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Building Technologies
Basic documentation: Communication via the KNX bus
CE1P3127en
HVAC Products
Engineering notes
30.08.2007
2.3.1
Distances and cable lengths
The details of distances and cable lengths in a network are designed for bus cables
specified by KNX.
In a KNX network with a "decentral bus power supply unit, DPSU" (see section
2.2.1) the distances between devices depend on the number of devices with a
DPSU.
Maximum distance
Number of
devices with
DPSU
From device
with DPSU
to bus device
From bus device
to bus device
Total length of all
cables in one line
1
350 m
350 m
max. 350 m
2
350 m
700 m
max. 700 m
3 to 8
350 m
700 m
max. 1000 m
There is no minimum distance between devices with a DPSU.
1)
Bus device without a bus power supply unit
In a KNX network with "central bus power supply, PSU" (see section 2.2.2) the
following information on distances must be observed:
•
Distance between two power supply units, PSU
Min. 200 m
•
Distance between bus device and nearest PSU
Max. 350 m
•
Distance between bus devices
Max. 700 m
•
Total length of all cables of one line
Max.1000 m
At least one power supply unit, PSU, is required for each line, and the maximum
per line is two.
The power supply unit should be installed as close to the middle of a line as
possible so that the maximum line length is possible.
The distance between a bus device and the nearest power supply unit must not
exceed 350 meters. Hence:
•
Even if the power consumption of the bus devices does not demand it, two
power supply units may be required, depending on the length of a line, or a
network with several lines and power supply units must be created.
Bus cable: KNX specified
Network with DPSU
Network with PSU
Notes