Application – Three-Phase Motors
Three-Phase Starter Diagrams
The power circuit consists of a circuit breaker or fused line switch, contacts, and overload heaters connecting incoming power lines L1, L2, L3 and the
The control circuit consists of the magnetic coil, overload contacts and a control device such as a pressure switch. When the control device contacts are closed, current
flows through the magnetic contactor coil, the contacts close, and power is applied to the motor.
L1 L2 L3
Line Voltage Control
This is the most common type of control encountered. Since the coil is connected directly across the power lines L1 and L2, the coil must match the line voltage.
FUSES
CONTACTS
PRESSURE SWITCH OR
OTHER CONTROL DEVICE
O.L. CONTACTS
COIL
OVERLOAD
HEATERS AND/OR
SUBTROL PLUS
Low Voltage Transformer Control
MOTOR
FIG. 7
L1 L2 L3
This control is used when it is desirable to operate push buttons or other control devices at some voltage lower than the motor voltage. The transformer primary must match the line voltage and the coil voltage must match the secondary voltage of the transformer.
FUSES
CONTACTS
TRANSFORMER
OVERLOAD HEATERS AND/OR SUBTROL PLUS
FUSE
PRESSURE SWITCH OR OTHER CONTROL DEVICE
O.L. CONTACTS
COIL
MOTOR | FIG. 8 |
|
L1 L2 L3
External Voltage Controls
Control of a power circuit by a lower circuit voltage can also be obtained by connecting to a separate control voltage source. The coil rating must match the control voltage source, such as 115 or 24 volts.
FUSES
CONTACTS
PRESSURE SWITCH OR
OTHER CONTROL DEVICE
| O.L. CONTACTS |
COIL | TO SEPARATE |
| CONTROL VOLTAGE |
| SOURCE |
OVERLOAD
HEATER AND/OR
SUBTROL DEVICE
MOTOR
FIG. 9
32
