A moulded case circuit breaker (MCCB) is a type of electrical protection device that is used to protect the electrical circuit from excessive current, which can then lead to overloading or a short circuit. In large-scale PV systems for system isolation and protection purposes these breakers are used instead of miniature circuit breakers (MCBs).
Operation of MCCB
Along with a temperature-sensitive device (the thermal element), the MCCB makes use of a current-sensitive electromagnetic device (the magnetic element) so that for protection and isolation purposes it can provide the trip mechanism. This enables the MCCB to provide:
Overload Protection
Electrical Fault Protection against short circuit currents, and
Electrical Switch for disconnection.
Overload Protection
With the help of a temperature-sensitive component, MCCB provides overload protection. This component is essentially a bimetallic contact: a contact that has two metals that when exposed to high temperatures expand at different rates. The bimetallic contact will allow the electric current to flow through the MCCB during the normal operating conditions. Whenever the current exceeds the trip value, the bimetallic contact gets heated and bends away due to the different thermal rates of heat expansion within the contact.
