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The Purpose Of A Circuit Breaker

A circuit breaker is an electrical gadget whose primary role is to monitor the flow of current and prevent the occurrence of electrical mishaps. Usually, circuit breakers are located at or beside a building or space's power central distribution board. A circuit breaker contains a trip switch that trips it off when an overload, short circuit, or ground fault is detected in an electrical system.

Circuit breakers are designed to detect defects from electrical lines and cut off current supply from the faulted line. These gadgets are applied in various settings, including homes, offices, and industries. This article seeks to look into the essential components of a circuit breaker, how it works, the different types of circuit breakers, and the difference between a circuit breaker and a fuse box.

Fundamental Components Of A Circuit Breaker

Knowing how a circuit breaker works would help you to understand how it functions. But first, it is essential to look at the components of a standard circuit breaker.

Frame or shelf

This circuit breaker part serves as a protective panel for its internal components. The frame gives the circuit breaker box rigidity, support, and the strength it requires to handle the interruption process and realise the necessary current interruption ratings. In addition, it provides insulation by isolating the electrical current so as to protect both people and equipment during operation.

The frame of a circuit breaker is usually made of either a metallic material or a moulded insulated case.

Moulded case

These types of frames are made of strong insulating materials like thermostat composite resins (plastics) and glass polyester. Moulded cases are suitable for circuit breakers with low voltage power.

Insulated case

They are used in medium voltage circuit breakers.

Metal frame

They are made of well-measured pieces of metal. The metal pieces are fused and bolted together to make the frame. These frames are considered suitable for both high voltage circuit breakers and vacuum breakers with medium voltage.

Arc-fault circuit interrupter

An arc-fault circuit interrupter is also known as an arc chute or arc extinguisher. It is situated close to or near the movable contact arm. An arc refers to the discharge of electric current as it passes between two contacts. So long as there is a flow of electric current, the occurrence of an arc is inevitable.

An ideal arc-fault chute should prevent the heat from the arc from interfering with the functionality of the circuit breaker, thus preventing short circuits and fire hazards. In the power industries, aside from the arc fault circuit interrupter or chutes magnet coil, puffers and SF6 (sulphur hexafluoride) are used to manage and control electrical arc.

The contacts move when an arc fault occurs and is designed to safeguard against thermal overloads (overcurrent) and magnetic (short circuit) faults. In low voltage circuit breakers, the contacts are located inside the arc interruption chamber, while in vacuum circuit breakers with medium voltage, they are located inside the vacuum interruption compartment. Contacts help to ensure adequate flow of air inside the circuit breaker.

The contact assembly comprises three parts, the movable contact arm (arcing contact), the stationary conductor (auxiliary contact), and the fixed or primary contact. The movable contact arm transfers the arc into the arc-fault circuit interrupter chamber or the arc-chute. The stationary contact moves to close (make) or open (break) the circuit as the circuit breaker opens or closes.

Trip unit/trip switch

The trip switch enables the circuit breaker to perform its protective function. The primary role of a trip switch is to trigger the operating mechanism of the circuit breaker when it detects a power overload, short circuit, or other electrical faults. A trip unit can either be electromechanical or electronic.

Electronic trip units

They are also referred to as solid-state trip units. This type of trip switch or unit offers speciality protection for ground faults. However, they have features like programming monitoring, diagnostic communication, system coordination, and testing that are unavailable for thermal-magnetic trip units.

Electromechanical trip units

Circuit breakers mainly utilise this trip unit with low power voltage. Electromechanical trip units use bimetal and electromagnets to protect your electrical system against power overload and short circuits. This category of trip units does not offer options for ground fault protection and other special features.

Operating mechanism

This part is connected to the tripping mechanism of a circuit breaker. The operating system or mechanism helps to ensure that the circuit breaker is seamlessly accessible. The operating system of a circuit breaker is mainly of two types:

Two-step stored energy

This operating system or mechanism is utilised by circuit breakers that require a lot of energy to close. The two-step stored energy operating system charges the closing spring and releases energy to shut down the circuit breaker. This operating system allows for rapid re-closing of the circuit breaker.

This operating mechanism uses a separate opening and closing spring to achieve a seamless rapid re-closing of the circuit breaker. The closing spring can be manually charged with a charging handle or an electrical motor. This operating system is designed for the safety and protection of the operator.

Over toggle

Serves as a means to open and close the circuit breaker. This operating system uses a quick-make and quick-break mechanism to open and close the circuit breaker. This means the speed that the handle is pulled determines the speed at which the contacts snap closed or open.

In addition, the over toggle operating mechanism helps to indicate whether the circuit breaker is off or not and equally shows if the breaker is tripped or not.

How A Circuit Breaker Works

As mentioned before, when an electrical fault is detected, the circuit breaker trips automatically and shuts down the power supply to the affected line or wiring. Most electrical circuit breakers contain a simple switch that is either connected to an electromagnet or a bi-metallic strip.

When the circuit breaker is turned on, electrical current flows through the electromagnets to the moving contacts and then to the stationary contacts. The electrical current that flows through the electromagnet gets magnetised. Current overload increases the magnetic force of the electromagnets, while a decrease in electrical current lowers the magnetism.

When an electrical fault is detected, the electromagnet becomes well charged and strong enough to pull the metal lever connected to the trip switch. This process shifts the moving contact arm away from the stationary contact and causes the circuit breaker to snap off. The snapped or tripped breaker cuts off the flow of electricity in the affected line.

The high electrical current does not charge up or energise the electromagnets in the case of electrical circuit breakers that use bimetallic strips. Instead, it causes the bimetallic strip to bend and divert the contact linkage.

Note: Because each circuit breaker is made to trip at specific amperage loads, there are different-sized breakers in the box.

Types Of Circuit Breakers

Circuit breakers are sorted based on different criteria. Let's look at the classification of circuit breakers based on two criteria.

Classification based on the uses

Domestic circuit breaker

This category of circuit breakers is designed to protect the home or household electrical system. Plugging multiple high voltage devices like high-power light and electronic heaters can cause an overload and damage to your household electrical wiring. They help to prevent the occurrence of electrical accidents in your home. The single pole and double pole circuit is an example of a domestic circuit breaker.

Miniature circuit breaker (MCB)

This is a special kind of domestic circuit breaker that supports various current ratings. Miniature circuit breakers or MCB cannot be adjusted. MCB is typically used in low-voltage circuits of around 100A. They are standard circuit breakers that primarily protect circuits against electrical overload.

Ground fault circuit breaker (GFI)

This is a solid-state device that detects ground faults and trips. A ground fault usually occurs when an electrical device comes in contact with water or when the user is standing in water or close to water.

Ground fault circuit breakers' primary role is to protect against electrical shocks. GFI circuit breakers are commonly installed in the kitchen, laundry rooms, swimming pools, bathrooms, and other water plumbing spaces.

The moulded case circuit breaker (MCCB) is an example of a standard ground fault circuit breaker. MCCB is adjustable and supports higher ratings up to about 1000A and above. In addition to providing ground fault protection, MCCB equally safeguards the circuit.

Commercial or industrial circuit breaker

This circuit breaker is designed for extremely high voltage electrical installations. A standard commercial circuit breaker has the same working principle as a basic breaker. An advanced industrial or commercial circuit breaker uses a solid or digital state circuiting to sense and calculate the safety criteria for an electrical system. Circuit breakers designed for industrial use should meet the IEC standards for industrial breakers.

Classification based on the functionality

Power circuit breaker

These are installed directly to an electrical panel drawn straight from a generator or transformer.

Distribution circuit breaker

These are installed directly to a conductor that connects the distribution panel to other installation points.

Consumer circuit breaker

These are installed directly to the load or circuit board and located as close as possible to it. All circuit breakers, no matter where they are installed or located, protect the electrical wiring they are connected to.

Circuit Breaker Vs. Fuse Box

Circuit breakers are often confused with fuse boxes, with most people assuming that they are the same. However, the truth is although these two perform the same function (i.e., regulating the flow of electrical power and protection), they are different, and so are their roles. Circuit Breakers and fuse boxes are different in the following ways:

Fuse boxes

  • They cost less compared to circuit breakers.
  • They require a replacement after each electrical fault interruption.
  • They do not require any maintenance.
  • They don't offer optional protective features like ground fault protection.
  • They only open after the occurrence of an overcurrent.

Circuit breakers

  • They cost more when compared to fuses.
  • They tend to only require a reset after interrupting an overcurrent event.
  • They require maintenance.
  • They have multiple optional protective features like ground fault protection.
  • You can use a fuse box alongside a circuit breaker, but, in the absence of a circuit breaker, a fuse box alone is not strong enough to interrupt high voltage overload or short circuit events.

Here is a rundown of the functions of a circuit breaker:

  • It protects electrical wires and prevents the hot wire from starting up a fire.
  • It helps to isolate or distinguish loads.
  • It keeps the circuit board organised and enables the user to quickly identify what each wire feeds.
  • It protects electrical equipment and household appliances.
  • A circuit breaker allows you to manually cut off the flow of electrical current from the desired line or wiring.

Circuit Breaker Installation Or Repair Services

In a nutshell, circuit breakers are safety devices that serve as electricity regulators to protect electrical appliances, electrical outlets, and the entire electrical system of a building from damage. If you need circuit breaker installation or repair services, you can contact a reliable electrician near you to do the job for you. With an expert, you are guaranteed professional electrical services that you can trust. You can also ask them any questions you might have regarding what a circuit breaker does.

Electrical Licence NSW 252436C / QLD 78559
Air Cond & Refrigeration 15200655 / AU52000
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