Lightning Protection of Telecom Towers and Antenna Masts: What the Designer Checks

What the tower already has and what is added

External lightning protection of a telecom tower or antenna mast has three parts: an air terminal on top, a down-conductor and an earth-termination system. The tower shaft may serve as the down-conductor if the conditions described below are met. How such a system is built is covered in Lightning protection of masts and towers.

On multi-sided telecom towers, an air terminal, video surveillance and lighting are fitted as extra equipment (see Types of telecom towers). We supply telecom towers complete with a lightning rod: the set includes the air terminal at the top. The down-conductor and the earth electrode are not part of the set.

DSTU EN 62305-3:2021 calls a conductive part a natural component when it was installed for another purpose but can work as part of the lightning protection system (cl. 3.15). The part must stay in its intended place and remain unchanged (cl. 5.1.3). For a steel tower this is an analogy, because the clause is written about buildings.

The top: air terminal rod and protection zone

The design leaves room for an air terminal above the highest antenna, so the tower height is counted together with it (see Mast and telecom tower height).

The protection zone of a rod depends on the calculation method and the system class. The three methods and the parameters by class are in Protection zone calculation for a lightning rod, and the rolling-sphere radius can be estimated in the calculator. For a tower the point is whether antennas, brackets and cable trays on the upper levels fall inside the zone.

Cl. 5.2.5 and Table 3 cover sheet metal and pipes in the air-termination system of a building, so for the wall of the top section of a tower they apply only by analogy; the figures and caveats are in A steel mast as air-termination and down-conductor.

The shaft as a down-conductor and section joints

A metal structure may serve as a down-conductor if electrical continuity between its parts is reliable and its dimensions are not below Table 6 (DSTU EN 62305-3:2021, cl. 5.3.5 a). Again this is an analogy, since the clause is written about parts of structures. The shaft cross-section is compared with Table 6 (a worked example for tubes is in the mast article).

A multi-sided telecom tower is made of bent steel sections joined telescopically or with flanges. They are usually no longer than 12 m. The current passes from section to section at these joints, so the design should show separately how reliable the electrical contact between them is.

The standard advises keeping the number of joints to a minimum and making them reliable: hard soldering, welding, bolts or screws (cl. 5.5.3). How telescopic joints and flanges are made is shown by the design.

Earthing the tower

From the lightning protection point of view, a single integrated earth-termination system is best, suitable for lightning protection, power supply and telecommunications alike (cl. 5.4.1). For a tower this means coordinating the earthing with what is already on the site.

The earthing is made as type A (external electrodes, at least two) or type B (ring electrode or foundation loop; cl. 5.4.2). Electrode lengths, which depend on the system class and soil resistivity, are covered in Pole earthing. The minimum lengths may be ignored if the earthing resistance is below 10 ohm; if the lengths cannot be met and the resistance is higher, type B is used (cl. 5.4.2.1).

Type A electrodes are laid so that their upper ends are at least 0.5 m deep (cl. 5.4.3). The upper part of a vertical electrode that reaches the frost depth the standard advises not to count as working, and adds 0.5 m to the length of a vertical electrode. For bare rock the standard recommends type B.

The recommended earthing resistance is up to 10 ohm at low frequency, if possible (cl. 5.4.1). It is a recommendation, not a hard limit.

A test joint is fitted on every down-conductor except a natural one connected to the foundation earth electrode (cl. 5.3.6); it is opened with a tool only.

Equipment and cables at height

A tower may carry antennas, lighting, lights and video surveillance. Whether this equipment falls under the protection and how it is bonded to the tower is decided by the design.

PUE (2026 edition), cl. 4.2.163, lists radio masts among tall structures whose protective effect may be counted for open switchgear of 15.75 kV and above. If a tower or mast stands on a substation site, this clause may apply to it; the substation design decides. For such equipment, wiring on a lightning rod follows cl. 4.2.167: metal-sheathed cables, or unsheathed cables in metal pipes; the sheath or pipe is earthed, and near the structure the cables run in the ground for at least 10 m. This is a substation rule, not one for every telecom tower.

Inspection after erection and in service

The lightning protection system is inspected during installation, especially when parts will later become inaccessible, after completion and then regularly (DSTU EN 62305-3:2021, Annex E, cl. E.7.1). The intervals the annex recommends and the scope of an inspection are covered in Inspection and maintenance of lightning protection.

Testing covers continuity checks, especially of parts that became inaccessible for visual inspection, and measurement of earth resistance; the earth resistance results are recorded in the inspection report (cl. E.7.2.4).

What to send for choosing a lightning rod

For a tower or mast, give the height, wind region, type and location, and what already stands or will stand on the upper levels: antennas, lighting, video surveillance. Leave blank what you do not know and we will clarify. See also Telecom towers and Lightning rods. Erection of the tower is done by a licensed construction partner company.