What are the differences between air circuit breakers and isolation switches?

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Air circuit breakers and isolation switches are two different electrical devices that play different roles in electrical circuits. Their main differences are as follows:

### Functional Roles - **Air Circuit Breakers**: They are mainly used to automatically cut off the circuit under normal and fault conditions, providing protection against overload, short circuit and other issues for the circuits and equipment. When the current in the circuit exceeds the rated current of the air circuit breaker or a short circuit occurs, the thermal release or electromagnetic release inside the air circuit breaker will actuate, causing the contacts to open and cut off the circuit, thus protecting the lines and equipment from the damage caused by overload and short-circuit currents.

- **Isolation Switches**: They are mainly used to isolate the power source to ensure the safety of maintenance. When carrying out inspection, maintenance or replacement of electrical equipment, the isolation switch is opened to create an obvious break point between the equipment to be maintained and the power source, ensuring the safety of maintenance personnel during the operation process and preventing electric shock accidents caused by misoperation or unexpected power supply.

### Working Principles - **Air Circuit Breakers**: They work based on the principles of electromagnetic induction and thermal effect. When the current in the circuit is too large, sufficient electromagnetic force will be generated through the coil of the electromagnetic release, causing the tripping mechanism to actuate. Or when the current is overloaded, the thermal element will generate heat, and the bimetallic strip will bend and deform due to the heat, pushing the tripping mechanism to actuate, thus realizing automatic tripping to cut off the circuit.

- **Isolation Switches**: Their working principle is relatively simple. Mainly through manual operation of the knife switch, the contacts are switched between the closed and open positions to achieve the connection and disconnection of the circuit. In the closed state, the contacts are in close contact and the current is conducted through the contacts. In the open state, an obvious disconnection gap is formed between the contacts to isolate the power source.

### Structural Characteristics

- **Air Circuit Breakers**: They have a relatively complex internal structure, usually including contact systems, arc extinguishing systems, releases, operating mechanisms and other parts. The arc extinguishing system is used to extinguish the arc when the contacts are opened, reducing the erosion of the contacts by the arc and the impact on the circuit. The releases can be divided into thermal releases, electromagnetic releases and so on according to different protection functions.

- **Isolation Switches**: Their structure is relatively simple, mainly composed of knife switches, contacts, insulating pillars, operating mechanisms and so on. The knife switch is generally made of metal and fixed on the bracket through the insulating pillar. The operating mechanism is used to realize the opening and closing operations of the knife switch.

### Rated Current and Breaking Capacity

- **Air Circuit Breakers**: The rated current is usually selected according to the load current of the circuit, generally ranging from a few amperes to several thousand amperes. Their breaking capacity is relatively strong, and they can quickly cut off the circuit in the event of a short-circuit fault. The ability to break short-circuit currents is usually between several thousand amperes and dozens of thousand amperes.

- **Isolation Switches**: The rated current is also determined according to the actual application scenarios, but they are generally not used to cut off the normal working current and short-circuit current. Their breaking capacity is usually weak, and they are mainly operated under the condition of no current or extremely small current.

### Application Scenarios

- **Air Circuit Breakers**: They are widely used in various low-voltage distribution systems, lighting circuits, power circuits and so on. As overload and short-circuit protection devices for circuits, they are used in conjunction with other electrical equipment to ensure the safe operation of the circuits.

- **Isolation Switches**: They are mainly applied to power source isolation in substations, distribution rooms, factory workshops and other places. They play the role of isolating the power source in the processes of equipment inspection, maintenance, power outage operations and so on, and are often used in conjunction with circuit breakers, fuses and other equipment.