Siemens S7-400 installation manual Inductive Surge Voltage, Integrated Surge Arrester

Assembling and Installing Systems

A.10 How to Protect Digital Output Modules against Inductive Surge

Inductive Surge Voltage

Overvoltage occurs when inductive devices are switched off. Examples are relay coils and contactors

Integrated Surge Arrester

S7-400 digital output modules are equipped with an integrated surge arrester

Additional Overvoltage Protection

Inductive devices require additional surge arresters only in following cases:

•If SIMATIC output circuits can be switched off by additionally installed contacts (e.g. relay contacts).

•If the inductive loads are not controlled by SIMATIC modules.

Note: Consult the supplier of the inductors for the ratings of surge suppression devices.

Example

Figure A-8 shows an output circuit that requires additional surge arresters.

Contact in output circuit

Inductivitys requires a circuiting (see Figures A-9 and A-10)

D

Figure A-8 Relay Contact for EMERGENCY OFF in the Output Circuit

A-30	Automation System S7-400	Hardware and Installation
		A5E00850741-01