The function principle of MCB and MCCB is very similar. However, there are many differences between them.
Abbreviation and definition
MCB stands for miniature circuit breaker. MCCB stands for molded case circuit breaker. Both devices protect installations against overcurrent and short circuits. They have also an isolation function. By using their handles, you can easily disconnect the load from the supply.
The operation and application of the MCCB are similar to that of the MCB, however, MCCB has the air-break mechanism contained within a molded case housing made from a very robust non-conducting material.
As the name suggests, MCB is smaller in size. 1 pole of MCB is around 17,5mm. The dimension of the MCCB is much bigger than MCCB.
You can see the dimensional comparison of 63A MCB and MCCB below. (3 pole – ABB brand)
MCBs are usually up to 125A. However, MCCBs are usually up to 3200A. MCCBs can carry more currents. The wide range of current ratings available from molded-case circuit breakers allows them to be used in a wide variety of applications.
Electrical and mechanical accessory options
Accessories increase the function of a circuit breaker. While the accessory options of MCBs are limited, a large number of accessories can be attached to MCCBs.
The physical size of three-pole and four-pole MCCBs allows these accessories to be internally mounted, although there are some restrictions concerning combinations of these that can be co-mounted. For example, either a shunt trip or an under-voltage release can be incorporated, but not both. Also, due to the much larger physical size of these devices compared with MCBs, additional safety features normally include interphase barriers and terminal shrouds to provide IP2X ingress protection at the terminals.
Molded case circuit breakers and miniature circuit breakers are rated for their maximum interruption capacity, or Icu (Interruption Capacity Ultimate) and Ics (Interruption Capacity Service) as part of their compliance with standards for suitability and safety. The breaking capacities of MCCBs are much higher than MCBs. (up to 200kA) It means that an MCCB can withstand and break high currents compare to MCCB.
MCCBs can communicate with each other by adding modules or by choosing electronic models. Digital trip units have built-in communication options to allow all protection, monitoring, and control information to be transmitted back to a central location. MCBs do not have this feature.
Adjustment of current and time delay
The tripping currents of MCCBs can be adjusted using dipswitches, potentiometers, or trip units. The long-delay tripping characteristics of an MCB are typically fixed, and the MCCB’s characteristics are adjustable. When using MCCB for distribution applications, the protective characteristics can be attained easily by using an electronic MCCB that has variable long delay tripping characteristics.
Location in the circuit
While MCCB is used as an upstream breaker, MCB is generally preferred in the branch circuits. MCCBs are used in upstream circuits of large commercial and industrial installations. MCBs are used for minor sub-circuit supply in commercial and domestic installations.
Number of poles
MCBs are produced with 1, 2, 3, 4, 1 + N, 3 + N poles. MCCBs are produced with 3 and 4 poles.
The electric arc interruption system used on MCCBs allows the short-circuit currents of very high value to be interrupted extremely rapidly. The considerable opening speed of the contacts, the dynamic blasting action carried out by the magnetic field and the structure of the arcing chamber contribute to extinguishing the arc in the shortest possible time, notably limiting the value of the specific let-through energy I2t and the current peak. MCCB has more big and efficient arching chambers compared to MCB.
MCB has a simple and safe structure that does not require maintenance or inspections. However, the MCCB is designed with many updated parts and must be sufficiently serviced and inspected. Thus, MCB is not suitable for applications intended for frequent short circuit interruption.
When MCCB trips from overload or short circuit, the handle will stop in the center between ON and OFF to indicate the tripping state. To remake, turn the handle to ON after resetting. Concretely, when the handle is turned over to the OFF position, the released cradle and hook will be engaged, and the mechanism will be restored to the OFF state to complete the reset. MCB does not have a trip indication in the center of the handle.
The trip button is a pushbutton for mechanically tripping the circuit breaker from the outside. A circuit breaker with a trip button can be easily tripped by pressing the trip button without electrical tripping by a voltage trip device or under-voltage tripping device or overcurrent tripping by application of current higher than the rated current to the circuit breaker. Therefore, it is easy to make sure that the circuit breaker has been reset and the external operation handle has been operated to reset, and, on circuit breakers with accessories, such as alarm switches, the control circuits can be checked easily. MCCB has a trip button on the device but MCB does not have any.