Siemens SIMATIC ET 200AL, System Manual

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Connecting
5.2 Additional rules and regulations for the operation of the ET 200AL with fail-safe modules
Distributed I/O system
System Manual, 08/2021, A5E31861578-AJ
35
5.2 Additional rules and regulations for the operation of the
ET 200AL with fail-safe modules
5.2.1 Safety extra-low-voltage (SELV, PELV) for fail-safe modules
WARNING
The fail-safe modules must be operated with a safe extra-low voltage (SELV, PELV).
You can find additional information on safety extra-low voltage (SELV, PELV) in the data
sheets of the applicable power supplies, for example.
The fail-safe modules operate at a rated voltage of 24 V DC. The tolerance range is
20.4 V DC to 28.8 V DC.
Within the overvoltage range from 28.8 V DC to 35 V DC, the F-modules react in a fail-safe
manner and the inputs and outputs are passivated. For overvoltages higher than 35 V DC,
the F-modules are permanently de-energized.
Use a power supply unit that does not exceed U
m
= 35 V DC even in the event of a fault. For
more on this, refer to the information in the data sheet on overvoltage protection in the
case of an internal error. Or implement appropriate measures to limit the voltage, e.g. use
of an overvoltage protector.
All system components that can supply electrical energy in any form whatsoever must fulfill
this condition.
Each additional circuit (24 V DC) used in the system must have a safety extra-low voltage
(SELV, PELV). Refer to the relevant data sheets or contact the manufacturer.
Sensors and actuators with an external power supply can also be connected to F-modules.
Make sure that power is supplied to these components from safety extra-low voltage (SELV,
PELV) as well. The process signal of a 24 V DC digital module must not exceed a fault
voltage U
m
in the event of a fault.
WARNING
Even when a fault occurs, the permissible potential difference between the supply of the
interface module (bus voltage) and the load voltage must not be exceeded.
An external direct electrical connection is one way to meet this requirement. This also
prevents potential differences from causing voltage additions at the individual voltage
sources, which would cause the fault voltage U
m
to be exceeded.
Immunity to surge voltages
To meet the product standard for burner controls (EN 298), the wiring must be equipped
with external protection against coupled surge voltages caused by lightning. Further
information on this can be found in the function manual Designing interference-free
controllers ( https://support.industry.siemens.com/cs/ww/en/view/59193566 ).