Lightning Protection Materials and Cross-Sections: Steel, Copper, Aluminium

What lightning protection parts are made of

Table 5 of the standard lists copper, hot-dip galvanised steel, copper-clad steel, stainless steel, aluminium and lead. For each material it states the form that may be used in air, in soil and in concrete. Other materials are acceptable if their mechanical, electrical and corrosion properties are equivalent (clause 5.5.1).

We make poles and masts from steel and hot-dip galvanise them, so most of what follows is about hot-dip galvanised steel. Copper and aluminium are covered for comparison: the limits that come with them affect the choice of fixings, clamps and earthing.

The minimum cross-sections of air terminals, down-conductors and earth electrodes do not depend on the lightning protection class (Tables 6 and 7, clause 5.6.2): the figures for class I and class IV are the same. The class affects the protection zone and the spacing of down-conductors, not the cross-section. Components must comply with the EN 62561 series and be tested to it; in Ukraine these are DSTU EN 62561-1:2019 (connection components) and DSTU EN IEC 62561-2:2019 (conductors and earth electrodes).

Minimum cross-sections of air terminals and down-conductors

Table 6 (clause 5.6.2) gives the smallest cross-sectional area for air-termination conductors, air-termination rods and down-conductors. Values are in mm²; the table below shows three forms: tape, solid round and stranded.

DSTU EN 62305-3:2021, Table 6, abridged; the standard also lists copper-clad aluminium alloy and copper-clad steel. Area in mm².

Rods, sheet and the notes to the table

For an air-termination rod or an earth rod made of solid round metal, Table 6 (note c) requires 176 mm²: this applies to copper, aluminium alloy, hot-dip galvanised steel and stainless steel. Where wind or other mechanical loading is not critical, an air-termination rod 9.5 mm in diameter and 1 m long is acceptable. For a rod exposed to wind this relaxation does not apply: the designer makes the choice.

For a copper conductor, 50 mm² may in some applications be reduced to 25 mm² if mechanical strength is not needed; the fixing spacing is then reduced (note b). For stainless steel, where heating and mechanical strength matter, the value must be increased to 75 mm² (note d).

If a sheet or tube serves as the air terminal, Table 3 applies: steel needs 4 mm, copper 5 mm and aluminium 7 mm so the sheet is not punctured. Only for sheet, where puncture, local overheating or ignition do not matter, is 0.5 mm (steel, copper) or 0.65 mm (aluminium) enough. How this table is read for a steel mast is covered in Steel mast as air terminal and down-conductor.

Bonding conductors joining different bars, or a bar to the earth-termination system, must be no thinner than 16 mm² for copper, 25 mm² for aluminium and 50 mm² for steel (Table 8). Conductors from internal metal installations to the bar are smaller: 6, 10 and 16 mm² respectively (Table 9).

Earth electrodes: materials and sizes

Table 7 (clause 5.6.2) gives the minimum sizes of electrodes in the ground. A selection for four materials:

DSTU EN 62305-3:2021, Table 7, abridged; plates, profiles and lattice electrodes are not shown here. Bare steel is embedded in concrete at least 50 mm (note b).

Corrosion and incompatible pairs

Under Table 5 aluminium is unsuitable for earth electrodes in soil and in concrete. In air aluminium does well where sulphur and chloride levels are low; alkali solutions increase corrosion.

For hot-dip galvanised steel in the ground the standard favours solid conductors over stranded ones: stranded conductors corrode faster and are most vulnerable where they enter or leave soil or concrete (Table 5, note b). In clay or wet soil zinc can corrode, and galvanised steel running from concrete into soil is at risk because of the neighbouring concrete (Table 5, notes c, d).

Galvanic pairs: according to Table 5, galvanic contact with copper can destroy both hot-dip galvanised steel and aluminium. Lead is just as sensitive to copper and stainless steel. So where copper ends up next to zinc, an insulating spacer is fitted if electrical contact is not needed at that point. Copper-aluminium connectors are avoided; if unavoidable, they are welded or fitted with an intermediate copper-aluminium sheet layer (Annex E).

General measures from Annex E: do not use unsuitable metals in an aggressive environment, allow a generous cross-section, keep moisture out of unwelded joints, and protect sensitive metals with a sheath or coating. Unprotected steel conductors are to be hot-dip galvanised. For zinc thickness see Zinc coating thickness to DSTU EN ISO 1461:2024.

What to put in the specification

A design or an order is best written so that no questions remain on site:

• material and form of each element: tape, solid round, stranded, tube;
• minimum cross-section from Table 6 or 7 and whether there is a corrosion allowance;
• environment: air, soil, concrete (it decides which material is acceptable at all);
• steel coating: hot-dip galvanising, and whether copper or aluminium is nearby;
• compliance of components with the EN 62561 series (clamps, connectors, test joints).

The designer decides all this; the article does not describe work at height or electrical connections, which are done by specialists. For the wider picture of the standards see Lightning protection standards; for choosing the mast itself, Lightning protection for masts and towers; for earthing, Pole earthing.

What to send so we can select a lightning rod

Tell us what the object is, the height and protection zone the design gives, and what material it requires for the air terminal and down-conductor. If a specification exists, attach it. Leave blank what you do not know: we will clarify.

We will suggest a pole or mast with an air terminal from the Lightning rods 6–40 m catalogue or from the Lightning rods and air terminals section. Installation is done by a licensed construction partner company. This article does not replace a lightning protection design.