Circuit Breakers Fundamentals | Most Important 5 Components

What is Electrical Circuit Breaker?

Electrical circuit breakers are like a switching device, which is installed and used for safety purposes in all electrical fields like residential, commercial, and industrial. They have activated automatically as well as manually to control and protect an electrical power system.

There are different types of circuit breakers, which are used at different levels depending on the current carrying capacity, breaking capacity, and other functions.


What is Circuit Breaker(CB)?

A circuit breaker(CB) is a device used in the electrical power system. It can be controlled manually or remotely under normal and fault functions. It breaks a circuit automatically under fault conditions like overcurrent/overload, short circuit, etc.

electrical circuit breakers

Difference between Overcurrent, Overload, and Short Circuits

Overcurrent is defined as the excess of rated current. Overcurrent occurs due to overload, short-circuit, or ground fault. The effects of overcurrent include fire, conductor insulation damage, and equipment damage.

Overload is the operation of equipment in excess of normal, full-load rating or of a conductor in excess of rated ampacity. An overload is NOT a short-circuit or ground fault.

Short Circuit is an overcurrent which greatly exceeds the normal full load current of the circuit. A short circuit is an overcurrent but not an overload.


Circuit Breakers vs Fuse

The purpose of circuit breakers and fuse are the same, but there are some fundamentals differences that are important while making a decision to use it.

Fuses Circuit Breakers
  • It must be replaced after it has interrupted an overcurrent event.
  • It has a less initial cost.
  • No maintenance required.
  • Only opens on overcurrent events.
  • It can be reset after interrupting an overcurrent event.
  • It has a higher initial cost.
  • Regular maintenance required.
  • Optional protective features like Ground-Fault.

Components of Circuit Breakers

circuit breakers

image reference from eaton.com

There are mainly five components that play an important role in the electrical circuit breakers.

1) Frame

The frame protects all the internal parts of the circuit breaker and also supports the components. The frame provides insulation to contain the arc.

2) Operating Mechanism

It opens or closes contacts of the circuit breaker.

3) Contacts

The contacts allow the current to flow through a circuit breaker when it is closed.

4) Arc Extinguisher

It extinguishes the arc while in fault conditions.

5) Trip Unit

The trip unit senses the abnormal current flow in the event of overcurrent/overload, short circuit,

and causes the operating mechanism to open the contacts.


Types of Circuit Breakers

There are different types of circuit breakers, which are used at different levels depending on the current carrying capacity, breaking capacity, and other functions.

Miniature Circuit Breaker(MCB):

MCB stands for Miniature Circuit Breaker. MCB is an electromechanical device that is used to isolate the electrical circuit during overcurrent and short circuit situations. MCB is a resettable protective device without the use of the fusible element.

In simple words, MCB’s function is to interrupt the electrical flow during an error event. MCB is better than fuse since it doesn’t require to replace when an overload or short circuit identified.

circuit breaker

MCB is used for low power domestic and industrial applications. MCB works in a combination of a switch, overcurrent, and short circuit protection. There is a bimetallic strip to protect an overload condition and a solenoid to protect a short circuit.

MCB can be of two, three, and four poles with a neutral pole if necessary. MCB can work from 0.5 to 63Amp with a short circuit current range of 3 to 10000 Amp and can be work with 230 or 440 volts.

Molded Case Circuit Breaker(MCCB):

MCCB stands for Molded Case Circuit Breaker. MCCB is also an electromechanical device that is used to protect the circuit from over current and short circuit protection. MCCB is used when the load current exceeds the capability of a miniature circuit breaker, it is also used in the applications that require an adjustable trip current setting.

circuit breaker

A molded case circuit breaker(MCCB) is a device that can be used with a wide range of voltages. The main difference between MCCB and MCB is that the current ranges of MCCB are up to 2000 Amps and its trip setting is adjustable. The functions of MCCB are:

  • Overload Protection
  • Short circuit fault or ground fault
  • As a switch ON/OFF circuit.

MCCBs are available with a minimum current rating of 15Amps to a maximum current rating of 2000 Amps. The wide range of current allows them to be used in various applications in both low-power as well as high-power applications.

Earth Leakage Circuit Breaker(ELCB):

Earth Leakage Circuit Breaker usually abbreviated as ELCB, widely used in commercial as well as industrial applications. If there is a current leak due to insulation failure, ELCB is used to detect and prevent this condition and prevent injury to the human body or animal from electrical shock.

circuit breaker

ELCB detects the earth leaks current and isolates the electrical power flow by just tripping the circuit breaker. The working principle of ELCB is quite simple, There is a relay coil inside the ELCB. One terminal of this relay coil is connected to the metal body of the equipment and another terminal is connected directly to the earth.

When there is an insulation failure or any other fault that forces the current to flow from the metal body or the equipment to the ground. When the voltage difference across the relay crosses a predefined limit, it energizes the relay which results in the tripping of a circuit breaker to turn off the power supply to the equipment and stay off until reset by manually.

Residual Current Circuit Breaker(RCCB):

Residual Current Circuit Breaker(RCCB) is used to prevent injury from electrical shock to the human body. Basically, it isolates the electrical power supply in a fraction of seconds when there is a fault condition occurs.

circuit breaker

The working principle of RCCB is very simple, as per the Kirchhoff’s current law state that the incoming and outgoing current must be equal in the circuit. This circuit breaker identifies the unbalance current or current difference between the incoming and outgoing due to fault conditions.

The circuit breaker is designed in such a way that it compares the value of incoming and outgoing circuit current. Whenever there is a difference that is in mA, the residual current which is basically the difference between the two currents actuates the circuit to trip/switch off.


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