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Solar radiation and waste heat from buildings may melt ice Since both the heating bands and the temperature and mois-
or snow even under frost conditions. Such melt water then re- ture sensor are located outside the structure, their connect-
freezes, preventing water from draining away and causing it ing cables are exposed to inductive coupling which may cause
to back up. As a result, the roof drainage is blocked and icicles damage to the structure. For this reason, type 2 surge arresters
may form which involves an increased risk. are installed to protect these cables directly at the entry point
into the structure and the feeder cable upstream of the control
An even more serious problem is a heavy snow and ice build unit (Figure 9.29.1).
up on the roof that may exceed the maximum load capacity
of the roof. Structure with external lightning protection system
Gutter heating systems prevent damage provided that their The IEC 62305-1 to 4 (EN 62305-1 to 4) standard must be ob-
reliable function is ensured even under lightning and surge served when installing lightning protection systems on struc-
conditions. tures. In such systems, the gutters and / or downpipes are typi-
cally conductively connected to the air-termination systems and
Structure without external lightning protection are therefore at a high potential in case of a lightning strike.
system Both the heating band and moisture sensor cables directly con-
If a structure has no external lightning protection system, it tact these lightning current carrying gutters and downpipes,
can be assumed that the operator considers the probability of meaning that lightning currents are automatically injected on
lightning striking the structure to be low. In this case, type 2 the cables. For this reason, type 1 lightning current arresters
surge arresters according to IEC 60364-1 (HD 60364-1) must must be installed directly at the point where the cables enter
be used to protect the structure from inductive coupling. the structure. It must be observed that the lightning current

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

Figure 9.29.1 Control unit protected by surge arresters in a structure without external lightning protection system

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