Rated Characteristics of Electrical Contactors

Rated characteristics of Contactors

1. Types:

• Electromagnetic
• Electro-pneumatic
• Pneumatic

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2. Interrupting Medium:

• Air
• Oil
• SF6 gas
• Vacuum

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3. 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.

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4. 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.

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5. 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.

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