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Three-Phase Starter Diagrams |
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Three-phase combination magnetic
starters have two distinct circuits: a power circuit and a control
circuit.
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 three-phase motor.
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. Hands-Off-Auto switches, start timers, level controls
and other control devices may also be in series in the control
circuit. |
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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. |
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Low Voltage Transformer Control
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. |
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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. |
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