Wiring the S7-400
4-5
S7-400 and M7-400 Programmable Controllers Hardware and Installation
A5E00069481-04
Determining the Load Current
The required load current is governed by the total current of all sensors and
actuators connected to the outputs.
During a short-circuit, a current of two to three times the rated output current flows
briefly at DC outputs before the switched electronic short-circuit protection
becomes effective. When selecting the load current power supply, therefore, you
must ensure that the increased short-circuit current is available. With unregulated
load current power supplies, this excess current is generally ensured. With
regulated load current power supplies, particularly at low output levels (up to 20 A),
you must ensure a suitable excess current.
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
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.