IT Baseline Protection Manual - The Information Warfare Site

Safeguard Catalogue Infrastucture Remarks
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S 1.25 Overvoltage protection
Initiation responsibility: Head of Site/Bldg Technical Service; Head of
IT Section; IT Security Management
Implementation responsibility: Head of Site/Bldg Technical Service;
administrator
Depending on the quality and advancement of the external power supply
network and the in-house power network, overvoltage peaks can, depending
on the environment (other power consumers) and on the geographical
location, be caused in the supply mains by induction or lightning. As a rule,
overvoltage due to lightning has quite a destructive potential, whilst that of
overvoltage due to other causes is only minor. However, all types of
overvoltage can destroy IT systems.
A comprehensive overvoltage protection policy covers three stages:
- elementary protection in the building feeder;
- medium protection in storey distributors; and
- fine protection provided at the respective sockets and the plug-in
connections of all other lines.
The design of elementary protection depends on the existence of external
lightning arrester. The protective effect of every stage builds on the preceding
stage. If one stage is left out, overvoltage protection will, in its entirety,
become nearly ineffective.
If overvoltage protection cannot be ensured throughout the building, it will at
least be necessary to establish an adequate protective perimeter around
important IT facilities (server, etc.). In order to minimise potential damage,
networks to which multiple devices are connected can, by means of
optocouplers or surge arresters, be divided into small sectors protected from
each other.
Irrespective of the extent and development of overvoltage protection, attention
must be given to two basic requirements:
- The line between the fine-protection feature and the devices to be protected
should not be longer than 20 metres. If that length is exceeded, another
fine-protection device must be interposed. If a device is provided with fine
protection at the entry point, the 20 m limitation does not apply.
- If overvoltage protection is to be effective, comprehensive potential
equalisation is required for all electric resources covered by overvoltage
protection!
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IT-Baseline Protection Manual: Oktober 2000