Installing
3.3 Terminal blocks
CU250S-2 Control Units
Compact Operating Instructions, 05/2014, A5E32899990B AB
11
Optional 24 V supply (terminals 31, 32)
Connection of the optional 24 V supply has the following advantages:
● The Control Unit remains in operation after disconnection of the Power Module from the
line supply. The Control Unit thus maintains the fieldbus communication, for example.
● You can use terminals 51 … 54 as digital outputs.
Use a power supply that provides an output voltage in accordance with SELV (Safety Extra
Low Voltage) or PELV (Protective Extra Low Voltage).
If you use a common external power supply for terminals 31, 32 and the digital inputs, you
must connect GND to GND IN.
Terminal strips behind the lower front door
Different reference potentials:
The reference potentials of the digital inputs are not connected internally to each other or to GND.
Figure 3-2 Interconnection example of the digital inputs with external 24 V power supplies
Interconnecting the reference potential of the digital inputs
Table 3- 2 Supply options for the digital inputs
Reference potential interconnection
You are using an external 24 V supply Connect the reference potential of the external 24 V supply
to the reference potential of the appropriate digital input.
You are using the internal 24 V supply
Connect the appropriate reference potential of the digital
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