Siemens SIMATIC S7-1500 System Manual page 172

Wiring
7.2 Operation on grounded infeed
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).
The wiring of SELV circuits must be safely separated from the wiring of other circuits that are
not SELV, or the insulation of all conductors must be dimensioned for the higher voltage.
Protective extra-low voltage (PELV in accordance with IEC 61131-2 or IEC 61010-2-201)
Load current supplies with grounded 24 V DC output voltage require a safe connection to the
protective conductor and voltage limiting (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 S7-1500R/H redundant system is connected to the mounting
rail over a high-resistance RC combination in the R/H-CPU. This connection conducts high-
frequency interference currents and prevents electrostatic charges. Despite the grounded
mounting rail, the reference potential of the S7-1500R/H redundant system has to be
considered as ungrounded due to the high-resistance connection.
If you want to configure the S7-1500R/H redundant system with a grounded reference
potential, establish an electrical connection between the M connection of the CPU and the
protective conductor.
You can find a simplified representation of the potentials in the section Electrical
configuration (Page 173).
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 7-1 Components and required measures
Shut-off device for control system, sensors,
and actuators
Short-circuit and overload protection:
In groups for sensors and actuators
172
Reference to follow­ IEC 60364 (DIN VDE 0100) IEC 60204 (DIN VDE 0113)
ing figure
Main switch
①
Single-pole protection of
②
circuits
Disconnector
• With grounded second­
ary circuit: Single-pole
protection
• Otherwise: All-pole pro­
tection
S7-1500R/H redundant system
System Manual, 11/2022, A5E41814787-AD