Siemens S5-135U/155U - Manual (Page 46)

3-20
System Manual
C79000-G8576-C199-06
3.4 Power Supplies for Programmable Controllers and I/Os
This section describes:
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Which circuits you must distinguish in the control system and which
demands are made on the power supply.
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Connection and grounding concept with higher-level infeed from
grounded, centrally grounded and ungrounded supplies.
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Connecting the power supply to non-isolated and isolated modules.
3.4.1 Power Supplies for Control Systems with SIMATIC S5
For control systems with SIMATIC S5, you will need:
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A power supply for the internal PLC circuits (control power supply)
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and a load power supply for the input and output circuits.
The power supply for the internal PLC circuits powers the CPU and the
modules used.
Note
Ensure that the control power supply is not overloaded. Make a current
addition and estimate the current drawn by all modules.
The load power supply feeds the input and output circuits (load circuits) as
well as sensors and actuators. Only a power supply which offers safe
electrical isolation from the AC system may be used for the 24 V DC supply.
!
Caution
Only safety-separated low voltage DC
v 60 V may be used for the 24 V DC
supply. The safety separation can be implemented according to the
requirements of, amongst other sources, VDE 0100, Part 410/HD
384-4-41/IEC 364-4-41 (functional extra-low voltage with safety separation)
or VDE 0805/EN 60950/IEC 950 (safety extra-low voltage SELV) or VDE
0106, Part 101.
Power Supply for
the PLC Circuits
Load Power
Supply for the I/Os
Installation Guidelines