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The separation distance s between the air-termination and
45 m down-conductor systems and the structure must be main-
metal capping of tained. If the air-termination system consists of one or more
15 m the roof parapet spanned wires or cables, each cable end on which the conduc-
courtyard tors are fixed requires at least one down conductor (Figure
circumference 5.2.3.2).
7.5 m > 30 m courtyards with a cir- If the air-termination system forms an intermeshed network
30 m cumference of more of conductors, i.e. the individual spanned wires or cables are
than 30 m, typical
distances according interconnected to form a mesh (cross-linked), there must be
at least one down conductor on each cable end on which the
to class of LPS
conductors are fixed (Figure 5.2.3.3).
Figure 5.2.2.5.1 Down-conductor systems for courtyards
5.2.4 High voltage-resistant, insulated down
The effects of partial lightning currents flowing through inter- conductor – HVI Conductor
nal down conductors within the structure must be taken into
account. When designing the internal lightning protection The main function of an external lightning protection system
system, the resulting electromagnetic field in the vicinity of is to intercept a lightning strike according to the principle of
the down conductors must be considered (observe injection to Benjamin Franklin, discharge it along the building and safely
conduct it to the ground. To prevent dangerous flashover be-
electrical / electronic systems).
tween the parts of the external lightning protection system
and conductive parts inside the structure (electrical / electronic
equipment, pipes, ventilation ducts, etc.) resulting from a di-
5.2.2.5 Courtyards rect lightning strike, it is imperative to maintain the separation
Structures with enclosed courtyards with a perimeter of more distance s when designing and installing a lightning protection
than 30 m require down conductors with the distances shown system.
in Table 5.2.1.1 (Figure 5.2.2.5.1). The separation distance s is calculated according to section 6.3
of the IEC 62305-3 (EN 62305-3) standard.

5.2.3 Down conductors of an isolated exter- However, it is often impractical to keep the separation distance
nal lightning protection system in new and existing structures. For aesthetic reasons, modern
architecture often does not allow to use GRP spacers to lead
If an air-termination system consists of air-termination rods the down conductor to the ground. In modern industrial plants,
on isolated masts (or one mast), they assume the function of the roof is often the last installation level for equipment such
an air-termination system and down conductor system at the as ventilation and air-conditioning systems, antennas, differ-
same time (Figure 5.2.3.1). Each individual mast must be fit- ent pipe systems and cable ladders. In this context, it is im-
ted with at least one down conductor. Steel masts or masts perative to observe lightning protection systems and maintain
with interconnected reinforcing steel require no additional the necessary separation distances. Direct lightning strikes
down conductors. For aesthetic reasons, a metal flag pole, for to structures protruding above the roof can be prevented if
example, can also be used as an air-termination system. air-termination systems dimensioned according to the rolling

s s mechanical fixing
s

down
conductor

Figure 5.2.3.1 Air-termination masts isolated Figure 5.2.3.2 Air-termination masts Figure 5.2.3.3 Air-termination masts spanned
from the building spanned with cables with cross-linked cables
(meshes)

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