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the down conductors of the external lightning protection Arresters for information technology systems must limit
system. conducted interference to an acceptable level so that the
¨ Use of optical fibre cables for the information technology immunity level of the terminal device is not exceeded. For
cables of different buildings (campus backbone cabling) example, an arrester with a lower let-through value than the
EMC test values of the terminal device must be selected for
¨ Installation of surge protective devices in power circuits a terminal device tested with test level 2: Impulse voltage
and for the horizontal cabling system to protect them < 1 kV in combination with an impulse current of some am-
from transients caused by switching operations and light- peres (depending on the type of injection).
ning discharges (Figures 9.11.3 and 9.11.4) Depending on the application and design, the information
¨ Power installation in the form of a TN-S system to prevent technology interfaces of terminal devices have different im-
interference currents on the shields of the data lines munity levels. When selecting an adequate surge arrester,
not only the system parameters are important, but also the
¨ Establishing main equipotential bonding with the power fact whether the arrester is capable of protecting the termi-
installation (PEN) at one point in the building (e.g. service nal device. To ensure easy selection, an SPD class sign was
entrance room) developed for the Yellow/Line product family. Together with
the documentation of the terminal device, this sign provides
To ensure proper EMC protection, it is also important to exact information on whether an arrester is suitable for the
choose adequate lightning current and surge arresters for relevant terminal device, namely whether they are energy-
information technology systems and to be familiar with their coordinated with each other.
protective effect. Correctly dimensioned surge arresters reliably protect termi-
nal devices from voltage and energy peaks, thus increasing
Protective effect of arresters for information tech- the availability of the installation.
nology systems
For testing the electromagnetic compatibility (EMC), electri- Modern communication networks are increasingly becoming
cal and electronic equipment (devices) must have a defined high-frequency networks and thus more and more suscepti-
immunity to conducted interference (surges). ble to interference. Therefore, a consistent EMC concept that
also includes lightning and surge protection for the buildings
Different electromagnetic environmental conditions require and systems is required to ensure smooth network operation
that the devices have different immunity levels. The immunity (Figure 9.11.5).
level of a device depends on the test level. To define the dif-
ferent immunity levels of terminal devices, the test levels are Selection of surge protective devices
subdivided into four different levels from 1 to 4. Test level 1 To ensure effective surge protection, the electricians and IT
places the lowest requirement on the immunity of a terminal experts must coordinate the measures for the different sys-
device. The test level can be usually found in the documenta- tems in cooperation with the manufacturer of the device.
tion of the device or can be requested from the manufacturer
of the device.

Figure 9.11.3 NET Protector – Universal surge protective device for Figure 9.11.4 DEHNprotector – Universal surge protective device
protecting the data lines of a floor distributor (also for protecting the network and data lines of a work
suited for class D networks) station

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