Wiring the S7-400
4-19
S7-400 and M7-400 Programmable Controllers, Installation Manual
C79000-G7076-C424-01
4.11 Protection Against Inductive Surge Voltages
Integrated Overvoltage Protection
The digital output modules on the S7-400 have an integrated overvoltage
protection facility. Surge voltages are produced when inductors such as relay coils
and contactors are switched off.
Additional Surge Suppression
Inductors should only have additional surge suppression devices in the following
cases:
S When SIMATIC output circuits can be switched off by additionally fitted contacts
such as relay contacts.
S When the inductors are not controlled by SIMATIC modules.
Note: Consult the supplier of the inductors for the ratings of surge suppression
devices.
Example
Shown in Figure 4-6 is an output circuit which necessitates additional surge
suppression devices.
Contact in output circuit
Inductor requires a suppressor
(see Figures 4-7 and 4-8)
D
Figure 4-6 Relay Contact for EMERGENCY OFF in the Output Circuit
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