Siemens Simatic S7-300 CPU 31xC Series Installation And Operating Instructions Manual page 104

Wiring
6.4 Wiring the power supply module and the CPU
6. Close the front panels.
The figure below illustrates the procedures described earlier.
1
Key to numbers in the figure
(1)
(2)
(3)
Note
The PS 307 power supply module is equipped with two additional 24 VDC terminals L+ and
M for the supply to I/O modules.
6-6
Warning
Reversing the polarity of the M and L+ terminals trips the internal fuse on your CPU.
Always interconnect the M and L+ terminals of the power supply module and of the CPU.
I
L1
N
L+
M
L+
L+
M
M
230V/120V
2
Strain relief of the power supply cable
Connection cables between the PS and CPU
Removable power supply connector
3
Operating Instructions, Edition 08/2004, A5E00105492-05
S7-300, CPU 31xC and CPU 31x: Installation