For fire power equipment, such as fire pumps, smoke prevention fans, fire elevator distribution lines and other power supply circuits that cause greater losses due to power outages caused by overload, how should they be implemented? The relevant specifications are detailed as follows: "General Code for Building Electrical and Intelligent" GB 55024-2022, Article 43.1. For the power supply circuit that causes greater losses due to power failure caused by overload, the overload protection should act on the signal alarm and should not cut off the power supply.
Code for Electrical Design of Civil Buildings GB 51348-2019, No. 76.3. For lines where the loss caused by sudden power failure is greater than that caused by overload, overload protection should not be set. (Repealed).
Code for Design of Low-Voltage Power Distribution GB 50054-2011, No. 63.6 lines, overload power failure will cause serious consequences, its overload protection should not cut off the line, can act on the signal.
Specifically, it is implemented according to the following principles:1.The circuit breaker in the control box (cabinet) of fire-fighting equipment is not provided with long-delay overload protection. For the fire pump that is used and standby, the working pump is overloaded, and the thermal relay is alarmed, and the main circuit contactor is cut off at the same time, and the standby pump is started, the standby pump is overloaded, and the thermal relay only alarms and does not act;
For fire-fighting equipment such as smoke exhaust fans used only for fire-fighting or single-speed fans for fire-fighting and usual use, the thermal relay of the fire-fighting equipment control box (inside) only alarms and does not act;
For the two-speed fan that is used both for fire fighting and usual, the thermal relay in the low-speed (usual) control loop cuts off the main loop contactor and alarms when it acts, and the thermal relay in the high-speed (fire-fighting) control loop only alarms and does not act.
1) The circuit breaker adopts an electromagnetic tripper, or an electronic tripper is used to cancel the overload function. (2) When an overload occurs during operation, the thermal relay sends a signal to act on sound and light (the alarm or indicator light on the distribution box or to monitor the background of the system) to display the alarm function, instead of tripping the contactor.
When the fire-fighting equipment group (i.e., multiple fire-fighting equipment) connected to the distribution trunk is only used in the fire-fighting state, the protection appliances at all levels are required to set up long-delay protection (to avoid the maximum overload current). The fire power supply circuit should use a circuit breaker that only alarms and does not trip when overloaded. 
The calculation method of the maximum overload current that may occur when avoiding the fire fighting state is as follows: (1) The power distribution trunk of the fire pump is calculated according to the rated current of 3 times the maximum power motor during fire fighting plus the normal calculation current of other simultaneous operating loads;
2) The fire fan distribution trunk line is 2 of the maximum power motors of 1 2 sets when fire fighting5 times the rated current plus the normal calculated current for other simultaneous operating loads; (3) The power distribution trunk of fire-fighting equipment such as fire-fighting elevators, fire-fighting emergency lighting, and automatic fire alarm systems shall not be less than 1 of the normal calculated current of the circuit25 times;
4) When the distribution trunk includes the above two situations, take the maximum value in each case.
In addition, the relationship between the current carrying capacity of the fire line conductor and the long delay setting value of the distribution trunk circuit breaker is not considered, but the current carrying capacity of the conductor should not be less than 1 of the normal calculated current of the line25 times, and the effect of the ambient temperature of the fire on the increase in voltage drop should be considered.
The non-tripping device of thermal overload alarm non-tripping circuit breaker comprises three groups of tripping mechanisms that contain bimetallic sheet, support, drawbar tripping mechanism and the rotating shaft that runs through three groups of tripping mechanisms, a bracket is arranged on the bimetal sheet in each group of tripping mechanism, described rotating shaft passes through the drawbar, the stress direction of the drawbar points to the axis of the rotating shaft, each group of tripping mechanism also comprises a micro switch and a thermal element, the micro switch is fixed on the bimetal sheet through the support, the micro switch is also connected with the peripheral alarm circuit, and the thermal element is connected with the bimetal sheet. The micro switch is installed on the bimetal sheet as a trigger device, providing normally open contacts for the peripheral alarm circuit, and realizing the overload alarm non-tripping function of the thermomagnetic molded case circuit breaker, which has a simple structure, low cost, can continue to work reliably in a high temperature environment, and has the alarm characteristics of overload and long delay action, which can meet the requirements of continuous power supply in special places such as fire protection, chemical industry and medical treatment. 