WAGO-I/O-SYSTEM 750 XTR
Connect Devices 43
750-517/040-000 2DO 230V AC 1.0A/ Relay 2CO /XTR
Manual
Version 1.3.0
Pos: 70 /Serie 750 ( WAGO-I/O-SYST EM)/Anschli eßen/Anschl ussbeispi ele/Digitalausgänge/Kontaktschutzbeschaltung für R elaiskl emmen @ 12\mod_1339677705690_21.docx @ 97510 @ 2 @ 1
6.3
Protective Circuits for Contacts of Relay Modules
Switching off inductive loads such as contactors and solenoid valves can
generate transients with voltage peaks of up to several thousand volts. Very
often, these transients exceed the permissible limits specified in the EMC
standards. They must therefore be limited by using external protective circuits.
Furthermore, they cause an arc, which may destroy the switching contact, and
has a significant impact on the lifetime and safety of the relay. The following
protective circuits, which are directly connected to the source of the interference
in parallel with the consumer, have proved successful in practice:
Table 21: Protective Circuits for Contacts of Relay Modules
Protective Circuits
Additional
Off-Delay
Defined
Induction
Voltage
Limitation
Bipolar
Effective
Attenuation
Advantages and
Disadvantages
Figure 15: Diode
long
yes (U
D
)
no
Advantages:
• easy implementation
• cost-effective and
reliable
• uncritical dimensioning
• low induction voltages
Disadvantages:
• attenuation only via
load resistor
• long off-delay
Figure 16: Zener Diode
and Diode
medium to
short
yes (U
ZD
)
no
Advantages:
• uncritical dimensioning
Disadvantages:
• attenuation only above
U
ZD
Figure 17: Suppressor
Diode
medium to
short
yes (U
ZD
)
yes
Advantages:
• cost-effective
• uncritical dimensioning
• limitation of positive
and negative peaks
• suitable for AC voltage
Disadvantages:
• attenuation only above
U
ZD
Figure 18: Varistor
medium to
short
yes (U
VDR
)
yes
Advantages:
• high power absorption
• uncritical dimensioning
• suitable for AC voltage
Disadvantages:
• attenuation only above
U
VDR
