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In practice, the requirements shown in Table 5.4.1.2 apply to roofs, it should be ensured that there is a flexible connection
expansion pieces. by means of suitable components or other measures. If this
When using expansion pieces, it must be observed that they flexible connection is not made, there is a risk that the metal
provide flexible length compensation. It is not sufficient to capping of the roof parapet will be damaged by the tempera-
bend the metal wires into an S shape since these manually ture-related change in length.
installed “expansion pieces” are not sufficiently flexible. To compensate for the temperature-related changes in length
When connecting air-termination systems, for example to of the air-termination conductors, expansion pieces must be
metal cappings of the roof parapet surrounding the edges of used for length compensation (Figure 5.4.1.1).

Steel (tZn) Aluminium Copper StSt (V4A) Titanium Tin
Steel (tZn) yes yes no yes yes yes
Aluminium yes yes no yes yes yes
Copper no no yes yes no yes
StSt (V4A) yes yes yes yes yes yes
Titanium yes yes no yes yes yes
Tin yes yes yes yes yes yes
Table 5.4.1 Material combinations

Coefficient of linear expansion α ΔL
Material 1 1 Calculation formula: ΔL = α · L · ΔT
10 6 K Assumed temperature change on the roof: ΔT = 100 K

6 1 mm
Steel 11.5 L = 11.5 10 1m 100K = 0.115cm 1.1
K m
Stainless 6 1 mm
steel 16 L = 16 10 K 1m 100K = 0.16cm 1.6 m

6 1 mm
Copper 17 L = 17 10 1m 100K = 0.17cm 1.7
K m
6 1 mm
Aluminium 23.5 L = 23.5 10 1m 100K = 0.235cm 2.3
K m
Table 5.4.1.1 Calculation of the temperature-related change in length ΔL of metal wires for lightning protection systems

Surface under the fixing of the air-termination system or down conductor Distance of
Material soft, e.g. flat roof with bitumen hard, expansion
or synthetic roof sheetings e.g. pantiles or brickwork pieces in m
• ≈ 15
Steel
• ≤ 20
Stainless steel / • ≈ 10
Copper • ≤ 15
Aluminium • • ≤ 10
Use of expansion pieces, if no other length compensation is provided
Table 5.4.1.2 Expansion pieces in lightning protection – Recommended application

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