text: what is the differance between mcb and mccb in theory of operation?   there are wide range of circuit breaker equipment, both mcb and mccb(molded case circuit breaker). the range of mcb boards are highly durable and allow the installer maximum flexibility. there is a huge number of variations with current ratings from 6 amps to 40 amps.  different series including high rupture capacity, single to four pole.  high breaking capacity: 20 - 15 - 10 - 6 k a nominal rated currents from 0.5 to 63 a wide range of the executions for both the mcbs and the accessories combined main contacts.   the traditional molded-case circuit breaker uses electromechanical (thermal magnetic) trip units that may be fixed or interchangeable. an mccb provides protection by combining a temperature sensitive device with a current sensitive electromagnetic device. both these devices act mechanically on the trip mechanism.  depending upon the application and required protection, an mccb will use one or a combination of different trip elements that protect against the following conditions:  thermal overloads; short circuits; and ground faults.