Air switches, circuit breakers , and residual current devices (RCDs) are all familiar to most people. However, even those in the electrical field might not be able to clearly explain how they are used, their characteristics, and their differences. Today, let's learn about them together!
1. Air switch
An air switch, also known as an air circuit breaker, is a type of circuit breaker. It is a switch that automatically disconnects when the current in the circuit exceeds the rated current. Air switches are a very important electrical appliance in low-voltage power distribution networks and electric drive systems, integrating control and multiple protection functions. In addition to connecting and disconnecting circuits, it can also protect against short circuits, severe overloads, and undervoltage in circuits or electrical equipment, and can also be used for infrequent starting of motors.
There are three types of tripping methods: thermal, electromagnetic, and combined tripping.
When a general overload occurs in the circuit, the overload current, while insufficient to trip the electromagnetic trip unit, generates heat in the heating element, causing the bimetallic strip to bend upwards and push the lever to disengage the latch, thus breaking the main contacts and cutting off the power supply. When a short circuit or severe overload occurs, the short-circuit current exceeds the instantaneous trip setting current value. The electromagnetic trip unit generates a sufficiently large attraction force, drawing the armature in and striking the lever. This causes the latch to rotate upwards around the pivot and disengage from the latch. Under the action of the return spring, the latch breaks the three main contacts, cutting off the power supply.
II. Circuit Breaker
A circuit breaker is a switching device capable of closing, carrying, and interrupting current under normal circuit conditions, and capable of closing, carrying, and interrupting current under abnormal circuit conditions within a specified time. Circuit breakers are classified into high-voltage circuit breakers and low-voltage circuit breakers according to their application range. The boundary between high and low voltage is somewhat blurred; generally, circuit breakers above 3kV are referred to as high-voltage electrical appliances.
Circuit breakers are used to distribute electrical energy, infrequently start asynchronous motors, and protect power lines and motors. They automatically disconnect the circuit when severe overloads, short circuits, or undervoltage faults occur, functioning similarly to a combination of a fuse switch and over/under-temperature relays. Furthermore, they generally do not require component replacement after interrupting a fault current. Currently, they are widely used.
In the generation, transmission, and use of electricity, power distribution is an extremely important link. The power distribution system includes transformers and various high- and low-voltage electrical equipment, with low-voltage circuit breakers being a widely used electrical appliance.
According to the number of poles: there are single pole, two pole, three pole and four pole, etc.;
According to the installation method, there are insert type, fixed type and drawer type, etc.
Product Introduction: A9/EC65 Miniature Circuit Breaker: Lighting power distribution circuit, short circuit and overload protection.
III. Residual Current Device
A residual current device (RCD), also known as a residual current circuit breaker, is mainly used to protect equipment from leakage faults and to protect people from fatal electric shocks. It has overload and short circuit protection functions and can be used to protect circuits or motors from overload and short circuits. It can also be used for infrequent switching and starting of circuits under normal conditions.
Residual current devices (RCDs) can be classified according to their protection function, structural features, installation method, operation mode, number of poles and wires, and operating sensitivity. Here, we mainly describe them according to their protection function and application. Generally, they can be divided into three types: residual current relays, residual current switches, and residual current sockets.
IV. Differences among the three
4.1 Difference between circuit breakers and air switches
Difference in voltage levels: Generally, air switches are suitable for voltage levels below 500V, while circuit breakers can usually be used for voltage levels above 220V.
The ability to interrupt current differs: general circuit breakers can withstand greater loads and short-circuit currents.
Differences in arc extinguishing medium and method: Circuit breakers use not only air circuit breakers, but also vacuum circuit breakers, oil-filled circuit breakers, low-oil circuit breakers, sulfur hexafluoride circuit breakers, etc.
Differences in supporting equipment: Generally speaking, the equipment supporting the measurement, logic and execution mechanisms of circuit breakers is more complex than that of air circuit breakers.
4.2 Advantages and disadvantages of air switches, circuit breakers, and residual current devices (RCDs)
1. A 2-pole circuit breaker is preferable, as it disconnects both the live and neutral wires simultaneously to prevent danger caused by reverse connection. A 1-pole circuit breaker with a neutral wire that is always connected is dangerous if accidentally reversed.
2. Electromagnetic residual current devices (RCDs) perform better than electronic ones, but they are more expensive, have a more complex structure, and are more fragile. They cannot withstand the bumps and knocks of long-distance transportation and rough handling during express delivery. Be cautious when buying imported ones.
3. Domestically produced circuit breakers may have slightly inferior residual current protection compared to imported ones, but their overload protection is still very reliable. Their price is lower than imported circuit breakers without residual current protection, and even if the residual current protection fails, they should still be reliable as circuit breakers on their own.
