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current and resulting from the connection to the lightning pro- Test joints are required to facilitate the inspection of the fol-
tection system must be observed. lowing characteristics of the lightning protection system:
¨ Connections of the down conductors via the air-termina-
Connections to prestressing bars or cables must only be ef- tion systems to the next down conductor
fected outside the stressed area. The permission of the installer
of the structure must be given before using prestressing bars ¨ Interconnections of the terminal lugs via the earth-termi-
or cables as a down conductor. nation system, e.g. in case of ring or foundation earth elec-
If the reinforcement of existing structures is not safely inter- trodes (type B earth electrodes)
connected, it cannot be used as a down conductor. In this case, ¨ Earth resistances of single earth electrodes (type A earth
external down conductors must be installed. electrodes)
Furthermore, façade elements, DIN rails and metal sub-struc-
tures of façades can be used as a natural down conductor pro- Test joints are not required if the structural design (e.g. rein-
vided that: forced concrete or steel frame structure) allows no electrical
¨ The dimensions meet the minimum requirements for down isolation of the natural down conductor from the earth-termi-
conductors. For sheet metal, the thickness must not be less nation system (e.g. foundation earth electrode). The test joint
than 0.5 mm. Their electrical conductivity in the vertical di- may only be opened with the help of a tool for measurement
rection must be ensured. If metal façades are used as a purposes, otherwise it must be closed. Each test joint must be
down conductor, they must be interconnected to ensure clearly identifiable in the plan of the lightning protection sys-
that the individual sheet metal plates are safely intercon- tem. Typically, all test joints are marked with numbers (Figure
nected by means of screws, rivets or bridging connections. 5.2.2.3.1).
There must be a safe current carrying connection to the
air-termination and earth-termination system.
5.2.2.4 Internal down conductors
¨ If sheet metal plates are not interconnected in accordance
with the above requirement, but the substructure is such If the edges of the building (length and width) are four times
that they are continuously conductive from the connec- as large as the distance of the down conductors according to
tion to the air-termination system to the connection on the the class of LPS, supplementary internal down conductors must
earth-termination system, they can be used as a down con- be installed (Figure 5.2.2.4.1). The grid dimensions for the
ductor (Figures 5.2.2.2.2 and 5.2.2.2.3). internal down conductors are about 40 m x 40 m.
Large flat-roofed structures such as large production halls or dis-
Metal downpipes can be used as natural down conductors tribution centres frequently require internal down conductors. In
as long as they are safely interconnected (soldered or riveted such cases, the ducts through the surface of the roof should be
joints) and have a minimum wall thickness of 0.5 mm (Figure installed by a roofer since he is responsible for rain safety.
5.2.2.1.2).
If a downpipe is not safely intercon- roof bushing
nected, it can be used as a holder for
the supplementary down conductor. roofing separation
This type of application is illustrated in heat insulation distance s
Figure 5.2.2.2.4. The downpipe must timber formwork
be connected to the earth-termination
system in such a way that it can carry
lightning currents since the conductor is internal down
only connected to the pipe. conductor

metal structure
5.2.2.3 Test joints
A test joint must be provided at every If the separation distance is too small, the conductive parts of the building
connection of a down conductor to the structure must be connected to the air-termination system. The effects
earth-termination system (above the of the currents must be taken into account.
earth entry, if practicable). Figure 5.2.2.4.1 Air-termination system for large roofs – Internal down conductors

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