All you need to know about ACBs and MCBs

In the era of technology and automation, there are so many instances where unanticipated mishaps can occur. These calamities can lead to significant damage to physical infrastructure such as offices, homes, schools, industries, etc. An eminent example of such a mishap is during a short-circuit or any other similar type of electrical contingency (electric cable faults) i.e when high-fault current passes through the equipment along with the power network grid itself. This high current can potentially damage the equipment connected in the respective power management system and the networks enduringly. Removing these faulty currents from the grid as fast as possible is an effective measure to safeguard devices which could be impacted. Even when this is done, the system has to be restored to its optimal functionality swiftly in order to supply a dependable quality of power.

There are a few unique types of devices that can promote building management safety and control under unfavourable current-carrying conditions. These devices are commonly referred to as circuit breakers: a unique appliance which carries out the function of switching operations during current-carrying conditions. These types of circuit power breaker can be elaborated as below.

Air Circuit Breaker (ACB)

This type of circuit breaker, which operates in the air at atmospheric pressure, is coined as an Air Circuit Breaker. Over the past few years, these breakers have entirely replaced oil circuit breakers. Their process of arc quenching control is in fact quite unique in comparison to the functioning of oil circuit-breakers. In most cases, they are generally implemented for low-voltage interruption.

How do Air Circuit Breakers (ACB) work?

The working of an air circuit breaker involves several key components: contacts, arc extinguishing chamber, operating mechanism, and control system. When the electrical current is within safe limits, the contacts inside the ACB remain closed, allowing power to flow uninterrupted. However, when an overload or short circuit occurs, the current rises beyond the set threshold, and the operating mechanism triggers the separation of contacts.

As the contacts separate, an electrical arc forms between them due to the high current flow. The air circuit breaker uses compressed air or ambient air to cool and extinguish this arc quickly. Modern ACBs often feature arc chutes, metal plates or compartments that guide and divide the arc, dissipating its energy safely. This mechanism ensures minimal damage to the breaker and prevents fire hazards.

The ACB can be operated manually for routine maintenance or automatically during faults. Its control system often integrates with protective relays and sensors to detect abnormal conditions and initiate a trip signal. After a fault is cleared, the air circuit breaker can be reset to restore normal power flow.

Key components of an Air Circuit Breaker (ACB)

An air circuit breaker (ACB) consists of several essential components that work together to ensure effective protection and reliable operation of electrical systems:

• Contacts: These are the conductive parts that carry the current under normal conditions. They separate during a fault to interrupt the flow of electricity.
• Arc extinguishing chamber: This component safely dissipates the electrical arc formed when contacts open. Arc chutes or plates are used to cool and divide the arc, ensuring rapid extinction.
• Operating mechanism: Responsible for opening and closing the contacts. Can be operated manually or automatically during fault conditions.
• Control system: Works with protective relays and sensors to detect abnormal currents. Sends trip signals to the operating mechanism to interrupt power when needed.
• Current and voltage sensors: Monitor the electrical parameters continuously. Ensure the ACB responds accurately to overloads or short circuits.
• Frame and insulation: Provides structural support and prevents accidental contact with live parts. Ensures safe operation even in high-voltage environments.

These components collectively enable the air circuit breaker to protect electrical circuits efficiently, manage high currents, and maintain reliable power distribution in industrial and commercial setups.

Applications of Air Circuit Breakers

Air Circuit Breakers (ACBs) are widely used in electrical systems due to their reliability, high interrupting capacity, and ability to handle frequent switching operations. One of their primary applications is in industrial plants where heavy machinery and motors require protection from overloads and short circuits. In such settings, ACBs help prevent damage to equipment and ensure continuous production without unexpected downtime.

ACBs are also essential in commercial buildings and high-rise structures, where multiple electrical loads need coordinated protection. They safeguard power distribution networks from faults and maintain operational stability. Additionally, ACBs are commonly used in power distribution substations, controlling and protecting medium-voltage circuits and ensuring the safety of personnel and equipment during abnormal conditions.

Another important application is in renewable energy systems, such as solar and wind power installations. ACBs can manage high current fluctuations and isolate faulty circuits efficiently, improving system reliability. They are also used in critical facilities like data centres, hospitals, and airports, where uninterrupted power supply and rapid fault isolation are crucial.

Miniature Circuit Breaker (MCB)

A Miniature Circuit Breaker is one of the most popular devices used to protect electrical appliances from potential damages in the case of power distribution. Using an MCB is generally reliable and safe, as opposed to a fuse. Swift restoration of electrical supply is a possibility opposite to a fuse – a one-time device that eventually needs replacement after performing its function. One of the primary features of an MCB which enhances its capabilities and applicability is the fact that their functionality can be restored with the slightest effort. To do this, one just needs to push the knob of the miniature circuit breakers back to the ‘on’ position. Compare this to the performance of a fuse – after carrying out its function, it needs to be replaced completely.

Difference between ACBs and MCBs

Air Circuit Breakers and Miniature Circuit Breakers are both designed to protect electrical circuits, but they differ significantly in their construction, applications, and capacity. ACBs are used for high-voltage and high-current circuits, typically in industrial and commercial settings. They can handle large loads, frequent switching, and have higher interrupting capacity, making them suitable for protecting transformers, generators, and main distribution lines.

On the other hand, MCBs are designed for low-voltage residential or commercial circuits. They protect wiring and smaller appliances from overloads and short circuits but are not suitable for handling very high currents. MCBs are compact, easy to install, and commonly used in homes and small offices.

Another key difference is in the mechanism of operation. ACBs often use air as the arc-extinguishing medium and can be manually or electrically operated, with options for advanced protection features like adjustable trip settings. MCBs operate automatically and trip instantly when current exceeds a predefined limit, but they lack the advanced control and monitoring capabilities of ACBs.

Finally, ACBs are more expensive due to their higher capacity and complex design, while MCBs are cost-effective for small-scale applications.

Related Article : What are Miniature Circuit Breakers (MCBs)?