Full analysis of the hidden dangers of overheating of wires and cables: 6 core causes and scientific prevention plans
Behind a hot wire, there is a fire hazard that may be overlooked.
In modern society, wires and cables are like the blood vessels and nerves of a city, carrying the key tasks of power transmission and data circulation. With the surge in electricity demand, the problem of overheating of cables has become increasingly prominent, becoming an invisible killer threatening power safety.
According to research data, when the cable temperature exceeds the allowable value by 8°C, its service life will be reduced by more than half, and when the insulation layer temperature reaches the critical point, the risk of short circuit will increase by 300%. Behind these amazing data are countless fire accidents and equipment losses caused by overheating of cables.
Conductor resistance exceeds the standard and improper selection
The root cause of heating of wires and cables often starts from the conductor itself. When the conductor resistance exceeds the standard requirements, the ohmic loss generated when the current passes through will increase significantly, resulting in abnormal heating.
In actual applications, it is common for some projects to select cables with too small a cross-section to reduce costs, resulting in long-term overload operation of the conductor. For example, if an air conditioning line that should have used a 4mm² cross-section uses a 2.5mm² cable instead, the conductor temperature will be 15-20℃ higher than the safety threshold during continuous operation.
The conductor material is also critical. The resistivity of a conductor with recycled copper or excessive impurities may be 30% higher than that of electrolytic copper, becoming a hidden source of heat.
Scientific selection requires comprehensive consideration of load characteristics and laying environment. In industrial projects, the IEC 60287 standard should be strictly implemented to calculate the current carrying capacity, and civil places should refer to the National Electrical Code (NEC) to select matching conductor cross-sections.
For high-power equipment (≥5kW), it is recommended that the copper conductor cross-section should not be less than 4mm², and a 20% capacity margin should be reserved.
Hidden dangers of poor contact of connectors
The most vulnerable link in the cable line is often the connector. Incomplete crimping or surface oxidation will cause the contact resistance to increase exponentially, forming a local hot spot. Experimental data show that when the contact resistance reaches 1.5 times the normal value, the connector temperature can soar to more than 150℃ within 1 hour.
An investigation of a power outage in a factory showed that a cable joint with an untightened bolt in the distribution cabinet generated high temperature due to excessive contact resistance, which eventually caused a phase-to-phase short circuit and caused the entire factory to shut down for 8 hours.
To prevent such problems, it is necessary to use hydraulic crimping technology to ensure that metal molecules fully penetrate and fuse, and it is recommended to use silver plating technology for high-voltage joints to reduce the risk of oxidation.
In daily maintenance, infrared thermal imagers should be used to detect the joint temperature every quarter, and when the temperature difference exceeds the ambient temperature by 40℃, it must be handled immediately.
Installation density and environmental heat source
The heat dissipation capacity of the cable is directly related to the operating temperature. When multiple cables are densely laid, the superposition effect of heat can increase the temperature in the central area by more than 40% compared to a single cable.
A commercial building once had a cable filling rate of 85% in the bridge, resulting in a cable surface temperature of 75℃ during summer operation, far exceeding the safety limit of 60℃ for PVC insulated cables.
The specification requires that the filling rate of the cable bridge should be controlled within 40%, and layered brackets should be installed to ensure spacing when laying multiple layers.
At the same time, the influence of external heat sources must be avoided. When the cable is laid parallel to the steam pipe, the minimum spacing should be ≥1m; when it is laid crosswise, it should be ≥0.5m, and a heat insulation board should be installed. In special environments such as high-temperature workshops, high-temperature resistant cross-linked polyethylene (XLPE) insulated cables should be selected, and their long-term allowable operating temperature can reach 90°C.
Insulation aging and sheath damage
The integrity of the insulation system is the guarantee of safe operation of the cable. When the insulation resistance decreases due to aging or damage, the leakage current increases and generates dielectric loss and heat.
In particular, if the sheath of the armored cable is damaged and water enters, the water will form a water tree under the action of the electric field, causing the cross-linked polyethylene insulation performance to deteriorate rapidly. Data show that after the cable with a damaged sheath is operated in a humid environment for 6 months, its insulation resistance value may drop to 10% of the initial value.
To prevent such problems, a regular insulation test system should be established. Use a 2500V megohmmeter to test the insulation resistance every six months. For old lines that have been in operation for more than 10 years, the detection cycle should be shortened to 3 months.
The cable must be replaced when the detection value is lower than 1MΩ/km. For the direct buried section that is susceptible to mechanical damage, corrugated steel pipes should be used for protection, and warning tapes should be laid during backfilling.
Current overload and voltage overload
Abnormal fluctuations in electrical parameters are an important cause of cable overheating. When the load current exceeds the rated current carrying capacity of the cable, the heat generated by the conductor increases in a square relationship – a 10% increase in current will increase the heat generation by 21%.
Even more hidden is the voltage overload problem. When the operating voltage exceeds the rated value by 15%, the heat generated by the insulation medium loss can increase by 50%, accelerating the insulation aging process.
The intelligent monitoring system can effectively prevent such risks. By installing online temperature measurement and current monitoring devices in the distribution cabinet, cable operation data can be collected in real time.
After applying the Internet of Things technology to a substation project, 3 current mutations caused by equipment failures were successfully warned, avoiding cable overheating accidents. At the same time, a graded alarm threshold should be set: when the load reaches 90% of the rated value, an early warning is issued, and when it reaches 105%, the automatic load shedding program is started.
Design defects of cooling system
The design defects of cooling in specific environments are often overlooked. When the cable passes through the insulation layer, the heat cannot be dissipated in time, which will cause a significant decrease in current carrying capacity. Studies have shown that the current carrying capacity of 2.5mm² PVC cable in a 500mm thick insulation layer needs to be reduced by 20% to ensure safe operation.
The heat dissipation of closed channels requires special design. The cable tunnel should be equipped with a mechanical ventilation system, which automatically starts the fan to cool down when the temperature exceeds 40℃.
For underground trenches, the ventilation holes must be kept unobstructed, with a spacing of no more than 50 meters, and blockages must be cleaned regularly. In dense places such as data centers, liquid cooling cable technology can be used to remove heat through circulating coolant in the pipe, which can increase the current carrying capacity by 30% compared with air cooling.
Preventing cable overheating accidents requires the comprehensive application of technical means and management strategies. Regular inspection and intelligent monitoring are combined, and scientific selection and standardized installation are given equal importance.
The best safety solution starts with cable selection and design, runs through the entire installation and maintenance process, and ends with scientific monitoring and management. When every cable operates at a safe temperature, the modern power system can truly become a solid foundation for social development.