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Building Technologies
Basic documentation: Communication via the KNX bus
CE1P3127en
HVAC Products
Engineering notes
30.08.2007
The rule is: One device with a DPSU can operate two devices without a bus power
supply plus the OCI700 service interface and OZW771 central communication unit.
Per line, the rule is:
1 device with a DPSU + 2 devices with no bus power OZW771
up to a maximum of
8 devices with a DPSU + 16 devices with no bus power + OZW771
An RM… controller with a DPSU delivers a net current of 25 mA. This covers the
power consumption of 5 devices without a bus power supply (5 mA each required).
8 devices with a DPSU on one line deliver 200 mA. This covers the power con-
sumption for 40 devices or 38 devices plus OCI700 plus OZW771.
Even with devices having a low current requirement (< 3 mA), the number of
devices in a line must not exceed 64.
Refer to the data sheets for the power consumption of the new Synco devices.
2.2.2 Power
consumption of the bus devices
To optimize the connectable devices set to "Decentral bus power supply = Off" and
the devices without a bus power supply, it is necessary to calculate the power con-
sumption from the KNX bus.
Power consumption values for Synco devices with "Bus power supply = Off":
•
RMU7x0, RMU7x0B universal controllers
5 mA
•
RMH760, RMH760B heating controllers
5 mA
•
RMK770 boiler sequence controller
5 mA
•
RMB795 central control unit
5 mA
•
RMS705 switching & monitoring device
5 mA
•
OZW775 central communication unit
5 mA
•
QAX910 central apartment unit
5 mA
Power consumption values for Synco devices without a bus power supply:
•
QAW740 room unit
7.5 mA
•
RXB/RXL room controllers
5 mA
•
RMZ792 bus operator unit
45 mA if directly connected to bus
(e.g. via bus socket)
without external power supply
•
RMZ792 bus operator unit
5 mA
if directly connected to bus
with external AC 24 V supply
•
OZW771.xx central communication units
5 mA
Power consumption values for service interface, coupler and IP router:
•
OCI700 service interface
5 mA
•
Area/line coupler N140/13
6 mA
Primary line (main line)
8 mA
Secondary line (sub-line)
•
IP router N146
10 mA
From bus
1)
1)
The Siemens IP router N146 consumes 10 mA from the KNX bus despite the
additional external auxiliary voltage AC/DC 24 V. Power consumption with
auxiliary voltage: 25 mA at DC 24 V, max. 800 mW.
Rule of thumb
Optimization
Notes
