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Types of MCB And Its Marking

There are three types of MCBs.

Type B MCB

  • They are suitable for resistive load like oven, heater, GLS lamp etc. 
  • The trip system operates between 3In to 5In in the AC system whereas its value lies in the range of 4In to 7In in the DC system ( Where In is equal to rated current of MCBs )

Type C MCB

  • They are suitable for where high inrush current flow at the time of switching i.e. switching of inducting load such as motors, air conditioner, fluorescent lamp, transformers etc. 
  • The magnetic trip system operates between 5In to 10 In in the AC system whereas its value lies in the range of 7In to 15In for DC system ( Where In is rated current of MCB )

Type D MCB

  • They are suitable for protection of electrical circuits in which very high inrush current flows. 
  • Its typical value is 12 – 15 times the thermal rated current. 
  • The characteristic of type B, type C and type D MCBs have same overload tripping characteristic.

Marking and Symbol of MCB

  • The rated short circuit capacity for AC and DC in ampere is expressed in one rectangle if it is valid for both AC and DC.
  • If the rated short circuit capacity is different for AC and DC it shall be indicated by two adjacent rectangles with symbol for AC and DC.
  • The time constant is expressed as T15 Milli second and if it is associated with rated short circuit current capacity.


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