IEC Standard & Utilization Category
IEC is an international organization which publishes and prints the standard for each and every electrical or electronic device. The standard for any product is a set of rules and regulations which also carries the product characteristic details. Contactors follow the IEC – 60947-4 standard.
What are Contactors?
Contactors are an electromechanical device which performs switching in an electrical system. It is used for enhanced switching particularly in case of Motor Loads as a frequent switching may be required for these kinds of load. These needs to be mentioned here that contactor is only a switching device and cannot protect the circuit against any kind of fault.
As the word electromechanical suggests, the contactor is equipped with a Coil & a set of contacts (one fixed & one moving contact). The electrical supply is given to the coil through which a magnetic field is generated and the moving contact is attracted towards the fixed contact resulting in closing of contactor. Once the supply is disconnected the magnetic field is lost and contactor opens.
Accessories of Contactors
Certain accessories can be used with contactors with respect to the application it is being used such as:
- Mechanical Interlock: For interlocking 2 contactors in order to use for Power Transfer application.
- Dust Cover: It can be used for application in dusty or moist environmental condition.
- Surge Suppressor: Protects the coil against voltage surges which can damage the coil.
- Latch blocks: For starter applications.
- Relay: this device gets connected with contactor and trips in case of fault by disconnecting the supply being fed to contactors thus, protecting the circuit
Contactors are majorly used for applications where frequent or high switching is required. For ex Hoisting, Power Transfer, Motor Applications, Capacitor Switching etc. Contactors are also widely used for control & signaling purpose and for circuits associated with PLC.
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 & switching off of slip ring motor.
- AC-3 – Starting of Squirrel Cage motors and switching-off only after the motor is up to speed.
- AC-4 – Starting of squirrel-cage motors with inching and plugging duty.