Lightning Protection Inspection and Maintenance: Intervals, Checks, Records

When the system is inspected, and by whom

Clause 7 of DSTU EN 62305-3:2021 names four occasions (cl. 7.3): during construction, after installation, periodically, and after alterations or repairs or whenever it is known that lightning has struck the structure. Informative Annex E recommends inspecting the system during installation as well, particularly when components are fitted that will be concealed and become inaccessible for inspection; on a mast that is, for example, the electrode in the foundation. While there is a thunderstorm hazard, the system must not be inspected, tested or maintained (cl. 7.1).

Annex E recommends entrusting the inspection to a lightning protection specialist (cl. E.7.1). In practice the owner of the mast, or the organisation that operates it, orders the inspections; under the annex, the programmes of inspection and maintenance are approved by the competent authority, or by the designer or installer of the system, together with the owner.

Intervals under Annex E

The normative clause 7.3 gives no intervals and refers to Annex E: the interval depends on the nature of the structure, corrosion and the LPS class. Table E.2 gives the maximum intervals:

Source: DSTU EN 62305-3:2021, Annex E (informative), Table E.2: recommendations, not a legal requirement. Critical situations may include structures with sensitive internal systems, office and commercial buildings, and places where crowds gather. In Table E.2 the first column is headed “protection level”; under Table 1 of the standard, lightning protection levels (LPL) I–IV correspond to LPS classes I–IV, so “class” is used here.

A discrepancy in the annex, and special cases

The annex is inconsistent here: for classes III and IV the table permits a visual inspection every 2 years, while the text next to it recommends inspecting at least annually, and more often than the table says where the weather changes sharply or conditions are extreme. The annex does not say which of the two prevails, so it is safer to inspect the system visually every year.

The text suggests a full inspection with tests every 2–4 years, and every year in critical environmental conditions (the annex gives flexible bonding straps in areas with strong winds as an example). A full test every year may also be required by the client’s maintenance programme or the insurer. Where the competent authorities have special requirements, those apply instead of the table. The interval is also affected by the environment (more frequent inspections in a corrosive atmosphere), the materials and the soil condition.

Buildings and structures with an explosion risk are covered by the normative Annex D. There, electrical tests of the LPS are made every 12 (+2) months or at a separately determined interval (cl. D.6.5; that clause does not explain the +2). Surge protective devices (SPDs) are checked at intervals of not more than 12 months or whenever the LPS is electrically tested, and also after every suspected lightning strike (cl. D.6.7). Note a to Table E.2 of the informative Annex E calls a visual inspection every 6 months necessary for such structures; it recommends electrical tests once a year and accepts a 14–15-month cycle as an exception where earth resistance is measured in different seasons to capture seasonal variation. Whether your facility belongs here is for the design to decide.

What an inspection covers

Under Annex E an inspection covers a review of the documentation, a visual inspection, tests and an entry in the report. Among other things, the visual inspection verifies that:

• the design complies with the standard, and the system matches the design and is in good condition;
• there are no loose connections or breaks in conductors;
• there is no corrosion, especially at ground level;
• earth connections are intact, conductors are firmly fixed and the mechanical protection is in place;
• no additions or changes have been made to the structure that may call for additional protection;
• there are no signs of damage to SPDs or of blown fuses;
• the separation distance is observed.

Where the steel shaft itself serves as the down conductor, it makes sense to add the joints between its sections and its flanges to this list. The standard does not name the sections of a shaft separately, but it ties the use of a metal structure as a natural down conductor to reliable electrical continuity between its parts (cl. 5.3.5 a; connections, cl. 5.5.3). How the joints are to be checked is decided by the design.

Measurements: continuity and earth resistance

The tests under cl. E.7.2.4 are a continuity check (above all of the parts that cannot be inspected visually) and a measurement of the earth resistance. The results go into the report.

The resistance of each electrode is measured separately, with the test joint between the down conductor and the electrode open; where practicable, the resistance of the whole earthing system is measured as well. Under cl. 5.3.6 a test joint has to be fitted on every down conductor, except natural down conductors connected to foundation electrodes, and it must be openable only with a tool. For vertical rods and a ring electrode this is done in an inspection pit; where that is difficult, the annex recommends high-frequency or impulse measurements instead.

A low earthing resistance (up to 10 ohms at low frequency, where possible) is only recommended by the standard (cl. 5.4.1). If the resistance of the whole system, measured at a frequency other than the power frequency and its multiples, is below 10 ohms, the minimum electrode lengths of Figure 3 may be disregarded (cl. 5.4.2.1). If more is measured, the annex recommends checking the electrodes against Figure 3; for electrodes in rocky soil the requirements of cl. E.5.4.3.5 apply instead, and the 10-ohm requirement does not. If the earthing does not meet these requirements (electrodes per Figure 3, condition and continuity of conductors and joints), or this cannot be checked for lack of data, the annex considers it necessary to improve the earthing: add electrodes or build a new system. So the 10-ohm figure is not a verdict in itself, but neither is it a reason to do nothing.

Soil resistivity changes with the seasons, especially where temperature and precipitation vary widely, so the annex suggests assessing the resistivity profile with depth in different weather periods. A substantial change in earth resistance is a reason to look for the cause. If the resistance changes by more than the design provided for, and especially if it rises steadily from one inspection to the next, the annex recommends improving the earthing. How an earth electrode system is designed is covered in earthing of metal poles.

The inspection report and records

The annex suggests preparing LPS inspection instructions (test methods, how the results are recorded) and giving the inspector the design and the earlier reports. The report, in the annex’s view, needs the following information:

• the condition of the air termination conductors and other components of the air termination system;
• the level of corrosion and the state of corrosion protection;
• the security of fixings;
• the measured earth resistance;
• deviations from the requirements of the standard;
• changes and additions to the LPS and to the structure itself;
• the results of the tests.

Under cl. E.7.3.3 the maintenance records are kept together with the design of the LPS and the inspection reports.

Maintenance and repair

The components of the system typically lose their effectiveness over a few years through corrosion, weather damage, mechanical damage and lightning strikes (cl. E.7.3.1), so maintenance is needed even where corrosion protection was provided. According to the annex, the maintenance programme needs a checklist for comparing new results with earlier ones: inspection of conductors and components, continuity, earth resistance, SPDs, tightening of holders, and a check of the protection after changes to the structure (on a mast, for example, new antennas or cables).

According to the annex, repair, if it is needed, should be done at once, without waiting for the next cycle. Under cl. 7.4 all defects found are to be reported to the property owner and put right without delay.

The condition of the steel shaft itself (welds, flanges, anchors, coating) is assessed separately, in a technical inspection of steel structures. See also Lightning Protection of Masts and Towers, Lightning Protection Norms and lightning rods and air terminations.