Special Measures For Interference-Free Operation - Siemens S5-135U/155U System Manual

3.3.4

Special Measures for Interference-Free Operation

Fitting Quenching
As a rule, inductances such as contactor or relay coils controlled by
Elements to SIMATIC S5 do not require external quenching elements in the circuit,
Inductances
because the quenching elements are already integrated in the modules.
Inductances should only be fitted with quenching elements
You can place freewheel diodes, varistors or RC networks in circuit with
inductances.
Circuitry for DC-Operated
Inductances
With Diode With Zener Diode
Figure 3-6 Quenching Circuits for Inductances
System Manual
C79000-G8576-C199-06
when SIMATIC S5 output currents can be switched off by additionally
fitted contacts, such as relay contacts. In this case the integrated
quenching elements in the modules are no longer effective;
if they are not controlled by SIMATIC S5 modules.
Installation Guidelines
Circuitry for AC-Operated
Inductances
With Varistor With RC Network
3-17