The contactor is an electrically controlled switch used for switching an electrical power circuit, similar to a relay except with higher current ratings and a few other differences, the contactor is controlled by a circuit which has a much lower power level than the switched circuit.
Contactors come in many forms with varying capacities and features. Unlike a circuit breaker, a contactor is not intended to interrupt a short circuit current. Contactors range from those having a breaking current of several amperes to thousands of amperes and 24 V DC to many kilovolts. The physical size of contactors ranges from a device small enough to pick up with one hand, to large devices approximately a meter on a side.Contactors are used to control electric motors, lighting, heating, capacitor banks, thermal evaporators, and other electrical loads.
Contactors are rated by designed load current per contact (pole),maximum fault withstand current, duty cycle, design life expectancy, voltage, and coil voltage. A general purpose motor control contactor may be suitable for heavy starting duty on large motors; so-called “definite purpose” contactors are carefully adapted to such applications as air-conditioning compressor motor starting.
IEC utilization categories
The current rating of the contactor depends on utilization category. Example IEC categories in standard 60947 are described as:
- AC-1– Non-inductive or slightly inductive loads, resistance furnaces
- AC-2– Starting of slip-ring motors: starting, switching-off
- AC-3– Starting of squirrel-cage motors and switching-off only after the motor is up to speed. (Make Locked Rotor Amps (LRA), Break Full Load Amps (FLA))
- AC-4– Starting of squirrel-cage motors with inching and plugging duty. Rapid Start/Stop. (Make and Break LRA)
Relays and auxiliary contact blocks are rated according to IEC 60947-5-1.
- AC-15– Control of electromagnetic loads (>72 VA)
- DC-13– Control of electromagnets
3-phase motors 50/
|Rated heat current (A)||20||20||32||40||50||60||80||80||125||125|
|Electrical life||AC3 (x10⁴)||100||100||100||100||80||80||60||60||60||60|
|Mechanical life (x104)||1000||1000||1000||1000||1000||800||800||800||800||600||600|
|Number of the contacts||3P+NO||3P+NC+NO|
|Rated working current (A)||AC3||115||150||170||205||245||300||410||475||620|
3-phase motors 50/
60Hz in category
|Rated heat current (A)||200||250||250||275||315||400||500||700||1000|
|Electrical life||AC3 (x10⁴)||200||60||60||50||50||50||30||30||20|
|Number of the contacts||300||300||300||300||300||300||100||100||100|