MCCB is actually the need to understand MCB is clear to most of the users.   MCB is for low current interruptions and has fixed current rating for trip. It will not trip at earth fault. It has low KA rating, it is suitable for simple over current application, less than 100 A and has low cost. MCCB (Molded case C.B) is for high current application normally above 100 A and also programmable/adjustable for earth fault , over/under voltage protections etc. It has high KA ratings, hence costly.