Rated Characteristics of Electrical Contactors

Types

• Electromagnetic
• Electro-pneumatic
• Pneumatic

Interrupting Medium

• Air
• Oil
• SF6 gas
• Vacuum

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.

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.

Rated Duty and Service Conditions

• 8-Hour Duty：The contactor can carry normal current for over 8 hours. Its rated thermal current is determined based on this duty cycle.
• Continuous Duty：The contactor can remain closed indefinitely (from 8 hours to several years) without interruption. However, oxidation and dust accumulation on contacts may increase temperature.

Contactor Making and Breaking Capacity

• Rated Making Capacity：The maximum current at which the contactor can close its contacts without arcing or melting. For AC contactors, this is defined by the RMS value of the symmetrical current component.
• Rated Breaking Capacity：The maximum current at which the contactor can open its contacts without arcing or melting. For AC contactors, this is defined by the RMS current value.