Siemens SIRIUS 3RT Series System Manual page 145

Switching off
During the switch-off of AC-operated contactors, the contactor may no longer switch off in
case of control circuit interruption due to an excessive line capacity of the control cable.
The following counter-measures can be taken:
● Changed circuit topology to allow for the application of shorter control cables.
● Application of DC-operated contactors.
● Reduced control voltage.
● Application of a contactor whose magnet coil has a higher holding power.
● Parallel connection of an ohmic resistance for increased holding power.
Sizing of the parallel resistance
For reasons of cost effectiveness, P
Table 2- 17 Calculation of the maximum cable length
For pushbutton switch control
For pushbutton switch control with a three-core cable, a line
capacity of 0.6 μF/km (2 x 0.3 μF/km) should be expected.
U Rated control supply voltage in V
S
S Holding power of the contactor in VA
H
SIRIUS Innovations
System Manual, 01/2011, A8E56203870002-03
SIRIUS 3RT2 contactors/contactor assemblies
Power of the additional resistance
should be lower than 10 W.
P
For maintained-contact operation
For maintained-contact operation with a two-core cable, a
line capacity of 0.3 μF/km should be expected.
U Rated control supply voltage in V
S
S Holding power of the contactor in VA
H
2.4 Configuration
145