Periodic inspection of a lightning protection system (LPS) — IEC/EN 62305-3 test intervals

The lightning protection risk-analysis guide, the separation-distance guide and the LPZ zoning guide cover how a lightning protection system (LPS) is designed. This article covers what happens after installation: how and how often an already installed LPS must be periodically inspected, per IEC/EN 62305-3 Annex E — a distinct inspection regime that runs alongside, and does not replace, the ordinary NEN 3140 inspection of the electrical installation itself.

Three inspection types

IEC/EN 62305-3 distinguishes, similar in structure to the periodic inspection regime for explosion-protected equipment, three types of LPS inspection:

Visual inspection — checks for obvious damage, corrosion, loose or disconnected joints, vegetation growth interfering with air terminals, and — critically — new equipment added to the structure (rooftop PV, HVAC units, antennas) that has not yet been bonded into the air-termination system.
Complete inspection — includes the visual inspection, plus continuity and resistance measurement of down conductors and the earth-termination system, physical inspection of joints and connections, and verification of surge protective device (SPD) condition.
Critical inspection — a complete inspection carried out specifically after a structural modification or extension, after a known direct lightning strike, or after any repair to the LPS — not tied to the normal calendar interval.

Indicative inspection intervals

Note: the exact interval follows from the structure's Lightning Protection Level (LPL I–IV, determined in the risk analysis — see the risk-analysis guide) and the criticality of the structure's contents; the table below illustrates the typical pattern rather than a single universal number.

Lightning protection level / criticality	Visual inspection	Complete inspection
LPL I/II, or structures with a critical systems risk (e.g. explosive or highly hazardous content)	annually	every 2 years (critical systems: annually)
LPL III/IV, ordinary structures	every 2 years	every 4 years

SPD status indicators are typically checked on a shorter, often annual, cycle regardless of the overall LPS interval, since a failed SPD otherwise goes unnoticed until the next full inspection.

Earth-termination system: continuity matters more than a single resistance value

A complete inspection includes measuring the resistance and continuity of the earth-termination system, typically at each down-conductor test joint. Unlike some other earthing contexts, IEC/EN 62305-3 does not prescribe one single universal maximum resistance value that every LPS earth-termination system must meet — soil conditions and electrode configuration vary too widely for that. What the standard treats as more decisive is continuity and equipotential bonding: confirming that every down conductor is actually electrically connected to the earth electrode with low, consistent resistance, rather than chasing one fixed target number in isolation.

A separate regime, not a substitute for NEN 3140

A regular NEN 3140 inspection assesses the general electrical safety of the installation and work equipment. The IEC/EN 62305-3 inspection is an additional, structurally distinct regime specifically for the lightning protection system: it verifies that the LPS itself — air terminals, down conductors, earth-termination system, bonding of later rooftop additions, and SPDs — is still intact and effective. This mirrors the same relationship the ATEX periodic inspection guide describes between the ordinary electrical inspection and the explosion-protection inspection regime: both run in parallel, and neither replaces the other.

Relationship to SPDs

Surge protective devices installed as part of the coordinated overvoltage protection covered in the SPD energy coordination guide are also physically part of many LPS installations (particularly Type 1 SPDs at the origin of the installation). Their periodic functional check — status indicator inspection, and replacement or testing per the manufacturer's instructions — is normally scheduled alongside the LPS inspection, since a failed SPD compromises the coordinated overvoltage protection the LPS design relied on.

Practical relevance

For a building or installation with a designed LPS, the inspection schedule should explicitly record the inspection type (visual/complete/ critical) and interval per the structure's own LPL and criticality — not a generic, one-size-fits-all interval copied from another site — and must be updated whenever new rooftop equipment is added, since that equipment needs to be bonded into the air-termination system at the time of installation, not discovered unbonded at the next scheduled inspection.

Common mistakes

Assuming the regular NEN 3140 electrical inspection also covers the LPS — it does not; a separate schedule under IEC/EN 62305-3 is required.
Leaving later rooftop additions (PV arrays, HVAC units, antennas) unbonded to the air-termination system — a common real-world gap, because the work is often done by a different trade than the one that installed the original LPS.
Fixating on a single target resistance value for the earth-termination system, rather than verifying continuity and equipotential bonding, which the standard treats as the more decisive criterion.
Skipping the critical inspection after a known direct lightning strike on the assumption that "no visible damage" is sufficient — internal damage to down conductors, joints or bonding connections is not always visible from a simple walk-around.