“Contactors”- The Switching agents

A homophone to contractors, contactors take contract for switching a load.

Ratings of contactors are mentioned in Ampere (A), and primarily are selected on the basis type of load which it is assigned to switch.

The load can be of various types. Most widely loads can be classified as AC & DC. Further they can be classified on the basis of application such as lighting load, motor load or capacitor banks.

Depending on the type of load/application, IEC947/ IS 13947 has defined certain utilization categories

AC1 - Non-inductive or slightly inductive loads, resistance furnaces

AC2 - Slip ring motors; starting, switching off

AC3 - Squirrel-cage motors; starting, switching off motors during running

AC4 - Squirrel-cage motors; starting, plugging, inching

AC5a - Switching of electric discharge lamp controls

AC5b - Switching of incandescent lamps

AC6a - Switching of transformers

AC6b - Switching of capacitor banks

AC7a - Slightly inductive loads in household appliances and similar applications

AC7b - Motor loads for household applications

AC8a - Hermetic refrigerant compressor motor control with manual resetting of overload releases

AC8b - Hermetic refrigerant compressor motor control with automatic resetting of overload releases

DC1 - Non-inductive or slightly inductive loads, resistance furnaces

DC3 - Shunt-motors: starting, plugging, inching, dynamic braking of d.c motors

DC5 - Series-motors: starting, plugging, inching, dynamic braking of d.c motors

DC6 - Switching of incandescent lamps

There is a common misconception among the masses that they need to use different contactors for different loads; i.e. different contactors are to be used for switching a lighting load (AC1) and induction motor (AC3).

A particular contactor also can be for AC1, AC3, AC4 and AC6b applications. A 9A, AC3 rated contactors can be used for say 4A in AC4 as well as 25A in AC1 application. There are certain de-ratings factors to be considered; which all manufacturers readily provide.

However, nearly all manufacturers have different ranges of contactors for different set of application depending on their product range and marketing strategy. For example Siemens has a different range of AC1 contactors. Nearly all the major players of switchgear market such as #Siemens, #ABB, #L&T, and #Schneider have Capacitor duty (AC6b) contactors, for switching of capacitor banks. Siemens also have special contactors for Hoisting application.

So choose your “switching agent” efficiently to provide or ask solution effectively.

It’s not a Rocket Science but contactors are even used to fire a rocket :)

So, Happy Selecting!