Page 69 - 35_DS702_E_2014_Lightning_Protection_Guide

Class of LPS Mesh size α° 80
I 5 x 5 m 70
60
II 10 x 10 m
50
III 15 x 15 m
40
IV 20 x 20 m 30
Table 5.1.1.3 Mesh size 20 I II III IV
10
0
e.g. gutter 0 2 10 20 30 40 50 60
h [m]
Figure 5.1.1.12 Protective angle α as a function of height h
depending on the class of LPS

α° α°
h 1
Figure 5.1.1.10 Meshed air-termination system

rolling sphere

r
Figure 5.1.1.13 Cone-shaped protected volume
protective
angle termination system, the individual meshes can be positioned
air-termi- same surface areas as desired.
nation rod The air-termination conductors on the outer edges of the struc-
α° ground area ture must be laid as close to the edges as possible.

The metal capping of the roof parapet can serve as an air-ter-
Figure 5.1.1.11 Protective angle and comparable radius of the roll- mination conductor and / or a down conductor if the required
ing sphere minimum dimensions for natural components of the air-termi-
nation system are complied with (Figure 5.1.1.10).
Mesh method Protective angle method
A “meshed” air-termination system can be used universally The protective angle method is derived from the electric-geo-
regardless of the height of the building and shape of the roof. metric lightning model. The protective angle is determined by
A meshed air-termination network with a mesh size according the radius of the rolling sphere. The protective angle, which is
to the class of LPS is arranged on the roofing (Table 5.1.1.3). comparable with the radius of the rolling sphere, is given when
a slope intersects the rolling sphere in such a way that the
To simplify matters, the sag of the rolling sphere is assumed to resulting areas have the same size (Figure 5.1.1.11).
be zero for a meshed air-termination system. This method must be used for buildings with symmetrical di-
By using the ridge and the outer edges of the building as well mensions (e.g. steep roof) or roof-mounted structures (e.g. an-
as the metal natural parts of the building serving as an air- tennas, ventilation pipes).

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