Main Difference between Contactor and Starter

Difference between Contactor and Motor Starter

The magnetic starter is very similar to the magnetic contactor in design and operation. Both have the feature of operating contacts when the coil is energized. The main difference between contactors and starters is the use of overload heater element (a sensitive coil which monitors the generated heat by excessive current and changes in ambient temperature) in the starter to protect the motor from overheating and provide load protection).

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A Motor Starter is a basically a contactor with the addition of an overload relay which will drop out the coil voltage in case of motor overload condition.

A Contactor is an electrically control switch same as a relay. It is used for switching the current to ON and OFF a circuit. Contactor won’t provide protection against overload protection. It is used to control the heating circuits, electric motor and automated industrial equipment.

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A Motor Starter is a combined device of contactor and over load relay. In motor starter, contactor controls the flow of electric current to the connected motor and repeatedly make and break (interrupt) the power circuit from main power supply. The overload protection block in a starter protects the motor from drawing excessive current and overheating and burning out the circuit.

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A Contactor is a separate part of a motor starter which can be used as a power control device as well. It is used where frequent opening and closing (ON – OFF) operation needed in electrical equipment such as motors, light and heaters etc. According to NEMA, The main function of the contactor is to repeatedly establish and interrupt and electrical power circuit i.e. to make and break the load circuit from power supply.

A Contactor depends on information from the motor starter control system and energizes and de-energizes the motor circuit.

A Motor starter gets information from contactor and systems of contactors to energize and de-energize the motor.

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A Contactor function is same as a circuit breaker or switch but the working principle is different. For instance, if a switch or circuit breaker is at ON position and a control system sends an “open operation signal”, it will not open the circuit until someone open the switch manually or it will melt or burn. This is not the case with the contactor i.e. if something happens wrongs to the power supply connected to the contactor circuit, the contactor circuit will immediately open the closed contacts held by energized coil. This way, contactor protects the motor and operation process of the motor circuit.

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Motor Starter can be a single circuit breaker or contactor or a system of motor starters, autotransformer to reduce the voltage for motor starting operation or a solid state device like VFD (variable frequency drive) which control the waveform sent to the motor to control motor starting operation. Starter is rated in amperes or related to motor HP (Horse Power rating) and protect the motor circuit from overload surges and prevent overheating.

A contactor is one of the modified versions of relay and a part of Motor Starter. It is rated in voltage (or by designed load current per contact (pole) and applies the voltage to the contactor coils to make or interrupt the power circuit.

In short, if you have a starter, then you are having a Contactor and Overload protection in a single unit. If you have a contactor, you are not having the overload protection unit.

The term “Motor Starter” referred to an enclosed assembly box which includes “contactor, control or autotransformer (if any), fuses and overload relay”?

i.e.

Starter = Contactor + Overload Relay

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Related Posts:

• What is Motor Starter? Types of Motor Starters and Motor Starting Methods
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• Direct Online Starter – DOL Starter Wiring Diagram for Motors
• What is a Contactor ? Types, Working and Applications