Wiring the S7-400
4-5
AutomationSystem S7-400 Hardwareand Installation
A5E00850741-01
4.4 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

Variouscomponents 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.
Table4-1 VDE Specifications for Assembling a Programmable Controller
Compare... Ref. to
Figure
4-1,
page
4-6
VDE 0100 VDE 0113
Disconnection element for control
system, sensors, and actuators
¡... Part 460:
Main switches
... Part 1:
Isolating switches
Short-circuit and overload protection:
in groups for sensors and actuators
©... Part 725:
Single-pole
protection of
circuits
... Part 1:
•With
grounded
secondary
circuit:
single-pole
protection
•Otherwise:
all-pole
protection
Load current PS for AC power circuits
with more than five items of
electromagnetic apparatus
¢Isolation by
transformer is
recommended
Isolation by
transformer is
required

Rule: Grounding the Load Current Circuits

Load current circuits must 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 (TerminalL- 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.