Published: 2025-08-08 10:37:53
To prevent fires caused by cable current overload, it is necessary to take systematic measures throughout the entire process, including design, selection, installation, and operation and maintenance, in combination with technical specifications and management requirements, to eliminate overload hazards. The following are specific prevention and control points:
1. Design phase: Avoiding the possibility of overload from the source
Accurately calculate the current carrying capacity and select the model reasonably
Based on the total power of the electrical equipment, operating current (including starting current, peak current), and the cable installation environment (such as temperature, heat dissipation conditions, whether conduit is inserted or buried), the required current-carrying capacity for cables is calculated strictly according to standards such as the "Code for Design of Low-Voltage Distribution"GB50054 and select cables with sufficient cross-sectional area (the larger the conductor's cross-sectional area, the greater the current-carrying capacity).
Avoid 'a small horse pulling a big cart': for example, a 10kW three-phase motor has a rated current of about 20A, so a 4mm² or larger copper cable should be selected (the current-carrying capacity for exposed installation is about 30A), rather than 2.5mm² (current-carrying capacity about 25A, insufficient margin).
Branch circuit design to avoid concentrated overloading
Set up separate circuits for high-power equipment (such as air conditioners and electric welders) to avoid multiple devices sharing the same cable; wiring for lighting, sockets, and other circuits should be separated to reduce the load pressure on a single circuit.
The cable between the main distribution box and the sub-distribution box should reserve 10%-20% of load margin to accommodate possible future load growth.
2. Installation Phase: Ensure Safe Operating Conditions for Cables
Standardized installation to ensure heat dissipation
Avoid excessive bending, squeezing, or stacking when laying cables, and ensure good heat dissipation: when laying cables through conduits, the total cross-sectional area of cables inside the conduit should not exceed 40% of the conduit’s cross-sectional area; the spacing between cables in a cable tray should not be less than 1.5 times the cable diameter to avoid being "airtight".
Away from heat sources (such as boilers and radiators), in high-temperature environments, high-temperature resistant cables (such as cross-linked polyethylene insulated cables) should be selected, or insulation measures should be taken.
Eliminate illegal connections and damage
Cable joints are weak points. Improper handling of joints can lead to increased contact resistance, causing local overheating and triggering overloads (a vicious cycle). They need to be handled by professionals using standard processes such as crimping or fusion, and sealed with insulated waterproof sleeves.
Before laying, check whether the cable insulation is damaged. Damaged cables are strictly prohibited from use; when threading through a conduit, avoid being scratched by the sharp edges of the conduit opening.
3. Operation phase: Real-time monitoring and load management
Install overload protection device
Install circuit breakers (air switches) or fuses in the distribution circuit, and their rated current should be less than the maximum current carrying capacity of the cable (for example, a 4mm² cable matched with a 25A circuit breaker). It will automatically trip and cut off the power when the current is overloaded.
For important circuits (such as fire protection and industrial equipment), circuit breakers with thermal-magnetic trip functions can be installed, which can respond to overloads and also protect against short-circuit faults.
Regularly Monitor Load and Temperature
Use a clamp ammeter to regularly measure the actual operating current of cables to ensure it does not exceed the rated current; focus monitoring during high-load periods (such as peak electricity use in summer).
Use an infrared thermometer to detect the temperature of the cable surface and joints. If a localized temperature rise is found (exceeding the ambient temperature by more than 10°C), promptly investigate the cause (such as poor contact or overload).
Prohibit Unauthorized Connections and Overloading
It is strictly forbidden to independently add electrical devices to existing cables (such as "multi-outlet" extensions), especially high-power equipment (such as heaters or induction cookers).
Industrial sites need to establish load management systems to avoid simultaneous startup of multiple devices causing instantaneous overload (staggered startup can be used).
IV. Maintenance and Emergencies: Promptly Eliminate Hazards
Regular Insulation Testing and Aging Assessment
Conduct insulation resistance testing of cables every year (using a megohmmeter). If the insulation value is below the standard (for example, below 0.5MΩ for low-voltage cables), the cable must be replaced to prevent insulation breakdown causing short circuits and overloads.
For old cables over 15 years of service, evaluate if early replacement is needed based on appearance (such as cracked or hardened insulation) and operational status.
Develop Emergency Plans
Equip fire extinguishers (such as dry powder or carbon dioxide extinguishers) and regularly check the effectiveness of fire-fighting facilities.
If the cable is found to be overheating, smoking, or emitting an unusual odor, immediately cut off the power supply. Do not extinguish it with water directly (to prevent electric shock). After it has cooled down, troubleshoot the fault.
Summary
The core logic of preventing cable overload fires is: 'design with margin, install according to standards, control the load during operation, and maintain regular monitoring.' Through full-process management, the operating current of the cables is strictly limited within a safe range, while simultaneously enhancing the ability to respond to sudden overloads, fundamentally eliminating the risk of fire.