Siemens SIRIUS 3RT Series System Manual page 172

SIRIUS 3RT2 contactors/contactor assemblies
2.7 Accessories
Surge suppressor Suitable for
Control
voltage
Varistor AC/DC
RC AC/DC
elements
The drop-out speed falls to zero once or twice for a few milliseconds:
1)
● Safe drop-out is always ensured during current-free switching.
● When switching with a current present, the contacts are subjected to a higher thermal
load. This can lead to an overload when switching at the high current limit.
172
Overvoltage Effect
is limited ...
OFF-delay
To varistor 
becomes only
voltage
slightly longer
(2 to 5 ms)
OFF-delay
According 
remains
to
unchanged
dimensionin
g Rates of rise of

voltage are
attenuated
Advantages/disadvantages
Energy absorption
Advantag 
es
Non-critical

dimensioning
Simple

implementation
Attenuation only
Disadvan 
above U
tages
VDR
RF attenuation
Advantag 
es
Well suited to AC

voltage
Attenuation

independent of
levels
High inrush current
Disadvan 
tages
Sensitive to

harmonics
System Manual, 01/2011, A8E56203870002-03
Preferred
application
Suitable for
most standard
applications,
e.g. in the
SIMATIC
environment
With critical
operating times
SIRIUS Innovations