About Molded Case Circuit Breaker or MCCB – Construction, Working | New Topic [2024]

In this note, we are going to learn About Molded Case Circuit Breaker or MCCB, also its Construction, Working Principle, Advantages, and Disadvantages as well. Welcome to Poly Notes Hub, an one stop solution for Diploma Engineering Notes for Polytechnic Students.

Author Name: Arun Paul.

What is Molded Case Circuit Breaker?

An electrical protection device called a Molded Case Circuit Breaker (MCCB) is used to prevent overloads and short circuits in electrical circuits. It is composed of an insulating material-molded casing that encloses the circuit breaker mechanism. MCCBs are frequently found in residential, commercial, and industrial electrical distribution networks.

Construction of Molded Case Circuit Breaker

Below we shows the Molded Case Circuit Breaker Diagram –

• Molded Case: MCCBs are contained in a molded insulating box, usually composed of thermosetting plastic with a high strength. The interior components are supported mechanically and electrically by this casing.
• Electromagnet: MCCBs employ an electromagnet as part of its trip mechanism. When a short circuit develops, the high current flowing through it creates a strong magnetic field that attracts the electromagnet. This attraction activates the trip mechanism, which opens the circuit and interrupts the current flow.
• Trip Bar: The trip bar is attached to the electromagnet and acts as a device to trip the circuit breaker. When the electromagnet is engaged due to a fault situation, such as a short circuit, it pulls the trip bar, releasing the latch mechanism that keeps the contacts closed. This enables the contacts to open and close the circuit.
• Bimetallic Strip: MCCBs also include a bimetallic strip as part of their overload protection system. The bimetallic strip is made up of two metals that have differing coefficients of thermal expansion and are bonded together. When current travels through the circuit, the electrical resistance causes the bimetallic strip to heat up. As the temperature rises, the bimetallic strip bends until it triggers the trip mechanism, which opens the circuit and prevents overheating.
• Closed Contacts: MCCBs feature contacts that are typically closed while the circuit breaker is in its regular operating mode. These connectors allow current to flow across the circuit continuously. When a fault situation occurs, such as an overload or short circuit, the trip mechanism forces the contacts open, disconnecting the circuit and interrupting the flow of current.

Working Principle of MCCB

A Molded Case Circuit Breaker (MCCB) works using a combination of electromechanical concepts. The MCCB’s molded container contains critical components such as an electromagnet, trip bar, bimetallic strip, and closed contacts. Under normal circumstances, the contacts remain closed, allowing electrical current to flow across the circuit uninterrupted. However, when an overload or short circuit occurs, the MCCB’s protective mechanisms activate.

The bimetallic strip warms up during overloads as a result of the circuit’s increased current flow. The bimetallic strip bends as it heats up, finally setting off the trip mechanism, which opens the contacts and breaks the circuit. When there is a short circuit, the high current creates a powerful magnetic field that draws the electromagnet in. The trip bar is pulled by this attraction, which releases the latch that is keeping the connections closed and opens the contacts.

In both cases, opening the contacts stops the current flow, so preventing harm or risk to the electrical circuit and any linked equipment. The MCCB can be manually reset to return to normal operation after the fault has been resolved. A combination of magnetic and thermal protection methods guarantees the dependability and safety of electrical systems that use MCCBs.

Advantages of MCCB

Below we listed some merits of MCCB or Molded Case Circuit Breakers –

1. Solid defense against short circuits and overloads.
2. Decreasing downtime through quick fault response.
3. Robust design for enduring dependability.
4. Simple manual reset for rapid recovery.
5. Available in various current ratings.

Disadvantages of MCCB

Below we listed some demerits of MCCB or Molded Case Circuit Breakers –

1. Limited sensitivity to specific defects
2. Higher initial cost and Bulky design.
3. Lack of advanced features.