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What is a circuit breaker?

A circuit breaker is an electrical switch designed to protect an electrical circuit from damage caused by overcurrent/overload or a short circuit. Its basic function is to interrupt current flow after protective relays detect a fault.

Types of Circuit Breaker

Circuit breakers are mainly classified based on rated voltages. Circuit breakers below rated voltage of 1000V are known as the low voltage circuit breakers and above 1000V are called the high voltage circuit breakers.

The most general way of classification of the circuit breaker is based on the medium of arc extinction. Such types of circuit breakers are as follows:

-      -  Oil Circuit Breaker

-       - Minimum Circuit Breaker

-        -Air Blast Circuit Breaker

-        -Sulphur Hexafluoride Circuit Breaker

-        -Vacuum Circuit Breaker

-        -Air Break Circuit Breaker

Circuit breaker components

Although low and medium voltage circuit breakers have unique designs that are specific to amperage, voltage, and application, five main components are universal across the different types of circuit breakers.

The five universal circuit breaker components are:

-        Frame – Protects internal parts of the circuit breaker from outside materials

-        Operating mechanism – Provides a means of opening and closing the circuit breaker

-        Contacts – Allows the current to flow through the circuit breaker when closed.

-        Arc extinguisher – Extinguishes an arc when the circuit breaker interrupts a fault.

Trip unit – Opens the operating mechanism in the event of a prolonged overload or short circuit.


Internally, circuit breakers are made up of pairs of metallic contacts, both fixed and moving, in addition to an operating coil.

Under normal conditions – closed circuit – these contacts are touching each other, allowing the flow of electric current. These moving contacts are held together thanks to mechanical pressure exerted by another mechanism – a spring or compressed air, for example.

This pressure on the moving contacts is possible thanks to the potential energy stored in the mentioned pressure mechanism. When an overload occurs in the electrical circuit, the operating coil is charged with energy, and a plunger connected to the mechanism of the moving contacts allows the energy stored in this mechanism to be released, allowing the moving contacts to separate as well.

As the moving contacts separate, the circuit inside the CB (circuit breaker) opens, interrupting the flow of current and protecting the system from further damage.

However, it is important that you also understand the concept of “arc”.

When electrical current passes through an air gap from an energized component to a neutral component, a plasma discharge known as arc occurs. As an example, lightning is a very large arc, crossing atmospheric space from a cloud to the ground or another cloud.

Arcing can also occur in household electrical wiring, but also within circuit breakers during operation, which can damage them and cause fires if the arc is not controlled.

Therefore, the mechanism of circuit breakers also seeks to prevent or control, as much as possible, the generation of these electric arcs.

Circuit breakers alone cannot guarantee 100% of the safety of an electrical system. For that reason, some components can – and sometimes should – be added to electrical circuits to further improve the overall level of protection e.g., a surge arrester.

The fundamental function of circuit breakers is to constantly “verify” that the electrical charge does not exceed the safety limits and if so, stop the operation of the electrical circuit automatically, to avoid damage to the electrical installation in general.

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