loss factor (L).
| Comp. | Source & cause | Belongs to |
|---|---|---|
| RAT | Direct flash to the structure causing touch and step voltages inside it, and outside within 3 m of a down conductor | R |
| RAD | Direct flash to a person exposed on the structure | R |
| RB | Direct flash to the structure causing dangerous sparking and fire | R |
| RC | Direct flash to the structure causing internal system failure (LEMP) | R, F |
| RM | Nearby flash inducing failure of internal systems | R, F |
| RU | Flash to a connected line causing touch voltage indoors | R |
| RV | Flash to a connected line causing fire or explosion via the service | R |
| RW | Flash to a connected line causing internal system failure | R, F |
| RZ | Flash near a connected line inducing internal system failure | R, F |
From flash density to a verdict you can defend
Every component follows the same chain. Lumex carries each named number through, so you can read the trace from the first input to the final pass or fail.
Collection area (Annex A)
How much ground around the building attracts a strike, from its length, width and height. Adjacent and line-attracted areas (Am, Al, Ai) follow the same annex.
Dangerous-event rate
How many strikes per year that area can expect. NSG is the local ground strike-point density (the 2024 edition's measure, in events / km² / yr, replacing the older flash density); CD is the location factor.
Probability of damage (Annex B)
How likely a strike is to actually cause damage. Protection measures lower P. An LPS of Class I drives PB to 0.02; a coordinated Type 1 SPD set drives PSPD to 0.01.
Loss factor (Annex C)
How much is lost if damage does happen. Fire-protection (rp), fire-risk (rf) and special-hazard (hz) factors scale the typical loss values.
Component and risk
Each component is N times P times L. Sum them into the risk R and compare it to RT; the frequency components sum into F and compare to FT, for a clear pass or fail.
The risk R fails. One upgrade makes it pass
A real data centre, assessed clause by clause. Same inputs, same maths Lumex runs on every project, with the verdict you can defend.
The building & inputs
Bhiwadi data centre
Illustrative example · Zone Z2 · Rajasthan
The verdict, traced
As built · Class III LPS
R = 2.4×10⁻⁵
exceeds RT 1.0×10⁻⁵
Fix: upgrade to LPS Class II, dropping PB to 0.05.
After fix · Class II LPS
R = 4.8×10⁻⁶
within RT 1.0×10⁻⁵
Every figure here is computed by Voltrace™, not estimated, straight from IEC 62305-2:2024. Run the same trace on your own building in minutes.
Get startedLumi speeds the routine. Voltrace still owns every number
You just saw that trace, computed clause by clause. Lumi works around Voltrace to cut the busywork, with the signing engineer in control at every step.
Risk-driver analysis
Reads the completed trace and shows which component drives each risk, so you know exactly where to act.
Drafted report narrative
Turns your computed figures into clear report prose you review, edit and approve before it is filed.
Ranked mitigation options
Suggests protection upgrades and ranks them by their effect on the risk R, with the maths shown for each.
Early fail flags
Flags risks likely to exceed RT as you enter inputs, long before you reach the final verdict.
Where Lumex fits the standard series
Lumex runs the IEC 62305-2 risk assessment and reports the protection level your design must meet. The Part 3 layout is yours to draw and a competent person's to sign. Final responsibility for every result rests with the signing engineer, and Lumex does not replace professional judgement or the published standard. Lumex is an independent product and is not affiliated with or endorsed by the IEC; the coefficient values shown here are illustrative, and the authoritative tables are defined in IEC 62305, available from the IEC.
General principles
Lightning parameters & damage model that underpin Lumex's terminology and LPL definitions.
Risk management
The full procedure Voltrace implements: the risk R and frequency of damage F, all nine components, every annex coefficient.
Physical damage & life
LPS classes and the §E.7 periodic-inspection report referenced by Lumex.
Electrical & electronic systems
SPD coordination and LEMP-protection factors feed the PSPD and PM inputs.
Why "on the 2024 third edition" matters
IEC 62305 was rewritten in 2024 for the first time in fourteen years. Most spreadsheets, templates and older tools still run the 2010 maths. Lumex is built on the published third edition (2024), adopted nationally across most of the world, so the report you file matches the standard an auditor cites today.
First edition
The four parts of IEC 62305 first brought lightning protection under one risk-based framework.
Second edition
A refined risk model, and the edition most legacy spreadsheets and Word templates still encode today.
Third edition
A full technical revision across all four parts, published in September and October 2024. The edition Lumex computes.
What the third edition changed. The 2024 revision moved to a ground strike-point density (NSG) in place of the older flash density, brought injury to people and loss from fire into a single combined risk view, added a frequency-of-damage measure for the availability of internal systems, and recognised thunderstorm warning systems (per IEC 62793) as a way to reduce risk. Lumex tracks these changes, so your assessment reflects current practice rather than the 2010 method.
Lumex computes the IEC 62305-2 method and shows the working. It does not certify a structure. You may not issue or submit a Lumex output until a competent person, qualified where the structure is located, has reviewed the inputs and the result and signed it.
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. Printed p.12 then lets national or local regulations fix RT, the tolerable frequency of damage FT, and the Annex A, B, C and E calculation rules and parameter values. Every Lumex assessment states the jurisdiction it was computed under and the values that applied.