Introduction

Moulded Case Circuit Breaker is also commonly referred to as MCCB. MCCB is an automatic electrical safety device used to protect the electrical equipment from overload, short circuits, earth faults and instant overcurrent. 

MCCB is an advancement of previously used MCB(Miniature Circuit Breaker), and MCCB is a specific type of circuit breaker. The term moulded case refers to the construction of the circuit breaker, which is an assembled unit in a supportive housing of insulating material.

MCCB is available from 32 Amps to 1600 Amps with a voltage range of 230V to 1.1kV. 

Features of MCCB

Following are some of the features of MCCBs-

• The tripping circuit is moveable of Moulded Case Circuit Breaker.
• It has single, two, three, or four-pole versions.
• They are suitable for use in heavy-duty industrial applications.
• It has a high breaking capacity.
• They are primarily used in heavy current circuits.
• MCCB’s rating current varies from 10 to 200 Amps- that is the maximum rating current circuit should draw.

Working Principle of MCCB

MCCBs are specially designed to perform both the function of disconnecting and protecting the electric power current. It is commonly used as an electrical safety device when the electric current load is significantly higher than the limit of a miniature circuit breaker.

MCCBs can instantly detect the difference between an overcurrent and a short circuit. Therefore, they use a temperature-sensitive device ( the thermal element) with a current sensitive electromagnetic device( the magnetic element) to provide the tripping mechanism for protecting purposes. 

Therefore, to protect the electrical equipment from severe damage, MCCB allows minimal overcurrent for a brief time, and as the current level starts rising, it opens up. That enables it to provide overload protection and electrical fault protection against short circuit current. 

Along with protection against short circuits, MCCB can also be used for switching circuits. MCCB is often used for industrial purposes, but it can be utilised for higher current ratings and fault levels if used for a few domestic purposes.

• Overload protection 

MCCB provides overload protection through the temperature-sensitive component. This component is nearly a bimetallic contact- a contact which consists of two metals that extend at different rates when exposed to elevated temperatures. 

During the normal operating conditions, the bimetallic contact lets the electric current flow through the MCCB. However, when the electric current exceeds the trip value, the bimetallic contact starts heating up and bending away due to the different thermal rates of heat expansion within the contact. 

Eventually, the bimetallic contact bends to physically moving the trip bar and unlatching the contacts, causing an interruption in the circuit.

MCCB’s thermal protection will give a time delay to allow a short duration of overcurrent which is normally seen in some device operations, such as influx currents seen when starting motors. This time delay allows the circuit to continue the process even in these circumstances without tripping the MCCB.

• Electrical Fault Protection against Short Circuit Currents

MCCBs provide an instant and automated response to a short circuit or overcurrent fault since it works on electromagnetism. The MCCB generates a small electromagnetic field with a solenoid coil when the current passes through it. During routine operation, the solenoid coil generates the electromagnetic field in a nominal amount. However, a large current begins to flow through the solenoid coil during a short circuit fault, creating a strong electromagnetic field that attracts the trip bar and opens the contacts.

• Disconnection of Electrical Switch

In addition to automatic tripping, switches of MCCB can also be manually disconnected in the case of an emergency or to conduct maintenance operations. 

Application of MCCB

Here are some of the many applications of MCCBs-

• Welding machines
• Generators
• Protecting motors
• Capacitor banks
• Electric feeders