---

h₂/?₁+ H, being the height of the air-termination rod over the ground

a_A the protection angle corresponding to the air-termination height h= h,, being the height above the roof surface to be measured (reference plane)

a_? the protection angle corresponds to the height h₂

Figure E.12 - Protection angle method air-termination design

for different heights according to Table 2

The protection angle method has geometrical limits and cannot be applied if H is larger than the rolling sphere radius, r, as defined in Table 2.

If structures on the roof are to be protected with finials and the protection volume of the finials is over the edge of the building, the finials should be placed between the structure and the edge. If this is not possible the rolling sphere method should be applied.

The design of air-termination using the protection angle air-termination design method is also shown in Figures E.13 and E.14 for an isolated LPS and in Figures E.15 and E.16 for a non­isolated LPS.

ІЄС 2680/10

Key 1 air-termination mast

2. protected structure

3. ground being the reference plane

4. intersection between protection cones

5. separation distance according to 6.3

a protection angle complying with Table 2

Figure E.13a - Projection on a vertical plane

NOTE The two circles denote the protected area on the ground as the reference plane.

Figure E.13b - Projection on the horizontal reference plane

Figure E.13 - Isolated external LPS using two isolated air-termination masts
designed according to the protection angle air-termination design method

IEC 2683/10

Figure E.14b - Projection on a vertical
plane perpendicular to the plane
containing the two masts .

Figure Е.14а - Projection on a vertical
plane parallel to that containing two masts

IEC 2682/10

Figure E.14c - Projection on the horizontal
reference plane

IEC 2684/10

Key

1. air-termination mast

2. protected structure

3. protected area on the reference plane

4. horizontal wire air-termination

Sp s₂ separation distances according to 6.3

a protection angle complying with Table 2

NOTE The air-termination system is designed according to the protection angle air-termination design method. The whole structure should be inside the protected volume.

Figure E.14 - Isolated external LPS using two isolated air-termination masts,
interconnected by horizontal catenary wire

Figure Е.15а - Example using one air-termination rod

Figure E.15b - Example using two air-termination rods

Key

1. air-termination rod

2. protected structure

3. assumed reference plane

a protection angle complying with Table 2

NOTE The whole structure should be inside the protected volumes of the air-termination rods.

Figure E.15 - Example of design of an air-termination
of a non-isolated LPS by air-termination rods

/ЕС 2687/10

Figure E.16a - Projection on a vertical plane containing the conductor

Figure E.16b - Projection on the vertical plane perpendicular to the plane containing the conductor

Key

a protection angle complying with Table 2 d₁ distance of horizontal wire from the roof

NOTE The whole structure should be inside the protected volume.

Figure E.16 - Example of design of an air-termination of a non isolated LPS by a
horizontal wire according to the protection angle air-termination design method

If the surface on which the air-termination system is placed is inclined, the axis of the cone which forms the protected zone is not necessarily the air-termination rod, but is instead the perpendicular to the surface on which the air-termination rod is placed; with the top of the cone being equal to the top of the air-termination rod (see Figure E.17).

Key

1. protected volume

2. reference plane

3. air-termination rod

h relevant heights of air-termination according to Table 2

a protection angle

D, D’ limit of the protected area

Figure E.17 - Protected volume of an air- termination rod on a sloped surface
using the protection angle design method

E.5.2.2.2 Rolling sphere method

The rolling sphere method should be used to identify the protected space of parts and areas of a structure when Table 2 excludes the use of the protection angle method.

Applying this method, the positioning of an air-termination system is adequate if no point of the volume to be protected is in contact with a sphere of radius, r, rolling on the ground, around and on top of the structure in all possible directions. Therefore, the sphere should touch only the ground and/or the air-termination system.

The radius r of the rolling sphere depends on the class of LPS (see Table 2). The radius of the rolling sphere is correlated with the peak value of the current in the lightning that strikes the structure: r = 10/ 0.65 where I is defined as kA.

Figure E.18 shows the application of the rolling sphere method to different structures. The sphere of radius r is rolled around and over all the structure until it meets the ground plane or any permanent structure or object in contact with the ground plane which is capable of acting as a conductor of lightning. A striking point could occur where the rolling sphere touches the structure and at such points protection by an air-termination conductor is required

.

Кеу

1 shaded areas are exposed to lightning interception and need protection according Table 2

2 mast on the structure

r radius of rolling sphere according to Table 2

NOTE Protection against side flashes is required according to 5.2.3 and A.2.

Figure E.18 - Design of an LPS air-termination conductor network on a structure
with complicated shape

When the rolling sphere method is applied to drawings of the structure, the structure should be considered from all directions to ensure that no part protrudes into an unprotected zone - a point which might be overlooked if only front, side and plan views on drawings are considered.

The protected space generated by an LPS conductor is the volume not penetrated by the rolling sphere when it is in contact with the conductor and applied to the structure.

Figure E.19 shows the protection afforded by an LPS air-termination system according to the mesh method, rolling sphere method and protection angle method with a general arrangement of air-termination elements.

/ЬС ЖУ7/7О

Key

1. air-termination conductor

2. air-termination rod

3. mesh size

4. down-conductor

5. earthing system with ring conductor

h height of the air-terminal above ground level

a protection angle

Figure E.19 - Design of an LPS air-termination according to the
protection angle method, mesh method and general arrangement
of air-termination elements

In the case of two parallel horizontal LPS air-termination conductors placed above the horizontal reference plane in Figure E.20, the penetration distance p of the rolling sphere below the level of the conductors in the space between the conductors may be calculated:

p

(E.2)

= r — [r² - (cf / 2)²]^1/2

The penetration distance p should be less than h_t minus the height of objects to be protected (the motor in Figure E.20).

ІЕС 2692/10

Key

1. horizontal wires

2. reference plane

3. space protected by two parallel air-termination horizontal wires or two air-termination rods physical height of the air-termination rods above the reference plane

p penetration distance of the rolling sphere

h height of the air-termination according to Table 2 r radius of the rolling sphere

d distance separating two parallel air-terminal horizontal wires or two air-terminal rods

NOTE The penetration distance p of the rolling sphere should be less than h_t minus the largest height of objects to be protected, in order to protect objects in the space between the terminations.

Figure E.20 - Space protected by two parallel air-termination horizontal wires
or two air-termination rods (r > h_t)

The example shown in Figure E.20 is also valid for three or four air-termination rods; for example, four vertical rods placed at the corners of a square with the same applied height h. In this case, d in Figure E.20 corresponds to the diagonals of the square formed by the four rods.

The points at which lightning will strike can be determined using the rolling sphere method. The rolling sphere method can also identify the probability of occurrence of a strike to each point of the building.

Mesh method

For the purpose of protecting flat surfaces, a mesh is considered to protect the whole surface if the following conditions are fulfilled.

1. As mentioned in Annex A, air-termination conductors are positioned on

• roof edge lines,

• roof overhangs,

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

• the lateral surfaces of the structure higher than 60 m at levels higher than 80 % of the height of the structure;

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 accomplished in such a way that the lightning current will always encounter at least two distinct metallic routes to the earth and no metal installation protrudes outside the volume protected by air-termination systems;

NOTE A larger number of down-conductors results in reduction of the separation distance and reduces the electromagnetic field within the building (see 5.3).

4. the air-termination conductors follow as far as possible short and direct routes.

Examples of non-isolated LPS using the air-termination mesh method design are shown in Figure E.21a for a flat-roof structure and in Figure E.21b for a sloped-roof structure. Figure E.21c shows an example of an LPS on a industrial building.

Figure E.21a - LPS air-termination on a flat-roof structure

Key

w_m mesh size

NOTE The mesh size should comply with Table 2.

Figure E.21b - LPS air-termination on a sloped-roof structure

Key

A test joint

NOTE All dimensions should comply with the selected protection level according to Tables 1 and 2.

Figure E.21c -LPS on a shed roof structure

Figure E.21 - Three examples of design of non-isolated LPS air-termination
according to the mesh method air-termination design

E.5.2.3 Air-terminations against flashes to the side on tall structures

In structures higher than 60 m, the topmost 20 % of lateral surfaces should be equipped with air terminals. For the part of this surface to be protected which is below 60 m the protection can be omitted.

NOTE 1 For structures between 60 m and 75 m in height, the area protected need not extend below 60 m.

NOTE 2 If sensitive parts (e.g. electronic equipment) are present on the outside of the wall in the upper part of the building, they should be protected by special air-termination measures, such as horizontal finials, mesh conductors or equivalent.

E.5.2.4 Construction

E.5.2.4.1 General information

The maximum permissible temperature for a conductor will not be exceeded if the cross­section of the conductor conforms to Table 6.

A roof or wall constructed from combustible material should be protected from the dangerous effect of lightning current heating the LPS conductors by using one or more of the following measures:

• reducing the temperature of the conductors by increasing the cross-section;increasing the distance between the conductors and the roof covering (see also 5.2.4);

• inserting a heat-protective layer between the conductors and the flammable material.

NOTE Research has shown that it is advantageous for air-termination rods to have a blunt tip.

E.5.2.4.2 Non-isolated air-termination

Air-termination conductors and down-conductors should be interconnected by means of conductors at the roof level to provide sufficient current distribution over the down-conductors.

Conductors on roofs and the connections of air-termination rods may be fixed to the roof using both conductive or non-conductive spacers and fixtures. The conductors may also be positioned on the surface of a wall if the wall is made of non-combustible material.

Recommended fixing centres for these conductors are shown in Table E.1.

Table E.1 - Suggested fixing centres

On small houses and similar structures with a roof ridge, a roof conductor should be installed on the roof ridge. If the structure is completely within the protected area provided by the roof­ridge conductor, at least two down-conductors should be routed over the gable edges at opposite corners of the structure.

The gutters at the edge of the roof may be used as natural conductors provided that they conform to 5.2.5.

Figures E.22a, E.22b and E.22c depict an example of the arrangement of the conductors on a roof and down-conductors for a sloped roof structure

.

Figure Е.22а - Installation of air-termination
conductor on the ridge of a sloped roof and a roof
down-conductor

ІЕС 2696/10

Figure E.22c - Installation of a down-conductor with
connection to the gutter

IEC 2698/10

ІЕС 2697/10

Figure E.22b - Installation of air-termination rod for
protection of chimney using the protection angle
air-termination design method

Figure E.22d - Installation of a test joint in a down-
conductor and bonding to a drain-pipe

Examples of suitable dimensions:

a 1 m

b 0,15 m (not mandatory)

c 1 m

d as close to the edge as possible

e 0,2 m

f 0,3 m

g 1 m

h 0,05 m

і 0,3 m

j 1,5 m

к 0,5 m

a protection angle according to Table 2

Figure E.22 - Four examples of details of an LPS on a structure with sloped tiled roof

s

Figure Е.23 shows an example of an LPS with concealed conductors.

Conductor,either strip, rod or metallic gutter

Ridge conductor fixed below tile level (see detail)

IEC 2700/10

Key

Concealed conductor

J Vertical air termination (0,3 m high bare vertical rod) at short (<10 m) intervals or strike plates at <5m intervals

Figure E.23 - Air-termination and visually concealed conductors
for buildings less than 20 m high, with sloping roofs

In the case of long structures, additional conductors in accordance with Table 4 should be connected to the air-termination conductors mounted on the roof ridge.

On buildings with large roof overhangs, the roof-ridge conductor should be extended to the end of the ridge. On the gable edge of the roof a conductor should be connected from the roof-ridge conductor to the down-conductor.

As far as is practicable, air-termination conductors, connecting conductors and down­conductors should be installed in a straight route. On non-conducting roofs, the conductor may be placed either under, or preferably over, the roof tiles. Although mounting it under the tiles has the advantage of simplicity and less risk of corrosion, it is better, where adequate fixing methods are available, to install it along the top of the tiles (i.e. externally) so reducing the risk of damage to the tiles should the conductor receive a direct flash. Installing the conductor above the tiles also simplifies inspection. Conductors placed below the tiles should preferably be provided with short vertical finials which protrude above roof level and are spaced not more than 10 m apart. Appropriate exposed metal plates may also be used (see Figure E.23) provided they are spaced not more than 5 m apart.

On structures with flat roofs, the perimeter conductors should be installed as close to the outer edges of the roof as practicable.

When the roof surface exceeds the mesh size stipulated in Table 2, additional air-termination conductors should be installed.

Figures E.22a, E.22b and E.22c show examples of the construction details of fixtures for air­termination conductors on the sloped roof of a structure. Figure E.24 provides an example of construction details for fixtures on a flat roof

.

Key

a 500 mm to 1 000 mm, see Table E.1

1 roof parapet

2 joint

3 flexible conductor

4 T-joints

5 air-termination conductor fixture

6 LPS passing through a watertight bushing

7 steel girder

8 joint

NOTE Metallic covering on the roof parapet is used as an air-termination conductor and is connected to the steel girder used as a natural down-conductor of the LPS.

Figure E.24 - Construction of an LPS using natural components
on the roof of the structure

Figure E.25 shows the positioning of the external LPS on a structure with a flat roof made of isolating material such as wood or bricks. The roof fixtures are within the space to be protected. On high structures, a ring connected to all down-conductors is installed on the facade. The distances between these ring conductors should comply with 5.3.1. Ring conductors below the level of the rolling sphere radius are needed as equipotentialization conductors.

Key

1. air-termination rod

2. horizontal air-termination conductor

3. down-conductor

4. T-type joint

5. cross-type Joint

6. TEST joint

7. В-type earthing arrangement, ring earth electrode

8. equipotentialization ring conductor

9. flat roof with roof fixture

10. terminal for connecting the equipotentialization bar of the internal LPS

11. vertical earth rod

NOTE An equipotentialization ring is applied. The distance between the down-conductors complies with the requirements in Table 4.

Figure E.25 - Positioning of the external LPS on a structure made of isolating material e.g. wood or bricks with a height up to 60 m with flat roof and with roof fixtures

LPS conductors and rods should be mechanically secured so that they are capable of withstanding stress due to wind or weather and work carried out on the roof surface.

Metal covering provided for mechanical protection of outer walls parapet capping may be used as a natural component of the air-termination, according to 5.2.5, if there is no risk of fire ignition by melting metal. The combustibility depends on the type of material under the metal cladding. The combustibility of the material employed should be confirmed by the contractor.

The roof sealing arrangement on metallic roofs, as with other types of roof, can be perforated by a lightning flash. In such a case, water can penetrate and leak through the roof at a point far from the striking point. If this possibility is to be avoided, an air-termination system should be installed.

Light cupolas and smoke and heat outlet flaps are normally closed. The design for the protection of such flaps should be discussed with the purchaser/owner of the building to decide whether protection should be applicable for the flaps in the open, closed and all intermediate positions.

Roof coverings of conductive sheet which do not conform to 5.2.5 may be used as air­terminations where melting at the striking point of lightning can be accepted. If this is not acceptable, the conductive roof sheeting should be protected by an air-termination system of sufficient height (see Figure E.20 and Figure E.26).

Key

r radius of the rolling sphere, Table 2

a air-termination conductors