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motor
24 V d.c. < 4 A protective angle α wind / rain sensor

smoke detector
No. Surge protective device Part No.
DG M TN 275 (TN-S system) 952 200
fire control DG M TT 2 P 275 (TT system) 952 110
panel
3* BXT ML4 BE 24 920 324
2*
4* + BXT BAS 920 300
2 x BXT ML4 BE 24 920 324
230 V / 50 Hz + 2 x BXT BAS 920 300
BXT ML4 BE 36 (1.8 A) 920 336
+ BXT BAS or 920 300
6* 4* (6*) 2 x BVT ALD 36 (4 A) 918 408
BXT ML2 BE S 24 920 224
SDS VS + BXT BAS 920 300

=

6*
4* (6*)
Alternative
SDS VS TL2 10DA CC 907 991
DRL 10 B 180 FSD 907 401
EF 10 DRL 907 498
8 x DRL RE 24 907 422
* Minimum number of required cores
(observe manufacturers’ instructions)
Figure 9.27.2 Domelight located in the protected volume of an air-termination rod on a metal roof of a structure with metal down conductor
(steel frame, interconnected reinforced concrete or earthed metal facade)

installed in this zone (Figure 9.27.1). A surge arrester pre- be interconnected by means of lightning current carrying
vents inductive coupling in this zone. conductors if there is no other lightning current carrying
connection (e.g. by means of tested terminals, brazing,
Structure with metal roof and external lightning welding, squeezing, seaming, screwing or riveting).
protection system 3. The metal roof has the required thickness t (IEC 62305-3
In contrast to structures with non-metal roofs and external (EN 62305-3), Table 3)
lightning protection system, different normative require-
ments are placed on the lightning current carrying capability There are two types of down conductors for the metal roofs
of metal roofs which are used as air-termination system: described before:
1. The metal roof can be used as natural air-termination A. The walls consist of an interconnected lightning current
system if the manufacturer confirms that it suited for this carrying steel reinforcement or a steel frame construc-
purpose (DIN EN 62305-3, Supplement 4). tion. In both cases, the separation distance does not have
2. The metal roof does not have the required thickness t’ to be considered since either the current is very low due
(IEC 62305-3 (EN 62305-3 ), Table 3) and must be pro- to the high number of current paths (reinforcements) or
tected against direct lightning strikes by means of air- the low inductance (steel beams) does not cause punc-
termination systems since perforation can cause fire due ture to other metal systems. Metal façades which are
to the highly flammable materials (or wooden boards) connected to the earth-termination system at intervals of
underneath the tin roof and the ingress of water can no 15 m at the lowest point (ground) also meet the require-
longer be prevented. The air-termination systems must ments described above.

412 LIGHTNING PROTECTION GUIDE www.dehn-international.com