Power Budget - Siemens S7-1200 System Manual

3.2

Power budget

Your CPU has an internal power supply that provides power for the CPU, the signal
modules, signal board and communication modules and for other 24 VDC user power
requirements.
Refer to the technical specifications (Page 829) for information about the 5 VDC logic budget
supplied by your CPU and the 5 VDC power requirements of the signal modules, signal
boards, and communication modules. Refer to the "Calculating a power budget" (Page 985)
to determine how much power (or current) the CPU can provide for your configuration.
The CPU provides a 24 VDC sensor supply that can supply 24 VDC for input points, for relay
coil power on the signal modules, or for other requirements. If your 24 VDC power
requirements exceed the budget of the sensor supply, then you must add an external
24 VDC power supply to your system. Refer to the technical specifications (Page 829) for the
24 VDC sensor supply power budget for your particular CPU.
Note
The CM 1243-5 (PROFIBUS master module) requires power from the 24 VDC sensor supply
of the CPU.
If you require an external 24 VDC power supply, ensure that the power supply is not
connected in parallel with the sensor supply of the CPU. For improved electrical noise
protection, it is recommended that the commons (M) of the different power supplies be
connected.
Connecting an external 24 VDC power supply in parallel with the 24 VDC sensor supply
can result in a conflict between the two supplies as each seeks to establish its own
preferred output voltage level
The result of this conflict can be shortened lifetime or immediate failure of one or both
power supplies, with consequent unpredictable operation of the PLC system. Unpredictable
operation could result in death, severe personal injury and/or property damage.
The DC sensor supply and any external power supply should provide power to different
points.
S7-1200 Programmable controller
System Manual, 03/2014, A5E02486680-AG
WARNING
Installation
3.2 Power budget
51