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 4I_n to 7I_n 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 5I_n to 10 I_n in the AC system whereas its value lies in the range of 7I_n to 15I_n 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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