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control unit

con-
troller
power supply

temperature
sensor
heating cable

moisture sensor

Type Part No.
DG M TT 2P 275 (TT/TN-S system) 952 110
DG M TT 275 (TT/TN-S system) 952 310
BXT ML2 BE S 5 920 220
+ BXT BAS 920 300
DSH TT 2P 255 (TT/TN-S system) 941 110
DSH TN 255 (TN-S system) 941 200

Figure 9.29.2 Installation of lightning current and surge arresters if the control unit is located far from the entry point into a structure with
external lightning protection system

splits both between the down conductors directly connected tion. If the air-termination systems ensure that the cables be-
to the metallic gutter and the down conductors connected to yond the roof are not hit by a lightning strike, surge protective
the air-termination mesh. Even if the external lightning protec- devices according to Figure 9.29.1 can be used.
tion system only has four down conductors, lightning currents
of less than 10 to 12 kA per core are to be expected in case of If loss of the control unit is acceptable (the control unit and / or
LPL III. A type 2 surge arrester must be provided in the feeder the incoming cables must not present a risk of fire), the struc-
cable upstream of the control unit (Figure 9.29.2). ture can be protected by installing combined arresters directly
at the point where the cables enter the structure (Figure
Buildings with an interconnected reinforced concrete or steel 9.29.3).
frame construction (IEC 62305-4 (EN 62305-4)) are an excep-

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