Operation On Grounded Infeed - Siemens SIMATIC S7-1500 System Manual

5.3

Operation on grounded infeed

Introduction
Information is provided below on the overall configuration of an S7-1500 automation
system/ET 200MP distributed I/O system on a grounded infeed (TN-S system). The specific
subjects discussed are:
● Disconnecting devices, short-circuit and overload protection to IEC 60364 (corresponding
to DIN VDE 0100) and IEC 60204 (corresponding to DIN VDE 0113)
● Load current supplies and load circuits
Grounded infeed
In the case of grounding incoming supplies (TN-S system) the neutral conductor (N) and the
protective conductor (PE) are each grounded. Both conductors form a part of the overvoltage
concept. When a plant is in operation, the current flows across the neutral conductor. When
a fault occurs, for example a single ground fault between a live conductor and ground, the
current flows through the protective conductor.
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 c ontroller
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 72).
Automation system
System Manual, 09/2016, A5E03461182-AD
5.3 Operation on grounded infeed
Wiring
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