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The positioning shall be as follows:

1. If the air-termination consists of rods on separate masts (or one mast) not made of metal or interconnected reinforcing steel, at least one down-conductor is needed for each mast. No additional down-conductors are required for masts made of metal or interconnected reinforcing steel.

NOTE In several countries, the use of reinforced concrete as a part of the LPS is not allowed.

2. If the air-termination consists of catenary wires (or one wire), at least one down-conductor is needed at each supporting structure.

3. If the air-termination forms a network of conductors, one down-conductor is needed at least at each supporting wire end.

For each non-isolated LPS the number of down-conductors shall be not less than two and should be distributed around the perimeter of the structure to be protected, subject to architectural and practical constraints.

An equal spacing of the down-conductors is preferred around the perimeter. Typical preferred values of the distance between down-conductors are given in Table 4.

NOTE The value of the distance between down-conductors is correlated with the separation distance given in 6.3.

Table 4 - Typical preferred values of the distance between down-conductors according to the class of LPS

A down-conductor should be installed at each exposed corner of the structure, where this is possible.

The down-conductors shall be installed so that, as far as practicable, they form a direct continuation of the air-termination conductors.

Down-conductors shall be installed straight and vertical such that they provide the shortest and most direct path to earth. The formation of loops shall be avoided, but where this is not possible, the distance s, measured across the gap between two points on the conductor and the length, /, of the conductor between those points (see Figure 2) shall conform to 6.3.

Figure 2 - Loop in a down-conductor

Down-conductors, even if covered in insulating material, shall not be installed in gutters or water spouts.

NOTE The effects of moisture in the gutters lead to intensive corrosion of the down-conductor.

It is recommended that the down-conductors be positioned such that a separation distance in accordance with 6.3 is provided between them and any doors and windows.

Down-conductors of an LPS not isolated from the structure to be protected may be installed as follows:

• if the wall is made of non-combustible material, the down-conductors may be positioned on the surface or in the wall;

• if the wall is made of readily-combustible material the down-conductors may be positioned on the surface of the wall, provided that their temperature rise due to the passage of lightning current is not dangerous for the material of the wall;

• if the wall is made of readily-combustible material and the temperature rise of down­conductors is dangerous, the down-conductors shall be placed in such a way that the distance between them and the wall is always greater than 0,1 m. Mounting brackets may be in contact with the wall.

When the distance from down-conductor to a combustible material cannot be assured, the cross-section of the steel or thermal equivalent conductor shall be not less than 100 mm².

The following parts of the structure may be used as natural down-conductors: a) the metal installations provided tha

• tthe electrical continuity between the various parts is made durable in accordance with 5.5.3,

• their dimensions are at least equal to that specified in Table 6 for standard down­conductors.

Piping carrying readily-combustible or explosive mixtures shall not be considered as a down-conductor natural component if the gasket in the flange couplings is not metallic or if the flange-sides are not otherwise properly bonded.

NOTE 1 Metal installations may be clad with insulating material.

2. the metal of the electrically-continuous reinforced concrete framework of the structure;

NOTE 2 With prefabricated reinforced concrete, it is important to establish interconnection points between the reinforcing elements. It is also important that reinforced concrete contains a conductive connection between the interconnection points. The individual parts should be connected on-site during assembly (see Annex E).

NOTE 3 In the case of pre-stressed concrete, attention should be paid to the risk of causing unacceptable mechanical consequences, due either to lightning current or as a result of the connection to the lightning protection system.

2. the interconnected steel framework of the structure;

NOTE 4 Ring conductors are not necessary if the metal framework of steel structures or the interconnected reinforcing steel of the structure is used as down-conductors.

2. the facade elements, profile rails and metallic sub-constructions of facades, provided that

• their dimensions conform to the requirements for down-conductors (see 5.6.2) and that for metal sheets or metal pipes thicknesses shall be not less than 0,5 mm,

• their electrical continuity in a vertical direction conforms to the requirements of 5.5.3.

NOTE 5 For more information, see Annex E.

5.3.6 Test joints

At the connection of the earth-termination, a test joint should be fitted on each down­conductor, except in the case of natural down-conductors combined with foundation earth electrodes.

For measuring purposes, the joint shall be capable of being opened with the aid of a tool. In normal use it shall remain closed.

5.4 Earth-termination system

When dealing with the dispersion of the lightning current (high frequency behaviour) into the ground, whilst minimizing any potentially dangerous overvoltages, the shape and dimensions of the earth-termination system are the important criteria. In general, a low earthing resistance (if possible lower than 10 Q when measured at low frequency) is recommended.

From the viewpoint of lightning protection, a single integrated structure earth-termination system is preferable and is suitable for all purposes (i.e. lightning protection, power systems and telecommunication systems).

Earth-termination systems shall be bonded in accordance with the requirements of 6.2.

NOTE 1 The conditions of separation and bonding of other earth-termination systems are usually determined by the appropriate national authorities.

NOTE 2 Serious corrosion problems can occur when earthing systems made of different materials are connected to each other.

For earth-termination systems, two basic types of earth electrode arrangements apply.

This type of arrangement comprises horizontal or vertical earth electrodes installed outside the structure to be protected connected to each down-conductor or foundation earth electrodes not forming a closed loop.

In type A arrangements, the total number of earth electrodes shall be not less than two.

о

500

1 000 1 500

2 000 2 500 3 000

P M

IEC 2648/10

NOTE Classes III and IV are independent of soil resistivity.

Figure 3 - Minimum length /₁of each earth electrode according to the class of LPS

The minimum length of each earth electrode at the base of each down-conductor is

• /₁ for horizontal electrodes, or

• 0,5/₁ for vertical (or inclined) electrodes,

where is the minimum length of horizontal electrodes shown in the relevant part of Figure 3.

For combined (vertical or horizontal) electrodes, the total length shall be considered.

The minimum lengths stated in Figure 3 may be disregarded provided that an earthing resistance of the earth-termination system less than 10 Q (measured at a frequency different from the power frequency and its multiple in order to avoid interference) is achieved.

NOTE 1 When the above-mentioned requirements cannot be met, a type В earth arrangement shall be used.

NOTE 2 Reduction of earthing resistance by the extension of earth electrodes is practically convenient up to 60 m. In soil with resistivity higher than 3 000 !!m the use of type В earth electrodes or earthing enhancing compounds is recommended.

NOTE 3 For further information, refer to Annex E.5.4.2.2 Type В arrangement

This type of arrangement comprises either a ring conductor external to the structure to be protected, in contact with the soil for at least 80 % of its total length, or a foundation earth electrode forming a closed loop. Such earth electrodes may also be meshed.

NOTE Although 20 % may not be in contact with the soil, the ring conductor must always be completely connected throughout its total length.

For the ring earth electrode (or foundation earth electrode), the mean radius r_e of the area enclosed by the ring earth electrode (or foundation earth electrode) shall be not less than the value

r_e>/i (1)

where /₁ is represented in Figure 3 according to LPS class I, II, III and IV.

When the required value of /₁ is larger than the convenient value of r_e, additional horizontal or vertical (or inclined) electrodes shall be added with individual lengths /_r (horizontal) and /_v (vertical) given by the following equations:

l_r = /1 - r_e (2)

and /_v = (^ - r_e) / 2 (3)

It is recommended that the number of electrodes shall be not less than the number of the down-conductors, with a minimum of two.

The additional electrodes should be connected to the ring earth electrode at points where the down-conductors are connected and, for as many as possible, equidistantly.

The ring earth electrode (type В arrangement) should preferably be buried at a depth of at least 0,5 m and at a distance of about 1 m away from the external walls.

The earth electrodes (type A arrangement) shall be installed at a depth of upper end at least 0,5 m and distributed as uniformly as possible to minimize electrical coupling effects in the earth.

NOTE 1 If the type A earth electrode is positioned within an inspection housing which, in turn, is located in high resistance paving or adjoining concrete, then the 0,5 m requirement can be disregarded.

Earth electrodes shall be installed in such a way as to allow inspection during construction.

The embedded depth and the type of earth electrodes shall be such as to minimize the effects of corrosion, soil drying and freezing and thereby stabilize the conventional earth resistance. It is recommended that the upper part of a vertical earth electrode equal to the depth of freezing soil should not be regarded as being effective under frost conditions.

NOTE 2 Hence, for every vertical electrode, 0,5 m should be added to the value of the length /₁, calculated in 5.4.2.1 and 5.4.2.2.

For bare solid rock, a type В earthing arrangement is recommended.

For structures with extensive electronic systems or with high risk of fire, type В earthing arrangement is preferable.

Interconnected reinforcing steel in concrete foundations in accordance with 5.6, or other suitable underground metal structures, should preferably be used as an earth electrode. When the metallic reinforcement in concrete is used as an earth electrode, special care shall be exercised at the interconnections to prevent mechanical splitting of the concrete.

NOTE 1 In the case of pre-stressed concrete, consideration should be given to the consequences of the passage of lightning discharge currents which may produce unacceptable mechanical stresses.

NOTE 2 If a foundation earth electrode is used, a long-term increase in earthing resistance is possible.

NOTE 3 More extensive information on this topic is reported in Annex E.

Components of LPS shall withstand the electromagnetic effects of lightning current and predictable accidental stresses without being damaged. This can be achieved by choosing components that have successfully been tested in accordance with the future IEC 62561 series.

Components of an LPS shall be manufactured from the materials listed in Table 5 or from other materials with equivalent mechanical, electrical and chemical (corrosion) performance characteristics.

NOTE Components made of material other than metal may be used for fixing

.

Table 5 - LPS materials and conditions of use^a

This table gives general guidance only. In special circumstances more careful corrosion immunity considerations are required (see Annex E).

Stranded conductors are more vulnerable to corrosion than solid conductors. Stranded conductors are also vulnerable where they enter or exit earth/concrete positions. This is the reason why stranded galvanized steel is not recommended in earth.

Galvanized steel may be corroded in clay soil or moist soil.

Galvanized steel in concrete should not extend into the soil due to possible corrosion of the steel just outside the concrete.

Galvanized steel in contact with reinforcement steel in concrete should not be used in coastal areas where there may be salt in the ground water

Use of lead in the earth is often banned or restricted due to environmental concerns.

Air-terminations and down-conductors shall be firmly fixed so that the electrodynamic or accidental mechanical forces (for instance vibrations, slipping of slabs of snow, thermal expansion, etc.) will not cause conductors to break or loosen (see Annex D of IEC 62305-1:2010).

NOTE Recommended distances between fixings are reported in Table E.1.

The number of connections along the conductors shall be kept to a minimum. Connections shall be made secure by such means as brazing, welding, clamping, crimping, seaming, screwing or bolting.To achieve this, connections of steelwork within reinforced concrete structures shall conform to 4.3 and shall comply with the requirements and tests according to the future IEC 62561-1.

Material and its dimensions shall be chosen bearing in mind the possibility of corrosion either of the structure to be protected or of the LPS.

Configurations and minimum cross-sectional areas of air-termination conductors, air­termination rods and down-conductors are given in Table 6 and shall comply with the requirements and tests according to the future IEC 62561 series..

Configurations and minimum dimensions of earth electrodes are given in Table 7 and shall comply with the requirements and tests according to the future IEC 62561 series

.

Table 6 - Material, configuration and minimum cross-sectional area of air-termination conductors, air-termination rods, earth lead-in rods and down-conductors³

Mechanical and electrical characteristics as well as corrosion resistance properties shall meet the requirements of the future IEC 62561 series.

50 mm² (8 mm diameter) may be reduced to 25 mm² in certain applications where mechanical strength is not an essential requirement. Consideration should in this case, be given to reducing the spacing between the fasteners.

Applicable for air-termination rods and earth lead-in rods. For air-termination rods where mechanical stress such as wind loading is not critical, a 9,5 mm diameter, 1 m long rod may be used.

If thermal and mechanical considerations are important then these values should be increased to 75 mm².

Table 7 - Material, configuration and minimum dimensions of earth electrodes^{3 e}