IT Baseline Protection Manual - The Information Warfare Site

Safeguard Catalogue Infrastucture Remarks
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S 1.28 Local uninterruptable power supply (ups)
Initiation responsibility: Head of Site/Bldg Technical Service; Head of
IT Section; IT Security Management
Implementation responsibility: Head of Site/Bldg Technical Service;
administrator
With an uninterruptable power supply (UPS), it is possible to bridge a shortterm
power failure or maintain the power supply long enough to allow an
orderly shut-down of the connected computers. This is particularly expedient
- when large quantities of data are stored temporarily in the computer (e.g.
cache memory in the network server) before their transfer to non-volatile
storage;
- if, in case of power failure, large quantities of data would be lost and their
subsequent re-entry would be required;
- if the stability of power supply is not sufficiently ensured.
Two types of UPS should be distinguished:
- Offline UPS: The connected power consumers are normally fed directly
from the supply mains. It is only in the case of failure of the latter that the
UPS will automatically switch in and take over the supply function.
- Online UPS: The UPS is permanently switched between the mains and the
power consumers. The entire power supply is always provided through the
UPS.
In addition to tiding over a complete breakdown of power supply and
undervoltage situations, both types of UPS can also serve to smooth
overvoltage. In this case, too, the 20 m limit specified in S 1.25 Overvoltage
Protection applies with regard to overvoltage protection.
If IT equipment in a building with TN-S network (see S 1.39 Prevention of
transient current on shielding) is supplied by a local UPS, the following
should be observed: In order to maintain the protective effect of the TN-S
network against transient current on shielding of data lines, the PE conductor
of the power line must not be connected to the PE conductor of the output side
of the UPS.
When dimensioning a UPS system, a normal by-pass time of about 10 to 15
minutes can, as a rule, be assumed. In most cases, a power failure will be
remedied within 5 to 10 minutes. This leaves about 5 minutes for the orderly
shut-down of the connected IT systems if the power failure should persist for
some time. Most modern UPS equipment offers computer interfaces capable
of initiating a timely automatic shut-down after a predefined time, in accordance
with the time requirements of the IT systems and the capacity of the
UPS.
For specific applications (e.g. PBX), the necessary by-pass time may be
several hours.
In order to preserve the protective effect, provisions must be made for regular
maintenance of the UPS system.
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IT-Baseline Protection Manual: Oktober 2000