Siemens Simatic S7-300 CPU 31xC Series Installation And Operating Instructions Manual page 44

Configuring
4.9 Electrical assembly, protective measures and grounding
Example: Assembly with CPU 31xC and isolated modules
The figure below shows an example of such a configuration: A CPU 31xC with isolated
modules. The CPU 31xC (1) is automatically grounded.
L1
N
PE
Common grounding
line in the cabinet
L +
M
external
24 V DC load power supply
Common potential modules
In a configuration containing modules with common potential, the reference potentials of the
control circuit (M
4-20
S7-300 CPU
PS
1
µ P
L1
L +
M
N
) and analog circuit (M
internal
DO
DI
230 V AC
load power supply
) are not galvanically isolated.
analog
S7-300, CPU 31xC and CPU 31x: Installation
Operating Instructions, Edition 08/2004, A5E00105492-05
U
internal
Data
M
internal
L1
N