In the field, the question comes up regularly: does this building need lightning protection, and if so, at what level? The rigorous answer requires a complete risk analysis according to IEC 62305-2 — a valuable but time-consuming approach, reserved for engineering firms. For installers and electricians working on standard structures, there is a simplified method perfectly suited: the FD C 17-108:2017, now integrated into LPS Manager.
What is FD C 17-108 and what is it used for?
The FD C 17-108 (AFNOR normative document, 2017) is a simplified method for determining the Lightning Protection Level (LPL) based on IEC 62305-2 principles. It was designed to:
- Allow rapid assessment of lightning risk on structures of standard complexity
- Be applicable directly in the field by a qualified installer or electrician
- Cover the vast majority of standard structures (ordinary fire risk, buildings outside ATEX, non-explosive)
FD C 17-108 simplifies IEC 62305-2 by reducing the number of parameters to be entered and by proposing fixed values for the least variable factors. It results in the determination of a Lightning Protection Level (LPL) from I to IV, which determines the characteristics of the protection system to be implemented.
Note: FD C 17-108 is not a complete risk analysis in the sense of IEC 62305-2. For ATEX structures, industrial facilities subject to environmental regulations, or structures with particular characteristics (risks to human life, irreplaceable cultural heritage), only a complete IEC 62305-2 analysis carried out by a competent engineering firm is acceptable.
The 4 lightning protection levels: what changes in practice
The LPL determined by the FD C 17-108 method directly determines the technical characteristics of the protection system:
- LPL I (maximum protection): reference lightning current 200 kA, reduced protection angle, fictitious sphere radius 20 m. Required for very high-risk structures.
- LPL II: reference current 150 kA, fictitious sphere radius 30 m.
- LPL III: reference current 100 kA, fictitious sphere radius 45 m. Most common level on standard industrial and tertiary buildings.
- LPL IV (minimum protection): reference current 100 kA, fictitious sphere radius 60 m. Low-exposure and low-consequence structures.
For an installer, the LPL determines the choice of PDA lightning rod model (initiation advance required to achieve the protection radius), the performance level of surge arresters (Iimp for Type 1) and the characteristics of conductors and earthing systems.
How LPS Manager integrates the FD C 17-108 method
LPS Manager has integrated the FD C 17-108 method directly into its web interface, making the LPL calculation accessible from any connected device — computer, tablet or smartphone.
Step 1: enter site characteristics
The installer enters the site data into LPS Manager:
- Geographic location: LPS Manager automatically retrieves the Nsg value (lightning density in air) via Météorage data for sites in France, and LPS France API data for other countries.
- Structure dimensions: length, width, height of the building
- Type of structure and environment: exposure (rural area, urban area, area with taller structures), roof type, presence of nearby structures
- Content type: standard equipment, flammable materials, people…
Step 2: automatic LPL calculation
LPS Manager automatically calculates the required Lightning Protection Level according to the FD C 17-108 method. The result is displayed clearly with intermediate values (impact frequency ND, tolerance frequency NT), allowing the installer to understand and validate the result.
Step 3: pre-selection of suitable equipment
Based on the calculated LPL, LPS Manager can guide the installer towards suitable LPS France equipment (Paraton@ir model, Type 1/Type 2 surge arrester level), and pre-fill the technical characteristics of the study file.
Step 4: generation of PDF report
Once the data is validated, LPS Manager generates a structured PDF report incorporating the results of the FD C 17-108 analysis, normative references, site characteristics and protection requirements. This document can be delivered directly to the client or included in the installation file.
Practical case: application to a logistics warehouse
Let’s take a concrete example: a logistics warehouse of 80 x 40 m, height 10 m, in a peri-urban area (Toulouse), containing standard goods (ordinary fire risk).
With LPS Manager and the FD C 17-108 method:
- Nsg automatically retrieved for Toulouse: ~2.5 arcs/km²/year (example value)
- Calculation of impact frequency ND: taking into account dimensions and environment
- Comparison with tolerance frequency NT according to content type and structure
- Result: LPL III required
This result directly guides the choice of a PDA with suitable initiation advance to cover the roof with the protection radius corresponding to LPL III, and Type 1+2 surge arresters at the head of the installation.
Why FD C 17-108 covers 90% of field cases
The simplified FD C 17-108 method is suitable for structures with ordinary fire risk, which is the vast majority of buildings that installers and electricians encounter in their daily activities:
- Industrial buildings and warehouses
- Offices and tertiary buildings
- Agricultural buildings
- Public reception establishments (ERP) of standard size
- Collective residential buildings
It is not applicable to ATEX structures, explosive storage facilities, sites with particular risks to people (hospitals, unique historical monuments) or complex industrial installations — for which only a complete IEC 62305-2 study is appropriate.
Conclusion: LPL in a few minutes in the field
Integrating the FD C 17-108 method into LPS Manager means giving every installer and electrician the ability to objectively determine the lightning protection level required for a building, directly from the field or from their office, in just a few minutes.
No need to wait for an engineering firm for standard structures: you have the results immediately, documented, normatively referenced, and ready to be included in the client file.
Discover LPS Manager Pro and access all calculation, report generation and client file management features at lpsmanager.io. Free trial available.
