Medium Voltage Application Guide

14043.A
14042.A
SCHEMATIC DIAGRAMS
5.3 Contactor Control (Typical)
Medium voltage contactors have two methods of control.
single command operated control (SCO) - this requires a permanent signal to close and maintain the
contactor in the closed position. Removal of the control signal will open the contactor.
double command operated control (DCO) - this requires two separate momentary contacts; one for the
close command and one for the open command. The DCO control method typically uses normally open,
spring return pushbuttons for both the open and close commands.
Typically, command signals require an external voltage source and the contactor controller itself requires a separate
auxiliary voltage source. Depending on the contactor make and model, electrical options are available. Some
examples are:
Undervoltage shunt trip
Lock-out solenoid
Racking solenoid
Auxiliary contacts
Racking contacts
Fuse blow indicator contacts
only used with DCO control
needs to be externally energised before contactor main poles can be electrically
operated
needs to be externally energised before a withdrawable contactor can be moved
between the test and service positions
indicate the electrical state of the main contactor poles
indicate whether a withdrawable contactor is in the service or test position
indicate fuse condition. - operated by striker pin and only available on contactors
with integral medium voltage fuses
The following examples show typical contactor control circuits:
Single command operated contactor control (typical)
Auxiliary supply
KA1
3
Contactor controller
Control signal (maintained)
1
4
2
A
B
External trip contact (eg from MPR)
Control supply
Control input
A
B
Double command operated contactor control (typical)
1
A B C
3
2
A
B
C
Auxiliary supply
Contactor controller
External trip contact (eg from MPR)
Control supply
Close input
Open input
Page 174 Medium Voltage Application Guide 710-12280-00A