Wiring
6.3 Operation on grounded infeed
Automation system
System Manual, 12/2017, A5E03461182-AE
129
Safe galvanic isolation (SELV/PELV in accordance with IEC 60364-4-41)
Load current supplies/system power supplies with 24 V DC supply require safe electrical
separation. This protection is designated as SELV (Safety Extra Low Voltage)/PELV
(Protective Extra Low Voltage) in accordance with IEC 60364-4-41.
The wiring of SELV/PELV circuits must be separated from the wiring of other circuits that are
not SELV/PELV, or the insulation of all conductors must be rated 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 131).
Short-circuit and overload protection
Various measures as protection against short-circuits and overloads are required for setting
up a full installation. The nature of the components and the degree to which the required
measures are binding depends on the IEC (DIN VDE) regulation applicable to your plant
configuration. The table refers to the following figure and compares the IEC (DIN VDE)
regulations.
Table 6- 1
Components and required measures
Reference to follow-
ing figure
IEC 60364
(DIN VDE 0100)
IEC 60204
(DIN VDE 0113)
Shut-off device for control system, sen-
sors, and actuators
①
Main switch
Disconnector
Short-circuit and overload protection:
In groups for sensors and actuators
②
③
Single-pole protection of
circuits
•
With grounded sec-
ondary circuit: fuse
unipolar
•
Otherwise: fuse all
poles
Load current supply for AC load circuits
with more than five electromagnetic de-
vices
④
Galvanic isolation by
transformer recommended
Galvanic isolation by
transformer recommended
Summary of Contents for Simatic S7-1500/ET 200MP
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