What is NFC 17-102?
NFC 17-102 is the standard published by AFNOR (the French standards body) that governs the design, testing, installation and maintenance of ESE (Early Streamer Emission) lightning protection systems. The current edition is NFC 17-102:2011.
Although it originates in France, NFC 17-102 has been adopted as the primary ESE standard across much of Europe, the Middle East, Asia and Latin America. It provides the only internationally recognised methodology for:
- Measuring and certifying the ΔT advance time of an ESE lightning rod
- Calculating the protection radius (Rp) based on ΔT, installation height and protection level
- Conducting the risk assessment that determines which protection level a structure requires
- Specifying installation requirements for the complete LPS
The ΔT Test — How ESE Lightning Rods Are Certified
The core of NFC 17-102 is Annex C, which defines the comparative test procedure for measuring ΔT. In this test, an ESE lightning rod and a simple reference rod are subjected to identical simulated lightning conditions in a high-voltage laboratory. The time difference between the upward leader initiation of the ESE and the reference rod is measured — this is ΔT.
For a device to be certified as an ESE under NFC 17-102, its ΔT must be:
- Greater than 10 µs (minimum to qualify as ESE)
- Not greater than 60 µs (maximum recognised by the standard)
A device claiming a ΔT outside this range — whether below 10µs or above 60µs — is not an ESE per NFC 17-102 and its claimed protection radius cannot be calculated using the standard's formula. ORBITAL lightning rods are independently tested and certified with confirmed ΔT values within the 10–60µs range.
Important: Any manufacturer claiming a ΔT value above 60µs is not compliant with NFC 17-102. The standard explicitly caps the maximum recognisable advance time at 60µs. Claims of 100µs, 120µs or higher are not recognised under the standard and have no basis for calculating a certified protection radius.
Protection Radius Calculation
The NFC 17-102 protection radius formula is: Rp = √[h(2r − h) + ΔT(2r + ΔT)]
Where h is the installation height of the ESE tip above the protected structure (minimum 2m), r is the standard radius for the required protection level (20/30/45/60m for Level IV/III/II/I), and ΔT is the certified advance time in microseconds.
This formula demonstrates two important design principles. First, increasing installation height h has a significant multiplying effect on Rp — a 2m increase in mast height can increase the protection radius by 8–15m. Second, ΔT and h interact: the same ΔT produces a larger Rp benefit at greater installation heights. ORBITAL recommends a minimum mast height of 4–6m above the highest structural point for most installations. See the full protection radius table for calculated values across common configurations.
Risk Assessment Under NFC 17-102
NFC 17-102 requires a formal risk assessment before specifying any ESE installation. The assessment compares Nd (expected annual strike frequency, based on the regional lightning density Ng, the structure's equivalent collection area Ae, and its location factor C1) against Nc (the tolerable strike frequency, based on the structure type, contents and occupancy).
If Nd ≤ Nc, no lightning protection is required. If Nd > Nc, the required protection efficiency E = 1 − (Nc/Nd) determines the protection level. Use the ORBITAL NFC 17-102 Risk Calculator to run this assessment for your structure.
Maintenance Requirements
NFC 17-102 mandates periodic inspection of ESE installations. The standard requires a verification after every recorded lightning strike, after any structural modifications to the protected building, and at regular intervals depending on the protection level. Inspection must include measurement of the earthing resistance, verification of electrical continuity of all conductors, and functional testing of the ESE lightning rod using a certified test unit such as the ORBITAL ORB-ONE ESE Test Unit.