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.
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.
The tripping mechanism of a switch is a linkage device. When the main contacts are closed by the operating mechanism, they are locked in the closed position by a latch. If a fault occurs in the circuit, the relevant trip unit will activate, causing the latch in the tripping mechanism to disengage, and the main contacts will then quickly disconnect under the action of the release spring. According to their different protective functions, trip units can be divided into overcurrent trip units and undervoltage trip units, among others.
Under normal circumstances, the armature of the overcurrent trip unit is released. In the event of a severe overload or short circuit, the coil connected in series with the main circuit generates a strong electromagnetic force that pulls the armature downwards, releasing the latch and causing the main contacts to open. The undervoltage trip unit operates in the opposite manner. When the voltage is normal, the electromagnetic force holds the armature, allowing the main contacts to close. If the voltage drops significantly or power is lost, the armature is released, causing the main contacts to open. When the power supply voltage returns to normal, the circuit breaker must be reset before the unit can operate, thus providing undervoltage protection.
The main differences between air circuit breakers and residual current circuit breakers (RCCBs) lie in their operating principles, protected objects, functions, application ranges, appearance, and models. Details are as follows:
The operating principles are different. An air circuit breaker uses a mechanical device or electromagnetic mechanism to detect the magnitude and changes in current in the circuit. When the current in the circuit exceeds a set value or an abnormal situation such as a short circuit occurs, the air circuit breaker will automatically cut off the circuit. A residual current circuit breaker (RCCB) provides protection by detecting leakage current in the circuit. When the leakage current in the circuit exceeds a set value, the RCCB will immediately cut off the circuit.
The objects they protect are different. Air circuit breakers are mainly used to protect electrical equipment, such as motors and power lines, to prevent equipment damage or fire accidents; residual current circuit breakers are mainly used to protect personal safety. When a leakage accident occurs, they can quickly cut off the power supply to prevent electric shock accidents.
They have different functions. The main function of an air circuit breaker is to provide overload and short-circuit protection; the main function of a residual current circuit breaker is to provide leakage protection.
The applications differ. Circuit breakers are widely used in industrial and civil electrical equipment; residual current circuit breakers are mainly used in low-voltage power distribution systems and household electricity, as well as in places where personal safety requirements are high.
They differ in appearance and model number. Air circuit breakers are usually equipped with a handle for controlling the opening and closing of the circuit; some models of residual current circuit breakers may be marked with "DZ" or "LE".
The installation locations differ. Circuit breakers are typically installed in electrical equipment such as distribution boxes and power supplies; residual current circuit breakers (RCCBs) are typically installed in electrical equipment such as sockets and lighting fixtures in homes.
The detection methods differ. An air circuit breaker trips when the current between the live and neutral wires is too high; a residual current device (RCD) trips when a human body forms a circuit with the ground after touching the live wire.
In summary, circuit breakers are mainly used to protect electrical equipment and prevent overloads and short circuits; while residual current circuit breakers are mainly used to protect personal safety and detect and prevent leakage current.
