Using Long Control Cables - Siemens SIRIUS 3RT Series System Manual

Control circuit
The diagram below shows the control circuit for the main circuit depicted above.
Figure 2-17
2.4.11

Using long control cables

Malfunctions caused by long control cables
If long control cables are required for the control circuits of contactors or relays, malfunctions
may occur during switching under certain conditions. As a result of these malfunctions, the
contactors may no longer be able to switch on or off.
Switching on
Due to the voltage drop in long control cables, the control voltage applied to the contactor
may fall below the threshold value at which the contactor switches on. This affects both DC-
and AC-operated contactors.
The following counter-measures can be taken:
● Changed circuit topology to allow for the application of shorter control cables.
● Increased conductor cross-section.
● Increased control voltage.
● Use of a contactor whose magnet coil has a lower closing power.
Calculation of the maximum cable length:
The maximum permissible simple cable length l
equations given below.
SIRIUS Innovations
System Manual, 01/2011, A8E56203870002-03
Control circuit of the contactor assembly for star-delta (wye-delta) start
SIRIUS 3RT2 contactors/contactor assemblies
can be roughly calculated using the
zul
2.4 Configuration
141