Siemens SIMATIC S5-100U System Manual page 65

S5-100U
When you have a non-floating configuration, you must make certain that the voltage drop on
cables and does not exceed 1 V. If 1 V is exceeded, the reference potentials could change
and the modules could malfunction.
Warning
If you use non-floating I/O modules, you must provide an external connection between
the chassis ground of the non-floating I/O module and the chassis ground of the CPU.
Example of a Floating Configuration with Digital Modules
Floating configuration is required in the following situations.
• When you need to increase interference immunity in the load circuits
• When load circuits cannot be interconnected
• When you have AC load circuits
If you have a floating configuration, the PLC's control circuit and the load circuit must be galvanically
isolated.
Figure 3-23 shows a simplified connection of galvanically isolated I/Os.
Central
grounding point
L+
Load power
supply
Figure 3-23. Simplified Representation of a Galvanically Isolated Connection of the
I/Os to the S5-100U
EWA 4NEB 812 6120-02b
PS CPU
L+
M
M
Installation Guidelines
3-27