3-Phase AC CircuitsElectrical WiringMotorsProtection

Rated Characteristics of Electrical Contactors

Rated characteristics of Contactors

  1. Types:
  • Electromagnetic
  • Electro-pneumatic
  • Pneumatic

Related Post: Important Terms and Definitions related to Motor Control and Protection

  1. Interrupting Medium:
  • Air
  • Oil
  • SF6 gas
  • Vacuum

Electric Magnetic Contactor  Thermal Overload relay  Rated characteristics of Electrical Contactors

Related Post: Abnormal Operating Condition and Causes of Induction Motors

  1. Rated values of voltages:
  • Rated voltage (Operational voltage)
    For a three phase contactors, the voltage between phases is called rated voltage or operational voltage.
  • Rated Insulation Voltage The voltage, on which performs the dielectric test.

Related Post: The Star-Delta (Y-Δ) 3-phase Motor Starting Method by Automatic star-delta starter with Timer.

  1. Rated Values of Current:
  • Rated Thermal Current: The maximum current, on which a Contactor operates continuously for eight (8) hours without increasing the temperature (increased with a permissible limit).
  • Rated Operational Current: A Manufacturer tells the rated operational current considering Contactor’s rated frequency, operational voltages, rated duty and utilization factor.

Related Post: Main Difference between Contactor and Starter.

  1. Rated duty and Serves Conditions:
  • Eight Hours Duty: A Contactor can carry the normal current for more than 8 hours. The contactor’s rated thermal current can be found by 8 hours duty.
  • Uninterrupted duty: A Contactor can be close for a long time (from 8 hours to many years) without interruption. However, Due to Oxidation and dust on contacts, Temperature may be increased.
  • Contactor’s making Capacity: Contactor’s rated making capacity is the value of current, on which the contacts of contactor can make the connections (i.e. Contactor can close their contacts) without arcing or melting. A.C contactor’s making capacity is defined according to the Current Symmetrical Component’s R.M.S value.
  • Contactor’s Breaking Capacity: Contactor’s rated breaking capacity is the value of current, on which the contacts of contactor can break the connections (i.e. Contactor can open their contacts) without arcing or melting. A.C contactor’s breaking capacity is defined according to the Current R.M.S value.

Related Posts:

Electrical Technology

All about Electrical and Electronic Engineering & Technology. Join us on WhatsApp at Electrical Technology Official Channel, to receive the latest content, articles, and updates. You can also like and follow our social media networks below, or subscribe with your email to receive premium engineering articles in your mailbox.


  1. Dear Waseem,
    thanks for the effort you are doing to spread the electrical knowledge. can you please explain that how could I install timers and the contact switch to AC motor(from start to end wiring how to wire) that will start and stop it on timing based phenomena as I am a newbie to electrical systems.


  2. Thanks for all this detailed information. It’s good to have found a blog where theres some expert advice about electrical information. Thanks again!

  3. Nice blog. Tnx for alway educating me. Pls can some 1 tell me the diffrence between current, voltage in details pls. And lastly the diff of. Ampere,watts, killowatt.

  4. please, have me. How to install magnetic contactor and overload, switch.For three phase motor. Please, send to me drowing.
    Thanks, you

Leave a Reply

Your email address will not be published. Required fields are marked *

Back to top button