One day at work, I was suddenly asked a question: What's the difference between an air switch and a circuit breaker ? I was immediately stumped. I'm ashamed to admit that despite studying electrical engineering and using them frequently, I didn't understand the difference between the two. In my previous understanding, wasn't an air switch just a circuit breaker?
Naturally, another question came to mind: if they are the same thing, then why are there two different names? Is it like the everyday terms "potato" and "sweet potato" or "yellow potato" and "white potato"? With this question in mind, I looked up relevant information and then summarized and shared what I learned with everyone.
1: Circuit breaker
This thing is so common; you can find it on the main incoming line of any electrical cabinet. Life experience tells us that circuit breakers are used to cut off and connect circuits; of course, they can also automatically cut off faulty circuits. So, what is its true academic definition?
A circuit breaker is a switching device that can close, carry, and interrupt current under normal circuit conditions and close, carry, and interrupt current under abnormal circuit conditions within a specified time. It can play a protective role, prevent accidents from escalating, and ensure that faults at the end do not affect the upstream circuit, thereby ensuring the safe operation of the main system.
Those of you working in power distribution are probably familiar with those two guys in the picture above, right? One is commonly seen in the main distribution cabinet, and the other is commonly seen in the distribution substation.
Generally, circuit breakers consist of auxiliary contacts, alarm contacts, shunt trip units, undervoltage trip units, electric operating mechanisms/rotary operating handles/extended handles, and interlocking devices. In terms of the number of terminals, they are available in single-pole, 2-pole, 3-pole, and 4-pole configurations. For installation, there are plug-in, fixed, and drawer-type options. Regarding wiring methods, there are front-panel wiring, rear-panel wiring, plug-in, and drawer-type options. In terms of operating range, they can be divided into high-voltage circuit breakers (above 3KV) and low-voltage circuit breakers.
2: Air switch
Next, let's talk about the most common type of switch we see in daily life, the one found in every household—the air circuit breaker. This "brother" is so approachable; I imagine every household has several of them in their main electrical box. As shown in the picture below, do they look familiar? That's right, they are air circuit breakers [of course, there are also three air circuit breakers with residual current protection].
So, what is an air switch? It's a switch that automatically disconnects when the current in a circuit exceeds its rated current. It can both connect and disconnect circuits, providing protection against short circuits, severe overloads, and undervoltage in circuits or electrical equipment. Ultimately, it is, after all, a type of switch.
Generally, an air circuit breaker consists of auxiliary contacts, alarm contacts, shunt trip units, undervoltage trip units, an electric operating mechanism/rotary operating handle/extended handle, and a locking device. In terms of the number of terminals, there are single-pole, 2-pole, 3-pole, and 4-pole types. Regarding wiring methods, there are front-panel wiring, rear-panel wiring, plug-in type, and drawer type. In terms of tripping methods, there are three types: thermal tripping, electromagnetic tripping, and combined tripping. Its general internal structure is as follows:
From the above introduction, you might think they're all the same. You can't see any difference. Their internal components, wiring, and functions seem similar. So, are there any differences? The answer is yes.
3: Differences:
I've summarized the differences as follows:
First, there's the difference in voltage levels: air switches are generally suitable for voltage levels below 500V, while circuit breakers are typically used for voltage levels above 220V. This explains why air switches are almost never seen in high-voltage distribution cabinets.
Second, there is a difference in the ability to interrupt current: circuit breakers can withstand a wider range of loads and short-circuit currents than air switches.
Thirdly, there is a difference in the supporting equipment: the supporting equipment for the measurement, logic, and execution parts of circuit breakers is more complex.
Fourth: Differences in arc extinguishing medium and method: The arc extinguishing medium and method of circuit breakers include air circuit breakers, vacuum circuit breakers, oil-filled circuit breakers, and low-oil circuit breakers, etc.
From the four differences mentioned above, you've surely noticed that all the capabilities and ranges of an air switch fall within the scope of a circuit breaker. Yes, an air switch is actually a type of circuit breaker; its proper name should probably be air circuit breaker.
4. A side note:
The history of circuit breaker development: The world's first circuit breaker was invented in 1885. The air circuit breaker was invented in 1905. After 1930, the invention of various arc-extinguishing devices made circuit breakers more complex and increasingly sophisticated. More recently, electronic trip units and intelligent circuit breakers have emerged.
The circuit breaker problem: of course it tripped. There are two types: one is that it tripped when it shouldn't have, and the other is that it didn't trip when it should have. For the first type, the reason is relatively simple in my opinion: it's either exceeding the limit, the instantaneous peak value exceeding the limit, or something was missed…; for the second type, well, you probably won't even notice, right? By the time you do, there's probably already been a major accident. If it didn't trip when it should have, is it because it didn't exceed the limit (the selected circuit breaker was too large, or the wiring was too small), or is there a fault in the circuit breaker itself?
Do you read circuit diagrams yourself? Here are some symbols for power switches that might be helpful: power switch symbol Q, circuit breaker symbol QF, knife switch symbol QK, disconnector symbol QS.
