What is Air Circuit Breaker?

An air circuit breaker, also known as ACB, is a electrical switching device which provide short circuit and overcurrent protection ranging between 800 amperes to 10K amperes to connected devices. These circuit breakers are commonly used for low voltage applications under 450V. At the household level, ACBs can be commonly found in distribution panels.

The ACB is specially designed to operate in the air as an arc extinguishing medium, which can be triggered by a certain amount of atmospheric pressure. Presently, the design of ACBs has vastly improved, allowing them to be available as switching gears that have higher durability, and are comparatively easier to install, maintain, and operate than the other different kinds of traditional circuit breaker models.

Applications of ACB

It is also widely utilized in various settings including transformers, generators, industrial plants, and capacitors, the ACB efficiently interrupts high current flows, safeguarding low voltage circuits. Particularly crucial in high-voltage or power supply operations, it plays a vital role in protecting machinery, especially motor systems, from current overflow. Sudden voltage surges can significantly impair overall plant productivity, making the ACB an essential component for smooth and safe operations.

How do ACBs work?

ACBs have contacts in the air, unlike conventional circuit breakers, and hence work much better against low-voltage interruptions over high-voltage ones.

These circuit breakers are generally provided with two pairs of contacts –
- 1) The main contact - made from metal copper and carries the current at a normal.
- 2) The arcing contact - made of carbon.
While the main contacts stay open, no arcing is detected in the main contacts. Arcing is initiated when the arcing contacts are separated, allowing currents with a low resistance to pass through.
All arcing contacts are provided with arc runners that help in opening or closing the circuit. As the low-resistance current moves along the circuit, thermal and electromagnetic effects cause the arc discharge to move upwards, finally entering the arc chute.
Once inside the arc chute, the arc cools down, lengthens, and splits. Finally, it is extinguished when there is no current flowing through the circuit.
The ACB also contains a brake box made from insulating and fire-proof material, which is divided into sections using barriers made from the same material. Each barrier contains a small conductive metallic element that ensures continuity between the arcs once they are split within the chute.

Unlike traditional circuit breakers, ACBs are not designed to prevent the restoration of arcing by interrupting the recovery voltage of the connected system. Instead, it works on a different working principle which takes into account the temperature of the arc plasma to operate.