In the event of short-circuits at digital outputs, if the load power
supply is not adequately rated, a current which is higher than the rated
current can flow for a longer period without responding of the
electronic short-circuit protection of the DQ module. Operation in the
overload region can destroy the module.
Load power supply for
non-floating modules
If you use non-floating modules, you must create a common reference
potential for the internal control circuits of the PLC and for the load
circuits. The reference potential of the load power supply should
therefore be connected to the ground terminal of the PLC (PE or
protective conductor terminal). The ground terminal is permanently
connected to the internal reference potential of the controller.
Load power supply for
floating modules
Note
If you use switched-mode power supply units for floating analog
modules and BEROs, you must fit an AC system filter to the input
of the power supply.
3.4.2
Connecting the
Programmable Controller
and Load Power Supply
Each of the following figures shows a circuit example for connecting
the control and load power supplies as well as the grounding concept
for operation from:
••
Grounded supplies
••
Centrally grounded supplies
••
Ungrounded supplies
When assembling the control system, observe the following
explanations. The text contains identification numbers relating to
Figures 3-8 to 3-10.
Main switch and protection
••
For the programmable controller, sensors and actuators, you must
fit a main switch
➀
to DIN VDE 0113, Part 1, or an isolating
device to DIN VDE 0100, Part 460. If an AC plug is used as the
isolating device, the socket must be in the vicinity of the CC and
must be easily accessible (VDE 0805, 1.7.2). These devices are not
required in the case of a subsystem where the appropriate devices
are fitted at a higher level.
••
The circuits for sensors and actuators can be given group
protection for short-circuit and/or overload
➁
. According to
VDE 0100, Part 725, single-phase protection is required; and
all-phase protection to DIN VDE 0113, Part 1.
3
Power Supplies for Programmable Controllers and I/Os
System Manual
C79000-B8576-C199-03
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