Siemens Assembling an S7-400 with Process I/Os, Definition of a Grounded Supply TN-S Network

Wiring the S7-400

4.4Assembling 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

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

Automation System S7-400	Hardware and Installation	4-5
A5E00850741-01