Siemens SIMATIC S7-1200 System Manual page 1556
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- Function manual (527 pages) ,
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- System manual (338 pages)
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Calculating a power budget
Some of the 24 V DC power input ports in the PLC system are interconnected, with a logic
common circuit connecting multiple M terminals. The CPU 24 V DC power supply input, the
SM relay coil power input, and a non-isolated analog power supply input are examples of
circuits that are interconnected when designated as not isolated in the data sheets. All non-
isolated M terminals must connect to the same external reference potential.
Connecting non-isolated M terminals to different reference potentials will cause unintended
current flows that may cause damage or unpredictable operation in the PLC and connected
equipment.
Such damage or unpredictable operation could result in death, severe personal injury
and/or property damage.
Always be sure that all non-isolated M terminals in a PLC system are connected to the
same reference potential.
Information about the power budgets of the CPUs and the power requirements of the signal
modules is provided in the technical specifications (Page 1359).
Note
Exceeding the power budget of the CPU may result in not being able to connect the
maximum number of modules allowed for your CPU.
Example power budget
The following example shows a sample calculation of the power requirements for a
configuration that includes one CPU 1214C AC/DC/Relay, one SB 1223 2 x 24 V DC Input/ 2
x 24 V DC Output, one CM 1241, three SM 1223 8 DC In/8 Relay Out, and one SM 1221 8
DC In. This example has a total of 48 inputs and 36 outputs.
Note
The CPU has already allocated the power required to drive the internal relay coils. You do
not need to include the internal relay coil power requirements in a power budget calculation.
1556
WARNING
S7-1200 Programmable controller
System Manual, V4.2, 09/2016, A5E02486680-AK
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