Is a circuit breaker an air switch?

Circuit Breakers vs. Air Switches: Clarifying the Relationship

A circuit breaker is a switching device capable of closing, carrying, and interrupting current under normal circuit conditions, and of closing, carrying for a specified time, and interrupting current under abnormal circuit conditions (such as short circuits). It is more than just a switch—it serves as a critical safety protection device. When a fault occurs in a power system, a circuit breaker can rapidly cut off the current in high-voltage circuits, preventing the situation from escalating and effectively safeguarding personnel and property.

In low-voltage electrical systems, the term "air switch" is often used interchangeably with "circuit breaker," implying its ability to interrupt short-circuit currents. However, high-voltage air switches belong to a different category. So, is a circuit breaker the same as an air switch?

The answer is no. Low-voltage circuit breakers are mainly classified into molded-case circuit breakers (MCCBs) and low-voltage power circuit breakers (LPCBs). The former is used for low-current applications, while the latter handles high-current systems. Among these, the molded-case circuit breaker is commonly known as an "automatic air switch" due to its widespread use.

According to China's national standard GB14048.2 (a mandatory standard—refer to it for detailed understanding of low-voltage circuit breakers), the following definitions apply:

• Circuit Breaker: A mechanical switching device capable of making, carrying, and breaking currents under normal circuit conditions, and of making, carrying for a specified time, and breaking currents under specified abnormal circuit conditions (e.g., short circuits).
• Molded-Case Circuit Breaker (MCCB): A circuit breaker with an enclosure made of molded insulating material, forming an integral part of the device.
• Air Circuit Breaker: A circuit breaker whose contacts open and close in atmospheric-pressure air.
• Vacuum Circuit Breaker: A circuit breaker whose contacts open and close within a high-vacuum chamber.

Since molded-case circuit breakers typically use air as the arc-quenching medium, they are colloquially referred to as "air switches." However, this term is technically imprecise. "Air switch" and "circuit breaker" represent different conceptual categories: an air switch refers to the arc-quenching medium, while a circuit breaker refers to the device's function and application. Therefore, an "air switch" is merely one type of circuit breaker implementation and should not be equated with the broader category of circuit breakers.