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The thermal protection against overload is designed with a time delay to allow short duration overcurrent, which is a normal part of operation for many devices. However, as soon as the current exceeds the adjusted trip value, the contact will start to heat and expand until the circuit is interrupted. Under normal operating conditions, the contact allows electric current through the MCCB. MCCBs have a bimetallic contact what expands and contracts in response to changes in temperature.

Overload protection is accomplished by means of a thermal mechanism.

Molded Case Circuit Breaker Operating MechanismĪt its core, the protection mechanism employed by MCCBs is based on the same physical principles used by all types of thermal-magnetic circuit breakers. This allows them to be used in both low-power and high-power applications. MCCBs are available with current ratings that range from low values such as 15 amperes, to industrial ratings such as 2,500 amperes.

The wide range of current ratings available from molded-case circuit breakers allows them to be used in a wide variety of applications.

Switching a circuit on and off – This is a less common function of circuit breakers, but they can be used for that purpose if there isn’t an adequate manual switch.

Protection against electrical faults – During a fault such as a short circuit or line fault, there are extremely high currents that must be interrupted immediately.

Protection against overload – currents above the rated value that last longer than what is normal for the application.As with most types of circuit breakers, an MCCB has three main functions: An additional difference is that MCCBs tend to be much larger than MCBs.

The main distinctions between molded-case and miniature circuit breaker are that the MCCB can have current ratings of up to 2,500 amperes, and its trip settings are normally adjustable. Molded Case Circuit Breaker Definition and FunctionĪ molded case circuit breaker, abbreviated MCCB, is a type of electrical protection device that can be used for a wide range of voltages, and frequencies of both 50 Hz and 60 Hz. They are also used in applications of any current rating that require adjustable trip settings, which are not available in plug-in circuit breakers and MCBs. Molded case circuit breakers are a type of electrical protection device that is commonly used when load currents exceed the capabilities of miniature circuit breakers.