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≤ 1.0 m ≈ 0.15 m ≈ 0.3 m α e ≈ 0.2 m
appropriate
distance

≈ 0.3 m e
1.5 m

≤ 1.0 m 0.05 m
≤ 1.0 m 0.5 m

as close as
possible to
the edge

Figure 5.4.1 Examples (details) of an external lightning protection system installed on a build- Figure 5.4.2 Air-termination rod for a
ing with a sloped tiled roof chimney

building

corrosion
≤ 1 m protection
≥ 0.5 m 0.3 m
0.3 m

≈ 1 m

Figure 5.4.3 Application on a flat roof Figure 5.4.4 Dimensions for ring earth Figure 5.4.5 Points threatened by cor-
electrodes rosion

Provided that no particularly aggressive environmental influ- In many cases, older regulations and stipulations generally rec-
ences must be taken into account, the material combinations ommended to install an expansion piece approximately every
(air-termination systems, down conductors and structural 20 m. This recommendation was based on the use of steel
parts) according to Table 5.4.1 have proven to be successful wires which used to be the usual and sole material. The higher
in practice. These values are empirical values. coefficients of linear expansion of stainless steel, copper and
especially aluminium were not taken into account.
In the course of the year, temperature changes of 100 K must
5.4.1 Changes in length of metal wires be expected on and around the roof. The resulting changes
in length for the different metal wire materials are shown in
The temperature-related changes in length of air-termination Table 5.4.1.1. It can be seen that the temperature-related
systems and down conductors are often underestimated in change in length between steel and aluminium differs by a
practice. factor of 2.

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