When a cable overheats, it is essentially due to excessive current in the conductor, poor contact, poor heat dissipation, and aging insulation, etc. If the temperature exceeds the allowable working temperature of the cable, it will trigger a series of progressively worsening faults, ranging from performance degradation to fire.
1. Accelerated insulation aging and significantly shortened lifespan
The insulation layer of the cable (PVC, cross-linked polyethylene XLPE, etc.) is highly sensitive to temperature.
If the temperature exceeds the limit for a long time, the insulation material will undergo thermal aging: hardening, becoming brittle, cracking, and losing elasticity.
With each increase in temperature by a certain range, the insulation lifespan will decrease exponentially. A cable that could originally last for 20-30 years may fail after only a few years.
Micro cracks form in the insulation, allowing moisture to invade, further deteriorating the insulation performance.
2. Insulation breakdown, resulting in leakage and short circuits
After the insulation ages and becomes thinner, or develops cracks, its insulation withstand voltage capacity decreases.
Leakage: The insulation resistance decreases, causing the casing to become electrified, creating a safety hazard of electric shock, and the leakage protector frequently trips.
Phase-to-phase short circuits / Ground short circuits: The insulation is completely damaged, with direct short circuits between phase lines or between phase lines and the ground, generating a huge short-circuit current and burning the equipment.
3. Damage to connectors and terminals, amplifying contact faults
The connectors and terminal blocks of the cable are weak heat dissipation points. Overheating will lead to a vicious cycle:
The metal terminals oxidize and become loose, causing the contact resistance to further increase, resulting in more severe heating.
There will be sparking, arcs, and the connection terminals will be burned, causing the circuit to suddenly lose power.
4. Fire and combustion, electrical fires (the most serious consequence)
The insulation layer of the cable becomes soft and melts due to high temperature, subsequently igniting the insulation sheath; PVC cables will also release a large amount of toxic smoke when heated.
Arcs and high temperatures ignite the surrounding cables and combustibles, which are important causes of electrical fires.
Many cable fires occur early on, with no obvious faults, and then suddenly burst into flames.
5. Degradation of conductor performance, increased line loss
As the conductor temperature rises, the resistance increases, the line voltage drop increases, and the terminal voltage becomes lower.
The power loss increases, wasting electrical energy; the load equipment may malfunction due to insufficient voltage.
6. Chain damage to adjacent equipment
Cable overheating will bake adjacent cables, causing the entire bundle of cables to age collectively;
Short-circuit faults will impact power distribution cabinets, switches, frequency converters and other electrical equipment, causing equipment to burn out.
Common causes of cable overheating
- The selected cable cross-section is too small, causing overload operation
- Poor crimping of the connectors, loose terminals
- Dense cable laying and blocked conduits, poor heat dissipation conditions
- The insulation has aged and is operating with faults
- Harmonic currents cause the cable to heat up
Simple judgment of signals
If the cable outer skin is abnormally hot, hard, discolored, or has a burnt smell, it is an overheating warning. You must immediately investigate and do not continue to operate under load.
