Product Manual

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Magnetic Starters

• Magnetic starters are used with larger motors or where greater control

is desired. The main element of the starter is the contactor, which is a

set of contacts operated by an electromagnetic coil. Energizing the coil

causes the contacts A to close, allowing large currents to be initiated

and interrupted by a control signal. The control voltage need not

be the same as the motor supply voltage, and is often low voltage

allowing the start and stop controls to be located away from the

power circuit.

• Closing the starter button contacts energizes the contactor

coil. An auxiliary contact, B, on the contactor is wired to seal in

the coil circuit. The contactor de-energizes if the control circuit is

interrupted by operating the stop button or if power is lost.

• The overload contacts are arranged so an overload trip on any

phase will cause all phases to open.

• Contactors are rated for various operating voltages and are sized

according to motor HP and type of duty expected.

Three-Phase

Motor

Figure 4.2

Magnetic Starter

Overload

Heaters

Contacts Operated by

Contactor Coil

Overload

Contacts

Contactor

Coil