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What is the instantaneous tripping current of ‘B’ characteristic MCB with In as rated current?

What is the instantaneous tripping current of ‘B’ characteristic MCB with In as rated current? Correct Answer 3 - 5 In

Miniature Circuit Breaker:

  • Miniature Circuit Breaker is used to protect the circuits from short circuit faults.
  • It is used in the place of Fuse when the amount of electricity is increasing in the wire.
  • The MCB turns off and the result is it breaks the circuits. It prevents from burning of home appliances.
  • MCB can protect the instrument from overloading but not against leakage.
  • In the case of MCB, the faulty zone of an electrical circuit can be easily identified.
  • It is very simple to resume the supply by using MCB.
  • MCB is safer to handle. 

 

Type B MCB Characteristics:

  • A current equal to 3 In is passed through all poles starting from cold.
  • The opening time shall be not less than 0.1 s and not more than: - 45 s for rated currents up to and including 32 A,- 90 s for rated currents above 32 A.
  • A current equal to 5 In is then passed through all poles, again starting from cold. The circuit-breaker shall trip in a time less than 0.1 s. 
  • Above 3 In up to and including 5 In.

Important Points

Standard ranges of instantaneous tripping:

Type B MCB: Above 3 In up to and including 5 In.
Type C MCB: Above 5 In up to and including 10 In.
Type D MCB: Above 10 In up to and including 2 ln.

Additional Information

Type C MCB Characteristics:

  • A current equal to 5 In is passed through all poles starting from cold.
  • The opening time shall be not less than 0.1 s and not more than:- 15 s for rated currents up to and including 32 A,

     - 30 s for rated currents above 32 A.
  • A current equal to 10 In is then passed through all poles, again starting from cold.
  • The circuit-breaker shall trip in a time less than 0.1 s.

Type D MCB Characteristics:

  • A current equal to 10 In is passed through all poles starting from cold.
  • The opening time shall be not less than 0.1 s and not more than:- 4 s for rated currents above 10A up to and including 32 A, - 8 s for rated currents up to an including 10 A and above 32 A.
  • A current equal to 20 In is then passed through all poles, again starting from cold.
  • The circuit-breaker shall trip in a time less than 0.1 s.

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