Assembling An S7-400 With Process I/Os - Siemens SIMATIC S7-400 Hardware And Installation Manual

Wiring the S7-400
4.5

Assembling an S7-400 with Process I/Os

Definition of a Grounded Supply (TN-S Network)
In grounded supplies, the neutral conductor of the system is grounded. A single
fault between a live conductor and ground or a grounded part of the installation
results in tripping of the protective devices.
Components and Protective Measures
Various components and protective measures are specified for assembling a full
installation. The types of components and whether the protective measures are
mandatory or recommended depends on the VDE specification applying to your
installation, VDE 0100 or VDE 0113. The following table relates to Figure 4-1.
Table 4-1 VDE Specifications for Assembling a Programmable Controller
Disconnection element for control
system, sensors, and actuators
Short-circuit and overload protection:
in groups for sensors and actuators
Load current PS for AC power circuits
with more than five items of
electromagnetic apparatus
Rule: Grounding the Load Current Circuits
Load current circuits should be grounded.
Reliable functional safety is provided by the common reference potential (ground).
Provide a detachable connection to the protective ground conductor at the load
current power supply (Terminal L- or M) or on the isolating transformer (Figure 4-1,
). In the event of faults in the power distribution, this will facilitate the locating of
ground faults.
4-8
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S7-400 and M7-400 Programmable Controllers, Installation Manual
Ref. to VDE 0100
Figure
4-1
... Part 460:
Main switches
... Part 725:
Single-pole
protection of
circuits
Isolation by
transformer is
recommended
C79000-G7076-C424-01
VDE 0113
... Part 1:
Isolating switches
... Part 1:
With
grounded
secondary
circuit:
single-pole
protection
Otherwise:
all-pole
protection
Isolation by
transformer is
required