Page 73 - 35_DS702_E_2014_Lightning_Protection_Guide

If a building has a steel frame construction with a metal roof
s 1 , s 2 separation distance according to horizontal and façade made of conductive material, these parts can be
IEC 62305-3 (EN 62305-3) used for the external lightning protection system, under cer-
air-termination
conductor tain circumstances.
Sheet metal claddings at or on top of the building to be pro-
tected can be used if the electrical connection between the
s 1
different parts is permanent. These permanent electrical con-
nections can be made by e.g. soldering, welding, pressing,
s 2 s 2
air-termi- protected air-termi- screwing or riveting. Qualified persons may also establish con-
nation mast structure nation mast nections by means of soft-soldering. The continuously soldered
2
surface of the connection must be at least 10 cm with a width
reference plane of at least 5 mm.
If there is no electrical connection, these elements must be ad-
Figure 5.1.1.21 Isolated external lightning protection system ditionally connected e.g. by means of bridging braids or bridg-
consisting of two separate air-termination masts ing cables.
connected by a horizontal air-termination conduc- If the thickness of the sheet metal is not less than the value t'
tor: Projection on a vertical surface via the two
masts (vertical section) in Table 5.1.1.5 and if melting of the sheets at the point of
strike or the ignition of flammable material under the clad-
ding does not have to be taken into account, such sheets can
a
Class Material Thickness Thickness be used as an air-termination system. The material thicknesses
b
of LPS t [mm] t' [mm] are not distinguished according to the class of LPS.
If it is, however, necessary to take precautionary measures
Lead – 2.0
against melting or intolerable heating at the point of strike,
Steel (stainless, 4 0.5 the thickness of the sheet metal must not be less than value t
galvanised) in Table 5.1.1.5.
I to IV Titanium 4 0.5
Copper 5 0.5 The required thicknesses t of the materials can generally not
be complied with, for example, in case of metal roofs.
Aluminium 7 0.65 For pipes or containers, however, it is possible to comply with
Zinc – 0.7 these minimum thicknesses (wall thicknesses). If, though, the
temperature rise (heating) on the inside of the pipe or tank
a t prevents puncture
b t` only for sheet metal if puncture, overheating and ignition represents a hazard for the medium contained therein (risk of
does not have to be prevented fire or explosion), these must not be used as air-termination
systems (see also chapter 5.1.4).
Table 5.1.1.5 Minimum thickness of sheet metal
If the requirements concerning the appropriate minimum
thickness are not met, the components, e.g. pipes or contain-
fibre reinforced plastic) to secure the air-termination systems ers, must be situated in an area protected from direct lightning
(air-termination rods, conductors or cables) at the object to be strikes.
protected.
This form of isolation can be limited to local use or applied to A thin coat of paint, 1 mm bitumen or 0.5 mm PVC, cannot be
whole parts of the installation. It is often used for roof-mount- regarded as insulation in the event of a direct lightning strike.
ed structures such as ventilation systems or heat exchangers Such coatings are punctured when subjected to the high ener-
gies deposited during a direct lightning strike.
which have an electrically conductive connection into the
building (see also chapter 5.1.8).
If conductive parts are located on the surface of the roof, they
can be used as a natural air-termination system if there is no
Natural components of air-termination systems conductive connection into the building.
Metal structural parts such as roof parapets, gutters, railings By connecting e.g. pipes or incoming electrical conductors,
or claddings can be used as natural components of an air- partial lightning currents can enter the structure and interfere
termination system. with or even destroy sensitive electrical / electronic equipment.

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