Siemens Simatic S7-300 CPU 31xC Series - Modules with Isolated or Common Potential

Configuring
4.9 Electrical assembly, protective measures and grounding
S7-300, CPU 31xC and CPU 31x: Installation
Operating Instructions, Edition 08/2004, A5E00105492-05
4-19
4.9.4 Modules with isolated or common potential?
Isolated modules
Isolated modules are installed with galvanic isolation between the reference potentials of the
control circuit (M
internal
) and load circuit (M
external
.)
Field of application
Use isolated modules for:
• All AC load circuits
• DC load circuits with separate reference potential
Examples:
– DC load circuits containing sensors which are connected to different reference
potentials (for example, if grounded sensors are located at a considerable distance
from the control system and equipotential bonding is not possible)
– DC load circuits with grounded positive pole (L+) (battery circuits.)
Isolated modules and grounding concept
You can always use isolated modules, irrespective of the grounding state of the control
system's reference potential.