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(7 442)Contactor – what is a contactor and what is it used for?
A contactor is a type of electric switch. Its design and method of operation are similar to those of an electromagnetic relay. Unlike relays, contactors are used for switching main circuits, while relays – for switching auxiliary circuits. Contactors tolerate electrical surges and overvoltage well. They are characterized by high mechanical durability and allow to achieve a high switching frequency at very high operational reliability.
Contactor – differences between contactors and relays
Contactors differ from the relays not only in terms of their intended use, but also in their construction, as in general they are designed to conduct very high currents. In simple terms, it can be said that although their principle of operation is the same (transmitting an electrical signal after contacts are short-circuited) as that of electromagnetic relays, you can easily distinguish a contactor from a relay at first glance, because usually contactors have a large casing and a distinctive shape.
Contactors are capable of switching highly inductive or capacitive loads. They can be used, for example, to start a powerful electric motor. Relays are used to transmit control signals, including those that switch on the contactor. Relay contacts have a rather small current load capacity (typically up to 10 A) and coil voltage within the range of 5 to 24V. Moreover, a relay has a significantly smaller electromagnet than a contactor, and its contacts do not have any additional devices for electric arc extinguishing.
What is important, the contactor’s contact switching time is longer than in the case of a relay. Contactors (except for the quiet ones) work much louder than the relays.
Contactors – control and power supply methods
A contactor is switched on and powered in the same way as an electromagnetic relay. Its electromagnet is powered with a higher voltage than in the case of a relay. The coil rated voltage in certain versions of a contactor can reach up to 500V DC. Typically used values are: 12V DC/AC, 24V DC/AC, 48V DC, 110V AC, 230V AC.
Contactors – basic parameters
The basic parameters of a contactor include: contact configuration, maximum load current, coil control voltage and insulation voltage. In some applications, additional accessories, such as auxiliary contacts enabling to signal the operation of the contactor or to switch on the auxiliary circuit, will also be very important.
Choosing a right contactor for your application
The choice of a contactor depends on its function, the value of the switched current and voltage, type of voltage (AC/DC) and type of load. In order to choose a right contactor, one should know the circuit parameters mentioned before and choose a contactor with a rated current that is not lower than the one stated there. If used intensively in industrial applications, a contactor with the operating capability of the current specifications should be chosen, in which contacts can handle twice (or more) the load. It prolongs the service life of frequently switched contactors.
A contactor will prove useful in switching electric motors, heaters, pumps, sirens, fluorescent lamps, fans and other high-power electrical equipment
Accessories for contactors
Manufacturers offer many accessories for contactors, for example: auxiliary contacts, mechanical lock-out latches to maintain the contactor status, electronic timer modules to switch the contactor off or on after a certain time and overvoltage protectors.
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