About a Typical Contactor Control
KVAL 990-F4 Service Manual
4-10
About a Typical Contactor Control
Unlike general-purpose relays, contactors are designed to be directly connected to high-current
load devices. Contactors are designed to control and suppress the arc produced when interrupting
heavy motor currents.The figures below shows a block diagram of a typical contactor circuit with
typical voltages.Thermal overload relays are commonly attached to the contactor. They offer pro
-
tection for motors in the event of overload or phase failure. A Reset button is included to clear an
error in the relay.
FIGURE 4- 1.
Block Diagram of a Common Contactor Circuit
High Voltage may cause personnel
injury or death.
Troubleshooting checks
must
be performed by a Qualified Electrical Technician
.
PLC
Output
Fuse(s)
Line
Voltage
(Power)
Contactor
Control
(Coil)
Input
Power
Input
Power
Output
Control Circuit
Common
ON
Should measure
Control Voltage
120 VAC here
Should measure
Line Voltage here
Should measure
Line Voltage here
Line Voltage here
Should measure
Relay
120 VAC
DC -
Should measure
24 VDC here
Control Voltage
Motor
ON
Thermal
OverLoad
RESET
#2
#2
Pre 2006 Machines do not have this Relay.
Measure 120 VAC at the Control Coil
Schematic Drawing of Contactor and Thermal Overload
Note:
Pre-2006
machines may
not contain the
24 Volt relay.
120 Vac is
directly fed into
the Control Coil.
Check the input
circuitry to the
Control Coil for
120 Vac.
