Wiring
7.3 Operation on grounded infeed
Automation system
System Manual, 01/2023, A5E03461182-AK
155
Safe electrical isolation (SELV in accordance with IEC 61131-2 or IEC 61010-2-201)
Load power supplies/system power supplies with a 24 V DC output voltage require safe
electrical isolation and a voltage limit (extra low voltage). Load power supplies/system power
supplies with a 24 V DC output voltage are not connected to the protective conductor.
In accordance with IEC 61131-2 / IEC 61010-2-201, this protection is referred to as SELV
(Safety Extra Low Voltage).
Either the wiring of SELV circuits must be safely isolated from the wiring of other circuits that
are not SELV, or the insulation of all wires must be dimensioned for the higher voltage.
Protective extra-low voltage (PELV in accordance with IEC 61131-2 or IEC 61010-2-201)
Load power supplies/system power supplies with a protective 24 V DC output voltage require
a safe connection to the protective conductor and a voltage limit (extra low voltage).
In accordance with IEC 61131-2 / IEC 61010-2-201, this protection is referred to as PELV
(Protective Extra Low Voltage).
Either the wiring of PELV circuits must be safely isolated from the wiring of other circuits that
are not PELV, or the insulation of all wires must be dimensioned for the higher voltage.
Reference potential of the controller
The reference potential of the S7-1500 automation system/ ET 200MP distributed I/O system
is connected with the mounting rail through a high-resistance RC combination in the
CPU/interface module. In this way, high-frequency interference currents are conducted and
electrostatic charges are avoided. Despite the grounded mounting rail, the reference
potential of the S7-1500 automation system / ET 200MP distributed I/O system has to be
considered as ungrounded due to the high-resistance connection.
If you want to configure the S7-1500 automation system/ET 200MP distributed I/O system
with grounded reference potential, connect the M connection of the CPU/interface module
galvanically with the protective conductor.
You can find a simplified representation of the potential relationships in section Electrical
configuration (Page 158).
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