Release - Siemens S5-155U System Manual

Installation with floating
modules
Figure 3-12 Simplified Representation of an Arrangement with Floating Modules
System Manual
C79000-B8576-C199-03
Power Supplies for Programmable Controllers and I/Os
Note
For 24 V DC digital output modules with electronic short-circuit
protection, you must ensure that the reference potential of the load
power supply is connected to terminal L- of the module. If this
connection is missing (e.g. open-circuit), a typical current of
15 mA can flow at the outputs. This output circuit is sufficient
• •
to prevent energized contactors or relays from being released,
• •
and to energize high-resistance loads (e.g. miniature relays).
With floating modules the control circuit and load circuit are
metallically isolated.
An arrangement with floating modules is required
• • for all AC load circuits
and
• • for DC load circuits which cannot be coupled. The reasons are, for
example, different reference potentials of the sensors or grounding
of the positive terminal of a battery.
Shown in the following figure is a simplified installation with floating
modules. The arrangement is independent of the grounding concept.
The connections for grounding are therefore not drawn.
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