How to Choose a contactor for a motor
A contactor is a type of electrical switch which is used for the switching of an electrical circuit. The contactors are used for the switching purpose in electrical power circuits. The contactors are commonly used with the big motors which are used in huge industries for several purposes. The contactor is used with the motors to protect the motors from different overload conditions. A contactor protects a motor from the overcurrent in the motor. The power of the contactor is always greater than the power of the circuit to which it is connected. The relays and typical switches are connected indirectly with the circuit but the contactors are attached directly with the circuit. The switching devices handling current rating more than 15 amps are called contactors. Contactors are usually used with the motors as a switching device. The contactors can easily suppress and control the arc produced in heavy motors. The contactor is used in the motor to control the flow of current. In short, the motor flow is controlled with the help of the contactor. The contactor is also termed as a relay. The relays and the different contactors perform the basic operation which is called the switching.
Choosing the right contactor for a motor is an important task. Different parameters of a motor are first analyzed to choose the right contactor. The load type of the motor is considered while choosing a contactor for the motor. The duty cycle of the motor is considered while choosing a contactor. The amount of current drawn for the motor is also considered to choose a contactor. The main important parameters while choosing a contactor are:
Contact (switch) Ratings:
The contact ratings are divided into two types. One is the maximum switching voltage and the second is the maximum switching current.
The maximum switching voltage that a switch can bear is selected on the ratings of the circuit or the motor on which the contactor will be used. Similarly, the maximum current rating that a contactor will bear is also selected as per the rating of the motor. The maximum inrush current during the startup of a motor is also considered while selecting a contactor.
The coil ratings considered while choosing a contactor are:
- Pick-Up Voltage: The voltage at which all the switches will be in their operating position is called the pick-up voltage. The pick-up voltage of a motor is considered while choosing a contactor.
- Rated Coil Voltage: The contactor coil voltage should be equal to the voltage of the circuit powering the coil while choosing a contactor.
- Drop-Out Voltage: The drop-out voltage of the contactor is the voltage at which all the switches of the contactor will be in an un-operated position.
- Operating Current: The current of the coil at the rated coil voltage is considered before choosing a contactor.
The auxiliary contacts are used in between the contactors and the circuits for different functionalities. The auxiliary contacts must be considered while choosing a contactor.
The three parameters considered while selecting a contactor are discussed above. The selection of the right contactor for the motor is a more important parameter than choosing the right contactor for the motor.
Whereas the two steps while selecting the right contactor for a specified motor are:
- Gathering correct information about the motor.
- Extracting the right information from the right datasheet of the product.
The electrical properties of a motor should be studied in detail in order to choose the right contactor for the motor. The motor comes in with proper datasheet which can be considered while selecting the right contactor for the motor. The common and basic electrical properties are also mentioned on the motors sometimes with proper tags. The parameters like the power of the motor which is usually in hose power, motor voltage, and current should be considered from the tag of the motor or from the datasheet provided with the motor. A right datasheet must be considered while determining the properties of the motor.
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