---

a protection angle according to Table 2

Figure A.1 - Volume protected by a vertical air-termination rod

Key

/і₁ physical height of an air-termination rod

NOTE The protection angle a₁ corresponds to the air-termination height h_v being the height above the roof surface to be protected; the protection angle a₂ corresponds to the height h₂ = h₁ + H the ground being the reference plane; a₁ is related to h₁ and a₂ is related to h₂.

Figure A.2 - Volume protected by a vertical air-termination rod

A.1.3 Volume protected by a wire air-termination system

The volume protected by a wire is defined by the composition of the volume protected by virtual vertical rods having vertexes on the wire. Examples of the protected volume are given in Figure A.3.

NOTE See Figure A.1 for key.

Figure A.3 - Volume protected by a wire air-termination systemА.1.4 Volume protected by wires combined in a mesh

The volume protected by wires combined in a mesh is defined by a combination of the protected volume determined by the single conductors forming the mesh.

Examples of the volume protected by wires combined in a mesh is given in Figures A.4 and A.5.

IEC 2652/10

Figure A.4 - Volume protected by isolated wires combined in a mesh according
to the protection angle method and rolling sphere methodWm as determined byTable 2

I EC 2653/10

Figure A.5 - Volume protected by non-isolated wires combined in a mesh according
to the mesh method and the protection angle method

A.2 Positioning of the air-termination system utilizing the rolling sphere method

Applying this method, the positioning of the air-termination system is adequate if no point of the structure to be protected comes into contact with a sphere with radius, r, depending on the class of LPS (see Table 2), rolling around and on top of the structure in all possible directions. In this way, the sphere only touches the air-termination system (see Figure A.6).

On all structures higher than the rolling sphere radius r, flashes to the side of structure may occur. Each lateral point of the structure touched by the rolling sphere is a possible point of strike. However, the probability for flashes to the sides is generally negligible for structures lower than 60 m.

For taller structures, the major part of all flashes will hit the top, horizontal leading edges and corners of the structure. Only a few per cent of all flashes will be to the side of the structure.

Moreover, observation data show that the probability of flashes to the sides decreases rapidly as the height of the point of strike on tall structures when measured from the ground. Therefore consideration should be given to install a lateral air-termination system on the upper part of tall structures (typically the top 20 % of the height of the structure). In this casethe rolling sphere method will be applied only to the positioning of the air-termination system of the upper part of the structure.

IEC 2654/10

NOTE The rolling sphere radius, r, should comply with the selected class of LPS (see Table 2).

Figure A.6 - Design of an air-termination system according to the rolling sphere method

A.3 Positioning of the air-termination system utilizing the mesh method

For the purposes of protecting flat surfaces, a mesh is considered to protect the whole surface, dependent upon all of the following conditions being fulfilled:

1. Air-termination conductors are positioned

• on roof edge lines,

• on roof overhangs,

• on roof ridge lines, if the slope of the roof exceeds 1/10.

NOTE 1 The mesh method is suitable for horizontal and inclined roofs with no curvature.

NOTE 2 The mesh method is suitable for flat lateral surfaces to protect against side flashes.

NOTE 3 If the slope of the roof exceeds 1/10, parallel air-termination conductors, instead of a mesh, may be used provided the distance between the conductors is not greater than the required mesh width.

2. The mesh dimensions of the air-termination network are not greater than the values given in Table 2.

3. The network of the air-termination system is constructed in such a way that the lightning current will always encounter at least two distinct metal routes to earth-termination.

4. No metal installation protrudes outside the volume protected by air-termination systems.

NOTE 4 Further information can be found in Annex E.

The air-termination conductors follow, as far as possible, the shortest and most direct route

.Annex В
(normative)

Minimum cross-section of the entering cable screen
in order to avoid dangerous sparking

The overvoltages between the active conductors and the screen of a cable may cause dangerous sparking due to the lightning current carried by the screen. The overvoltages depend on the material, the dimensions of the screen, and the length and positioning of the cable.

The minimum value S_CM,_N (in mm²) of the cross-sectional area of the screen to avoid dangerous sparking is given by:

$cmin ⁼ Uf ^xPc ^x ^-c ^x 10⁶)! Uw (^mm2) (B.1)

where

/_F is the current flowing on the screen, in kA;

p_c is the resistivity of the screen, in Om;

L_c is the cable length, in m (see Table B.1);

U_w is the impulse withstand voltage of the electrical/electronic system fed by the cable, in kV.

Table B.1 - Cable length to be considered according to the condition of the screen

NOTE It should be ascertained whether an unacceptable temperature rise for the insulation of the line could occur when the lightning current flows along the line shield or the line conductors. For detailed information, see IEC 62305-4.

The limits of the current are given:

• for copper shielded cables, by /_F = 8 x S_c; and

• for unshielded cables, by /_F= 8 x n' x S'_c

where

/_F is the current on the screen, in kA;

n' is the number of conductors;

S_c is the cross-section of the screen, in mm²;

S’_c is the cross-section of each conductor, in mm².Annex С
(informative)

Evaluation of the separation distance s

The partitioning coefficient k_c of the lightning current amongst the air-terminations/down- conductors depends on the type of air-termination system, on the overall number, n, and on the position of the down-conductors and on the interconnecting ring conductors, and on the type of earth-termination system.

NOTE 1 The necessary separation distance depends on the voltage drop of the shortest path from the point where the separation distance is to be considered, to the nearest equipotential bonding point.

NOTE 2 The information in this annex applies for all type В earthing arrangements and for type A earthing arrangements, provided that the earth resistance of neighbouring earth electrodes do not differ by more than a factor of 2. If the earth resistances of single earth electrodes differ by more than a factor of 2, k_c = 1 is to be assumed.

When the air-terminations or down-conductors have the constant value of current flowing over the lengths of the conductors, Figures С.1, C.2 and C.3 apply (see 6.3.2. Simplified approach).

IEC 2655/10

h + c

2h + c

Figure C.1 - Values of coefficient k_cin the case of a wire air-termination system

— н 0,1 + 0,2 х 1

2п 1

Key

п total number of down-conductors

c distance of a down-conductor to the next down-conductor

h spacing (or height) between ring conductors

NOTE 1 The equation for k_c is an approximation for cubic structures and for n a 4. The values of h and c are assumed to be in the range of 3 m to 20 m.

NOTE 2 If internal down-conductors exist, they should be taken into account in the number n.

F

IEC 2108/05

igure С.3 (continued overleaf)

F

IEC 2108/05

igure С.З - Values of coefficient k_cin the case of a sloped roof
with air-termination on the ridge

к

^db~ ^sb⁼Т~^{х к}с2^Х'b

к

^d9-^SS=-jT^X{кс2ХZ9 ^{+ кс3 Х Ьз + кс4 Хh4>>}

d_r> s_r = —^L x к „о x /

СО/. Со С

^df - ^sf ⁼ "Г ^Х <^кс1 ^х 4 ^+кс2 ^{х Л}₂)

К

к і — ь 0,1 + 0,2 х

2«

/е_с2 = — + 0,1
п

к_с3= - + 0,01 ^CJп

^кс4~ п

^кст ^кс4 П

total number of down-conductors spacing between down-conductors spacing (height) between ring conductors total number of levels

distance to the nearest down-conductor height above the bonding point

NOTE If internal down-conductors exist, they should be taken into account in the number n.

Figure C.4 - Examples of calculation of the separation distance in the case of multiple down-conductors with an interconnecting ring of the down-conductors at each level

0,12

0JJ6

0,06

0,5

Meshed air-termination system (e.g. acc. to LPS HI)

Number of down­conductors (e.g. acc. to LPS 111) n — 24 1/n = 0,042

0,2

0,042

0,25

0,5

0,12

0,25

к_с Fac or

Down-conductor

s - к, (k_ci ■ /і + k_c2■ І2 ⁺+ к

IEC 2658/10

Key

А, В, C injection points

NOTE 1 Rules for current partitioning:

1. Injection point

Current is divided by the number of possible current paths at the injection point into the meshed air-termination system.

2. Further junctions (joints)

Current is reduced by 50 % at any further joint of the air-termination mesh.

3. Down-conductor

Current is again reduced by 50 %, but the value of k_c must not be less than 1/n.

(n ... total number of down-conductors)

NOTE 2 Values of k_c have to be considered from the point of strike to the edge of the roof. The path along the roof edge to the down-conductor does not need to be considered. The values of k_c along the down-conductors depend on the value of k_c of the connected air-termination at the edge of the roof.

NOTE 3 As shown above, if there are fewer meshes from the point of strike to the edge of the roof, only the relevant values of k_c, beginning from the point where the proximity distance is to be considered, have to be used.

NOTE 4 If internal down-conductors exist, they should be taken into account in evaluating the number n.

Figure C.5 - Values of coefficient k_cin the case of a meshed air-termination system,
with a multiple down-conductors system

Annex D

(normative)

Additional information for LPS in the case of structures
with a risk of explosion

D.1 General

This annex supplies additional requirements for the design, construction, extension and modification of lightning protection systems for structures with a risk of explosion.

NOTE Information provided in this annex is based on practically proven configurations of lightning protection systems installed in applications where a danger of explosion exists. The authority having jurisdiction may give other requirements.

D.2 Additional terms and definitions

In addition to the terms and definitions of Clause 3, the terms and definitions of IEC 60079­14:2007, as well as the following terms and definitions, are applicable to this annex.

D.2.1

solid explosive material

solid chemical compound, mixture, or device with explosion as its primary or common purpose

D.2.2 zone 0 place in which an explosive atmosphere consisting of a mixture of air and flammable substances in the form of gas, vapour or mist is present continuously or for long periods or frequently

[IEC 60050-426:2008, 426-03-03, modified] ^[4]

D.2.3 zone 1 place in which an explosive atmosphere consisting of a mixture of air and flammable substances in the form of gas, vapour or mist is likely to occur in normal operation occasionally

[IEC 60050-426:2008, 426-03-04, modified]^[4]

D.2.4 zone 2 place in which an explosive atmosphere consisting of a mixture of air and flammable substances in the form of gas, vapour or mist is not likely to occur in normal operation but, if it does occur, will persist for a short period only

NOTE 1 In this definition, the word "persist" means the total time for which the flammable atmosphere will exist. This will normally comprise the total of the duration of the release, plus the time taken for the flammable atmosphere to disperse after the release has stopped.

NOTE 2 Indications of the frequency of the occurrence and duration may be taken from codes relating to specific industries or applications.

[IEC 60050-426:2008, 426-03-05, modified]'⁴

¹D.2.5

zone 20

place in which an explosive atmosphere, in the form of a cloud of combustible dust in air, is present continuously, or for long periods, or frequently

[IEC 60079-10-2:2009, 6.2, modified]

D.2.6

zone 21

place in which an explosive atmosphere in the form of a cloud of combustible dust in air, is likely to occur in normal operation occasionally

[IEC 60079-10-2:2009, 6.2, modified]

D.2.7

zone 22

place in which an explosive atmosphere in the form of a cloud of combustible dust in air is not likely to occur in normal operation but, if it does occur, will persist for a short period only

[IEC 60079-10-2:2009, 6.2, modified]

D.3 Basic requirements

D.3.1 General

The lightning protection system shall be designed and installed in such a manner that, in case of a direct lightning flash, there are no melting or spraying effects except at the striking point.

NOTE 1 Sparks or damaging impact at the striking point may also be experienced. This should be taken into consideration in the determination of air-termination device locations. Down-conductors should be installed in such a way that the auto-ignition temperature given by the source of the relative hazardous area are not exceeded in those applications where it is not possible to install down-conductors outside of the hazardous area.

NOTE 2 Due to a lightning stroke, an impact on electrical equipment cannot be avoided in every case.

D.3.2 Required information

The lightning protection system installer/designer shall be provided with drawings of the plant(s) to be protected, with the areas in which solid explosive material will be handled or stored or hazardous areas according to IEC 60079-10-1 and IEC 60079-10-2 appropriately marked.