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Circuit Breaker – Definition, Functioning and Types

Sep 6, 2022

An electrical circuit breaker is a switching mechanism for managing and safeguarding an electrical power system used manually and automatically. It is designed to safely interrupt the arc created during the shutting of a circuit breaker since the current power system deals with extremely high currents. 

The vast power network and numerous electrical devices it is coupled with make up the current power system. A robust fault current will pass through this equipment and the power network during a short circuit or any other electrical fault (such as electric cable problems). The networks and equipment may sustain long-term harm from this high current.


The fault current needs to be eliminated as soon as possible from the system to protect these items of machinery and the power networks to send dependable, high-quality power to the receiving ends. The system must quickly return to regular operation when the problem is fixed. In addition, many switching activities must be carried out for the power system to be adequately controlled.

Therefore, there must be a unique switching device that can be operated securely under enormous current carrying conditions to quickly disconnect and reconnect various elements of the power system network for protection and management.


Significant arcing would occur between switching contacts during the cessation of a large current. Hence care should be taken to quench these arcs in circuit breakers safely. It is a unique device that performs all necessary switching activities while electricity flows.

What is a Circuit Breaker? 

A circuit breaker is defined as a switching device that interrupts the erroneous current and serves as a switch to safeguard the electrical system.


The Functioning of a Circuit Breaker

Circuit Breaker

Fixed contacts and movable contacts make up most of the circuit breaker. These two contacts are physically linked to one another while the circuit breaker is in its typical “ON” state due to the mechanical pressure exerted on the moving contacts. When a switching signal applies to a circuit breaker, the potential energy accumulated in the working mechanism is released.


The potential energy can be stored in the circuit breaker in various methods, including via hydraulic pressure, compressed air, or deforming metal springs. However, potential energy must be released during operation, regardless of the source. The moving contact slides thanks to the release of potential energy quickly.

When a switching pulse energises a circuit breaker’s working coils (tripping coils and closure coils) and displaces the plunger inside, the circuit breaker trips, this operating coil plunger is typically connected to the circuit breaker’s operating mechanism. As a result, mechanically stored potential energy in the breaker mechanism is released as kinetic.


The energy causes the moving contacts to move because they are mechanically connected to the operating mechanism through a gear lever arrangement.

After a circuit breaker cycle, the whole energy saved is released, and potential energy is once again stored in the functioning mechanism of the circuit breaker using a spring charging motor, an air compressor, or any other method.


We have so far talked about the mechanical operation of a circuit breaker. However, while discussing how it operates, it is also essential to consider its electrical properties. Let’s talk about the electrical theory behind circuit breakers.

It must handle immense rated power or experience a failure. Due to this significant power, the arcing between the circuit breaker’s moving, and fixed contacts are at dangerously high levels. As we previously explained, if the dielectric strength between the circuit breaker’s current-carrying contacts proliferates during each alternating current zero crossing, the arc in the circuit breaker can be safely quenched.


There are several ways to increase the dielectric strength of the media between contacts, including compressing the ionised arcing media because doing so speeds up the deionisation process of the press, cooling the arcing media because doing so increases the resistance of the arcing path, or replacing the ionised arcing media with new gases. Therefore, the operation of the circuit breaker should include some arc quenching operations.

Even though they work autonomously and without supervision, remote circuit breakers allow on-demand remote control operation.

Moulded Case Circuit Breakers

Circuit Breaker

It is essential for system designers and installers to comprehend the workings of moulded case circuit breakers and the significance of their ratings as installed system capacity in the Australian PV market keeps growing.

An electrical protection device known as a moulded case circuit breaker (MCCB) is used to safeguard an electrical circuit against excessive current, which can result in an overload or short circuit. MCCBs have changeable trip settings and a current rating of up to 2500A, making them suitable for a variety of voltages and frequencies. For system isolation and protection, these breakers are utilised in place of tiny circuit breakers (MCBs) in large-scale PV systems.

How the MCCB functions

To offer the trip mechanism for isolation and protection, the MCCB combines a thermal element, which is temperature sensitive, with a magnetic element, which is current sensitive. As a result, the MCCB can offer:

  • Protection against overload
  • electrical short circuit protection 
  • electrical switch for disconnecting.

Protection from overload

The temperature-sensitive component of the MCCB uses overload protection. This part is basically a bimetallic contact, which is a contact made of two metals that expand at different rates when heated. The bimetallic contact will enable electric current to pass through the MCCB under typical working circumstances. Due to the various thermal rates of heat expansion within the contact, the bimetallic contact will begin to heat up and bend away when the current reaches the trip threshold. The contact will eventually bend to the point where it physically pushes the trip bar and unlatches the contacts, interrupting the circuit.

In order to accommodate a brief period of overcurrent that is frequently observed during the operation of particular devices, such as inrush currents experienced while starting motors, the thermal protection of the MCCB will generally incorporate a time delay. Due to the time delay, the circuit is able to function normally under these conditions without tripping the MCCB.

Amount of the MCCB

An electrical circuit’s projected operating current and potential fault currents should be used to size the MCCBs. When choosing MCCBs, there are three key considerations:

  • The system voltage should be comparable to the MCCB’s rated operating voltage.
  • The MCCB’s trip value has to be modified to account for the load’s current draw.
  • The theoretically conceivable fault currents must be greater than the MCCB’s breaking capability.

Types of Circuit Breaker 

Different types of circuit breakers exist based on various parameters. It can be classified into the following groups based on its arc quenching media.

  • Circuit breaker for oil.
  • Circuit breaker for air.
  • Circuit breaker for SF6.
  • Circuit breaker for vacuum.

A circuit breaker has two essential contacts:  

1) Fixed contacts

2) Moving contacts

Circuit breaker for low voltage. 

  • Outside breaker. 
  • Indoor breaker.

The following categories of circuit breakers may be made based on how they function:

  • A circuit breaker with a spring mechanism.
  • Air-powered circuit breaker.
  • It is hydraulic.

Circuit breaker types are categorised based on the installation’s voltage level as follows:

  • Circuit breaker for high voltage.
  • Circuit breaker for medium voltage.
  • Circuit breaker for low voltage.

Frequently Asked Questions

1. What is the process of a circuit breaker finder?

A receiver and transmitter are used in the operation of a circuit breaker finder. A signal from the transmitter travels through the wire and is received at the circuit breaker. The receiver will then pick up that precise signal by way of a particular circuit breaker finder.

Usually, a transmitter and receiver are offered together. If you use a different device that wasn’t included in the original package, especially one from a different manufacturer, it might not function.

When maintaining an outlet or light fixture, especially if you are replacing a circuit breaker, the panel lacks labelling, you must use this equipment. You may quickly and safely turn off the area you need to work on by finding the right breaker for the circuit you’re fixing.

2. What is a circuit breaker used for?

These are primarily used to switch various types of loads in industries, buildings, commercial complexes, and hotels, among other places.

3. Why replace a circuit breaker?

When replacing a circuit breaker, identify the brand, kind, and size of the breaker, you’ll be replaced with before you start the replacement. The rights to the circuit breakers are owned by the manufacturer of the specific circuit breaker panel you have. For instance, Square D QO and Homeline are two well-liked breaker panel designs that only accept breakers built for their panels. A thin-line breaker produced by GE is also only appropriate for specific GE panels. Despite the fact that a range of breaker types may be installed in panels from various manufacturers, you shouldn’t mix and match them unless they have been tested and approved for use.

4. How to prevent electrical short circuit currents?

MCCBs respond instantly to a short circuit problem based on the electromagnetic principle based on the electromagnetic principle. When electricity flows through the MCCB, a solenoid coil inside the device produces a modest electromagnetic field. The electromagnetic field produced by the solenoid coil is hardly noticeable when it is functioning normally. A short circuit failure in the circuit, however, causes a significant current to start flowing through the solenoid. As a result, a powerful electromagnetic field is created, drawing the trip bar and opening the contacts.

5. What is in a circuit breaker?

There is a spring and a small solder piece hooked inside each circuit breaker (a melt-able fusible alloy). A wire that travels through your house is connected to each circuit breaker. Soldier is a conductor of the electricity that powers your home.

6. What are main types of MCB?

There are various MCB types available, including types A, B, C, D, K, and Z. Type B, type C, and type D are the three essential variations, though. Each is made to respond to the potential strength of electrical surges in various environments.

7. What does MCCB mean?

A moulded case circuit breaker (MCCB) is an electrical protection device that is used to protect an electrical circuit from excessive current, which can cause overload or short circuits. 

Circuit Breaker


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