Description:
If the overall power requirement of the S7-300 modules in subrack 0 exceeds the power supply provided by the CPU on the backplane bus, then you must implement interface modules.
The S7-300 CPUs provide 1.2 A for the backplane bus. If this is not sufficient, then you must implement interface modules IM 360 /IM 361. If you implement IM 360 (requires 350 mA itself), then there is only 800 ma left for the 8 possible I/O modules in subrack 0.
Interface modules IM 361 each provide 800 ma for the backplane bus in subracks 1 to 3.

Notes:

• CPUs 312 and 312 C, with which you can only have a single-line setup, provide 800 ma
• IM 365 cannot be used to cover increased power requirements in another subrack, because it can only distribute the power supply provided by the CPU in subrack 0 to subrack 1. IM 365 can distribute max. 800 ma of the power provided by the CPU in subrack 0 to subrack 1. IM 365 itself requires 100 ma from the backplane bus.
   
• You can find more information on this in the manuals:
  • "Programmable Logic Controllers S7-300 Module Data" in Entry ID: 8859629
  • "S7-300, CPU 31xC and CPU 31x: Installation Operating Instructions" in Entry ID 13008499.