Abstract: Electrical fire accidents are serious disasters faced by mankind. Their occurrence is unpredictable and can be said to be one of the most devastating disasters to cause human losses. Keywords: Electrical fire automatic protection circuit breaker For many ordinary civil buildings, such as factories, schools, hospitals, shopping malls and various public entertainment venues, effective measures should be taken to prevent fires as much as possible. Even if a fire does occur, the losses caused by the fire should be minimized. At the same time, the most common means at the scene of a fire should be to immediately cut off the power supply to prevent secondary injuries to firefighters after electric shock. This is a solution that people have been trying to find. If a simple method that is economical, practical and easy to popularize can be adopted for the prevention, monitoring and automatic protection of fire disasters, it will provide powerful assistance to fire prevention work. 1 Working principle and application The electrical fire automatic protection circuit breaker is based on the existing ordinary residual current circuit breaker, equipped with a temperature sensing element that changes monotonically with the external temperature - thermistor. The circuit breaker has corresponding electronic circuitry inside. When the ambient temperature rises abnormally, exceeding a certain normal temperature range (defined as the rated operating temperature), the electronic circuitry automatically drives the main contact trip unit of the automatic fire protection circuit breaker to disconnect the circuit on the load side, preventing insulation damage to the load side circuits and equipment due to an electrical fire and subsequent short circuit accidents. The automatic fire protection circuit breaker will not trip below the lower limit of the specified temperature range, regardless of the duration; this is the rated non-operating temperature. The rated non-operating temperature ensures that the automatic fire protection circuit breaker will not malfunction due to normal ambient temperature increases or accidental heat sources, ensuring its reliable operation. Therefore, for an automatic fire protection circuit breaker to respond correctly to a fire, the most important factor during installation is ensuring that the thermal element on the circuit breaker, i.e., the fire detection probe, can directly sense temperature changes in the monitored space. There must be no objects directly in front of the probe that could affect the direct radiant transfer of temperature. If the automatic fire protection circuit breaker is installed inside a lighting box, and the temperature changes in the monitored area cannot be directly detected by the fire temperature sensor on the circuit breaker, then the automatic fire protection function will not be achieved. 2. Main Functions 2.1 Ordinary Switching Function: During normal power use, it allows for manual closing and opening of the controlled circuit. 2.2 Automatic Fire Protection Function: When a fire occurs at the location of the circuit breaker (or the location monitored by the sensor in the split type), and the ambient temperature rises abnormally, the temperature sensor of the circuit breaker will automatically cut off the power supply to the controlled circuit after sensing that the ambient temperature has reached or exceeded the set temperature. This prevents the fire from spreading and provides electrical safety for firefighting operations, preventing secondary injuries to firefighters from electric shock. 2.3 Overload Protection Function: When the load on the circuit controlled by the automatic fire protection circuit breaker exceeds the rated value, the circuit breaker will automatically disconnect the current to the controlled circuit in a timely manner, preventing a fire caused by overheating. 2.4 Short-circuit protection function When an accidental short circuit occurs in the circuit controlled by the automatic fire protection circuit breaker, the circuit breaker will disconnect within 0.2 s to cut off the power supply of the controlled circuit and prevent the short circuit from causing a fire. 2.5 Residual current protection function When the insulation of the controlled circuit or electrical equipment is damaged, resulting in a ground fault or a single-phase electric shock accident (Note: phase-to-phase leakage and electric shock cannot be protected), the automatic fire protection circuit breaker will automatically cut off the power supply of the controlled circuit within 0.1 s (household type) or 0.2 s (industrial type) to avoid harm to human life and prevent the possibility of electrical fire caused by such residual current. 3 Applicable places Automatic fire protection circuit breakers are classified according to their usage category, usage method, number of phases of the controlled circuit, and the controlled object and nature as follows: 3.1 Classified by usage category (1) Household and similar places: such as HNB47FL type, rated current ≤63 A, code B. (1) Suitable for residential homes, offices and similar places. (2) For industrial and similar places: such as HNM20FL type, rated current ≤630 A, code is M. Suitable for factories, shopping malls and other places with large power consumption. 3.2 According to the usage method, circuit breakers can be divided into three types: A, B and C. 3.3 According to the number of poles (1) Household type: 1P+N, 2P, 3P, 3P+N, 4P, code is directly marked as such. Used in single-phase, three-phase and three-pole four-wire circuits respectively. (2) Industrial type: 2300 (2P), 3300 (3P), 3N300 (3P+N), 4300 (4P), code is directly marked as such. Used in single-phase, three-phase and three-pole four-wire circuits respectively. 3.4 Classified by instantaneous tripping current (1) Household type: The code for lighting distribution is C before the rated current value, used for general lighting and electrical control; the code for motor protection is D before the rated current value, used for motor short circuit protection. (2) Industrial type: No special mark is added for distribution; the code for motor protection is 2 after the tripping device type and accessory code, used for motor short circuit protection. 4 Main issues to consider in design and selection The comprehensive protection function and the function of implementing electrical protection of the automatic protection function circuit breaker for electrical fire have certain conditions. Only with appropriate selection can the best effect be achieved. Therefore, when designing the circuit configuration, the following parameter configurations should be considered: 4.1 Rated current configuration When designing the rated current of the automatic protection function circuit breaker for electrical fire, it should be selected so that it does not exceed the nominal value of its rated current when the circuit is fully loaded. If the selection is too small, the circuit is very easy to enter the overload protection state, which can easily cause frequent power outages; if the selection is too large, even if the actual power load of the circuit exceeds the rated value of the circuit design by a large margin, it will not be overload protected. The function of preventing fires caused by overload will be lost. 4.2 Short-circuit current selection The protection against short-circuit current should be selected according to the nature of the load. If the load is general lighting and ordinary electrical equipment, the instantaneous tripping current should be selected as the distribution protection type. Its protection range: 5-10 In for household type, 10 In ± 20% for industrial type. For lines where the load is mainly a motor, the instantaneous tripping current should be selected as the motor protection type. Its protection value: 10-50 In for household type, 12 In ± 20% for industrial type. 4.3 Determination of the maximum allowable residual current (rated residual operating current) When the automatic electrical fire protection circuit breaker is installed at the end of the line and its main function is to protect people from electric shock, its rated residual operating current value shall not exceed 30 mA. Its residual current operating time shall not exceed 0.1 s. When an automatic electrical fire protection circuit breaker is configured in the first (two-level protection) or second (three-level protection) stage of a circuit, primarily for protecting against ground fault currents, its rated residual operating current should not exceed 500 mA. If the actual residual current in the circuit exceeds this range, an electrical fire may occur due to this leakage current. However, its rated residual non-operating current should not be less than twice the maximum leakage current of the protected electrical circuit and equipment during normal operation (abnormal leakage current values ​​should not be used as a basis for calculation). 5. Situations where Type A circuit breakers are not suitable: Type A indoor automatic electrical fire protection circuit breakers are not suitable in the following situations. (1) The installation location of the automatic fire protection circuit breaker is inside the lighting box, and the lighting box has a movable cover that covers the surface panel where the handle of the automatic fire protection circuit breaker is located, which hinders the fire monitoring probe from sensing the temperature of the monitored space; (2) When the location where a fire may occur needs to be monitored is far from the circuit breaker installation location, even if a fire occurs, the fire monitoring probe can only sense the temperature change when the fire develops to a very serious level; (3) When the monitored location is a long and winding environment. For the above situations, a type C (split-type) automatic fire protection circuit breaker must be used, and its split fire monitoring probe is extended with a wire and installed at the nearest position to the location where fire monitoring is needed. If necessary, a multi-probe circuit breaker can be ordered for multi-point monitoring, so that the circuit can be immediately tripped when a fire occurs, rather than waiting until the fire develops to a very serious level, so as to achieve the effect of early prevention and protection. 6. Conclusion GB 13955-2005, "Installation and Operation of Residual Current Operated Protective Devices," is the latest revised national standard. The standard further clarifies that residual current operated protective devices include "various circuit breakers with residual current operated protection functions, mobile residual current operated protective devices, residual current operated electrical fire monitoring systems, residual current operated relays, and their combinations, etc." Automatic circuit breakers for electrical fire protection integrate electric shock protection, electrical fire prevention, and automatic protection in the event of a fire into a single unit, meeting the higher requirements of society for electrical fire prevention. GB 13955-2005 explicitly states: "Buildings and residences of enterprises and institutions should adopt graded protection, and the residual current protection devices at the power supply end of buildings should meet the functional requirements for preventing electrical fires." For "urban power distribution networks, when adopting graded protection within power-consuming units, the use of residual current protection devices for preventing electrical fires should also be considered." Correspondingly, new fire protection standards for fire protection and residential buildings have also been revised and will be promulgated soon. This has established comprehensive system specifications for fire prevention work, covering design, installation, and operation management. Automatic circuit breakers and electrical fire monitoring systems will play a more active role in preventing electrical fires in my country, reducing the frequency of electrical fires, ensuring safe electricity use, and protecting the lives and property of the nation and its people.