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Siemens S5-135U/155U User Manual

Page 53

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3-27

System Manual
C79000-G8576-C199-06

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

S

to prevent energized contactors or relays from being released

S

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

S

for all AC load circuits and

S

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.

1L+

1L–

PE

24 V DC Control Power Supply

2L+

2L–

24 V DC Load Power Supply

PS

CPU

DI

DQ

Data

0 V

U

int

L1

N

230 V AC Load Power Supply

Figure 3-12

Simplified Representation of an Arrangement with Floating Modules

Installation with
Floating Modules

Installation Guidelines