Page 10 - Advanced Course

KNX ADVANCED COURSE

A failure of switch actuator 1 or 2 would mean that it would not be possible to switch any
loads throughout the room. It is advisable to select the following assignment if you have
the actuators available:

Switch actuator 1 Channel A Room 1 Light strip at door

Switch actuator 2 Channel A Room 1 Light strip at window

Switch actuator 1 Channel B Room 2 Light strip at door

Switch actuator 2 Channel B Room 2 Light strip at window

etc.

Should one of the two actuators now have a malfunction, both rooms are indeed affected
but at least one light strip would continue to operate per room.

3.4 Benefits of Line Couplers

The higher the number of line couplers that are installed in a system, the better the
structure and fault tolerance of the entire system. The filter tables must however be
commissioned properly to reduce the total number of telegrams in the KNX system, avoid
repeat telegrams and to guarantee the quickest possible transfer of information.
Fail-safe planning is considerably improved by the electrical isolation of both line
segments by a line coupler. Short circuits, overvoltage and other malfunctions can thus
be limited to a line segment. To avoid the build up of telegrams via controllers (telegrams
circulating via logic modules due to faulty programming) or repeat telegrams, the filter
tables should be loaded correctly into the couplers and configured.

3.5 Power Supply

A 640 mA power supply offers the opportunity in most cases to supply more than one line
segment with power. It must however be noted that 2 line segments can no longer be
operated if this power supply fails.

3.6 Power Supply in event of a Power Failure

There are two options for guaranteeing the operation of a line segment for a certain
period without a 230 V supply. Power supply units are available with a battery connection
which can buffer the KNX system for a certain period even after a total power failure. If a
12 V battery is used, it is moreover possible to control an alarm siren with a strobe light
via a switch actuator with floating contacts (see the chapter on “Security technology”).
In certain cases, many bus devices require a separate power supply. These include built-
in panels, PCs with a visualisation system running on them or telephone dialling devices
which are connected to telecommunication systems. The request is often made to enable
signals to be sent even after a failure of the 230 V supply. The supply voltage for the KNX
power supply can be connected e.g. via a UPS – Uninterruptible Power Supply. This
device ensures that the KNX installation continues to function for a certain period after a
mains failure. Other 230 V devices can of course also be connected via the UPS such as

Home and Building Management Systems KNX Association
Fail-safe planning Fail-safe planning_E0206b.doc 10/11