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lamps, smoke extraction systems and other equipment con-
nected to the electrical low-voltage system (Figure 5.1.11.1).

In accordance with the relevant lightning protection standards
of the IEC 62305 (EN 62305) series, these roof-mounted struc-
tures can be protected from direct lightning strikes by means
of isolated air-termination systems. To this end, both the air-
termination systems such as air-termination rods, air-termina-
tion tips or air-termination meshes and the down conductors
are isolated, in other words they have a sufficient separation
distance from the roof-mounted structures located in the pro-
tected volume. The installation of an isolated lightning protec-
tion system creates a volume protected against direct lightning
strikes and also prevents partial lightning currents from en-
tering the building. This is important because sensitive electri-
cal / electronic equipment can be interfered with or destroyed
by the injected partial lightning currents.
Extended roof-mounted structures are also equipped with a
system of isolated air-termination systems. These are connect-
Figure 5.1.11.1 Protection against direct lightning strikes by means ed with each other and with the earth-termination system. The
of self-supporting air-termination rods size of the protected volume depends e.g. on the number and
height of the air-termination systems installed.
A single air-termination rod is sufficient to provide protec-
5.1.11 Air-termination rods subjected to wind tion for small roof-mounted structures. To this end, the rolling
loads sphere method in accordance with IEC 62305-3 (EN 62305-3)
Roofs are used as areas for technical equipment. Especially is used (Figure 5.1.11.2).
when extending the technical equipment in the building, ex- With the rolling sphere method, a rolling sphere whose radius
tensive installations are sited on the roofs of large office and depends on the class of LPS selected is rolled in all possible
industrial buildings. In this case, it is essential to protect the directions on and over the structure to be protected. During
different roof-mounted structures such as air-conditioning and this procedure, the rolling sphere may only touch the ground
cooling systems, antennas of cell sites on rented buildings, (reference plane) and / or the air-termination system.

mesh size M
air-termination rod
down conductor
protective angle

Max. height of the building h 2 α rolling sphere
Class Radius of the Mesh r
of LPS rolling sphere (r) size (M)
I 20 m 5 x 5 m
h 1
II 30 m 10 x 10 m
III 45 m 15 x 15 m
IV 60 m 20 x 20 m

earth-termination
system

Figure 5.1.11.2 Procedure for installing air-termination systems according to IEC 62305-3 (EN 62305-3)

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