Do not only consider the eligible current : the hidden impact of cable diameter on heat dissipation and safety
Introduction
Some time ago, my phone's original charging cable broke. I bought a replacement, much cheaper, on the Internet. As soon as I received it, I noticed that it was lighter and thinner than the original cable. Yet, the packaging indicated the same power : « compatible 67W » et « 6A ». At first, I didn't pay attention to it. But playing on my phone while charging it, I felt the heat at my fingertips. Can this thinner cable really handle the same current safely? ?
If a simple charging cable can already present a risk of overheating because of its reduced diameter, the problem is even more critical for industrial electrical cables. In the field of electrical installations, it is not uncommon to find that two cables of the same model, displaying an identical admissible current, yet have visibly different cable diameters.
Many engineers and buyers focus only on current capacity when choosing a cable. They neglect an equally important parameter : the diameter. Or, the diameter of the cable is not a simple question of thickness. It reflects a set of factors – conductor material, manufacturing processes, type of insulation and sheath – which directly influence the heat dissipation and safety of electrical cables.
Choosing an electrical cable, it's never comparing a single number. It's finding a balance between performance, safety and overall cost. In this article, we will analyze the causes of the differences in diameter, explain their impact on cable reliability and offer a practical guide to safer and more efficient electrical cable selection.
Where do the differences in cable diameter come from? ?
Faced with two cables of the same model and the same admissible current, but having different cable diameters, many buyers feel lost. This variation is not linked to a single factor. It results from the combination of the driver, insulation and sheath materials, as well as the margin tolerated by the standards. Understanding these causes is the first step to making a reliable choice.
2.1 Driver : materials and processes
Conductor material
The conductor is the direct carrier of the electric current. Its quality determines the overall performance of the cable.
Copper without oxygen (OFC) high purity provides exceptional conductivity. It is the preferred choice for high-end cables.
Recycled copper or aluminum clad copper (CCA), although less expensive, have lower conductivity. Equal section, their electrical performance is reduced. To compensate, some low-cost cables artificially increase the overall diameter, without actually improving the current capacity.
Compaction process
With identical nominal section, a compacted conductor is denser, with less vacuum, which allows the total diameter to be reduced without losing performance. Conversely, an uncompacted conductor appears more “inflated”.
Normal compaction, in round or sectoral shape, is a beneficial process and consistent with good practice.
But some manufacturers go too far : they excessively compact the conductor to reduce sheath consumption and artificially thicken the insulation. This approach can harm the long-term flexibility and reliability of the cable.
2.2 Sheath thickness : insulation and sheathing material
Improvement of materials
Quality insulators, like the cross-linked polyethylene (XLPE), make it possible to reduce the thickness while guaranteeing the same thermal and dielectric strength. Result : a smaller total diameter without compromising safety.
Structural requirements
Adding shielding, of armor or filling materials necessarily increases the diameter. In some cases, to reinforce mechanical resistance or protection against the environment, manufacturers thicken the outer jacket, which significantly widens the cable.
2.3 The margin of standards
Whether it is Chinese standards (GB), of the IEC standard, or even UL and CE certifications, technical texts only set minimum and maximum diameter limits. They do not define a single value.
This tolerance gives manufacturers a certain freedom : they can optimize the design to reduce the diameter, or on the contrary add more sheath to reduce costs, while remaining legal.
In summary, differences in cable diameter can reveal deviations in conductor purity, variations in manufacturing processes, the quality of the insulation and sheath, as well as how each manufacturer interprets and applies standards tolerances. Understanding these elements is the first step to correctly evaluating the heat dissipation and safety of an electrical cable.
How does cable diameter influence heat dissipation and safety ?
When a cable is in service, the passage of current in the conductor generates heat by the Joule effect (I²R). If this heat is not properly evacuated, it accumulates inside the cable, causing premature aging of the insulation, overheating of the driver and, in extreme cases, a short circuit or even a fire. This is why the heat dissipation capacity and safety of an electric cable do not depend solely on the admissible current, but also differences in cable diameter.
On the physical level, heat dissipation in a cable relies on three main mechanisms :
- Conduction : heat travels from the conductor to the insulation and sheath.
- Convection : heat is transferred to the surrounding air via the surface of the cable.
- Radiation : a high temperature cable radiates heat to its surroundings.
In these three mechanisms, several factors play a determining role : the outer surface of the cable, the thickness of the insulation and the amount of heat produced by the conductor. Or, all these parameters are directly linked to the diameter of the cable.
Comparison of the causes and impacts of cable diameter differences
| Larger diameter (thicker conductor) | Larger diameter (thicker insulation/jacket or more filler) | Smaller diameter (thinner conductor) | |
| Allowable current and resistance | Increased current capacity, reduced resistance, limited losses and heating | No real improvement in admissible current or resistance | Reduced current capacity, higher resistance, risk of overheating |
| Heat dissipation | Advantages and disadvantages : less heat produced by the conductor but longer dissipation path | Impeded dissipation, heat accumulated more easily | Conductor produces more heat ; if the insulation is thin, dissipation becomes critical |
| Mechanical resistance | More resistant to wear and crushing | If thickened sheath or armor, good mechanical resistance | Less robust, requires additional protection |
| Flexibility | More rigid, reduced flexibility | More rigid, reduced flexibility | More flexible, increased flexibility |
| Ease of installation | Takes up more space, more difficult pose | Takes up more space, more difficult pose | Less bulky, easy installation and curvature |
| Cost | Higher raw material cost | Potentially higher cost (no more sheath/fill) | Lower raw material cost |
| Security risks | Lack of space, insufficient bend radius, risk of bad contacts | Reduced heat dissipation, increased long-term risk | Faster overheating, premature aging of insulation, high risk of breakdown |
In-depth security risk analysis
Risk of overheating (smaller diameter, reduced driver)
Thinner conductor means higher electrical resistance. The cable therefore heats up more easily.
Prolonged high temperature accelerates the aging of insulation, reduces cable life and may, in serious cases, cause a short circuit or fire.
Risks related to installation and connection (larger diameter)
Too large a diameter cable, installed in a restricted space, may have an insufficient radius of curvature and suffer mechanical deformation.
What's more, if the connection terminals are not suitable, the risk of bad contacts increases, which creates additional danger.
Cables swollen by too thick sheath
Some manufacturers, to give the illusion of more robust cable, add excessive sheathing or filler materials.
This increase in diameter does not improve the current capacity of the conductor in any way.. On the contrary, it hinders heat dissipation, results in higher operating temperature and creates long-term risk.
Differences in cable diameter are therefore not simple variations in thickness. They often reveal the quality of the driver, the performance of the insulation and even the overall level of security. Engineers and buyers should analyze the impact of these differences on heat dissipation and cable safety, rather than relying solely on appearance — whether a cable is “thin” or “thick”.
How to choose a truly reliable electrical cable ?
For purchasing engineers, project decision-makers and international trade professionals, selecting the right cable is not a simple task. Here are some practical steps to avoid pitfalls and ensure quality.
First step : clearly define your real needs before the call for tenders
Before sending a price request to a supplier, it is essential to establish a precise list of your needs. This helps avoid being attracted only by a low price and falling into the trap of “all admissible currents”.
Check essential electrical parameters : do not limit yourself to the admissible current. Also set the operating voltage, the short circuit capacity of the system and other key criteria.
Consider the installation environment : will the cable be laid alone or in a bundle ? What is the maximum ambient temperature ? Are there mechanical risks, chemical or flexibility needs (mobile cable) ? These elements determine whether you should choose a fire-resistant cable, armed, oil resistant or very flexible.
Evaluate the cost over the entire life cycle : the initial purchase price is just the tip of the iceberg. And quality cable, with lower resistance, reduces energy consumption. Its reliability limits production stoppages and reduces maintenance costs. This is where its true value lies.
Second step : technical survey — asking the right questions to guide the dialogue
When requesting a price, don't just ask "How much does the Model XX cable cost?" ? ». Technical questions must be asked to push the discussion deeper and, in doing so, sort suppliers.
Questions to include in your supplier survey sheet
Regarding the driver
“Is the conductor made of high purity deoxygenated copper (OFC) or recycled copper ? Can you provide conductor resistivity test report ? » (Essential : check the intrinsic quality of the conductor.)
Regarding insulation
“What is the insulation material (PVC, XLPE or other) ? What is the permitted continuous service temperature? (For example 70 °C, 90 °C or 105 °C) ? »
(Essential : evaluate the thermal class of the insulation and whether the manufacturer compensates for a conductor weakness by increasing the temperature resistance.)
Concerning the structure and the process
“Are the insulation and sheath thicknesses controlled towards the middle limit or the lower limit of the normative tolerances? ? Is the conductor compacted (compaction/tight twisting process) ? »
(Essential : know whether the manufacturer favors performance margin or cost optimization.)
Regarding application data
“In addition to the values under standard conditions, can you provide the allowable current reduction coefficient tables for real conditions (conduit installation, bundle installation, buried pose, etc.) ? »
(Essential : the ability to provide this data demonstrates technical competence and veracity of performance.)
Third step : factory audit and sample checking
For major projects or long-term partnerships, on-site audit and sample control remain the most reliable steps.
Points of attention during factory audit
Receipt of raw materials : control of quality certificates (par ex. material certificates for copper bars/cables).
Production process : observe critical operations — conductor twisting, extrusion de l’isolation, compaction, thickness control.
Online checks : check the presence of continuous monitoring equipment (online diameter sensor, spark test to detect insulation defects, automated test benches) guaranteeing consistency of quality.
Sample analysis
“Debone” the sample : cut a sample piece, peel the insulation to examine the conductor for shine and compaction, measure the actual thickness of the insulation and sheathing and compare to specifications.
Third-party testing : send the sample to an accredited laboratory for measuring the DC resistance of the conductor (resistance per km or per unit of length). DC resistance is the golden criterion for checking whether the section and quality of the conductor are compliant — the lower the measured value is than the normative limit, the better it is.
In brief
A scientific selection process moves from passive receipt of information to active investigation and verification. When you start asking about the type of insulation, the reduction coefficients in real conditions and the resistivity of the conductor, you stop being a simple price comparator to become an informed decision-maker. This helps avoid major technical and commercial risks and build the solidity and safety of your electrical installations over the long term..
Conclusion
Choosing a cable is not just about comparing prices. The main thing is in the details. Does the insulation meet standards? ? Is the sheath thickness real? ? Can the supplier provide transparent data and reliable test reports? ? These are the points that determine the safety and stability of your installations in the long term..
At ZMS Cable, we have always chosen authentic material and controlled quality. Our cables strictly comply with international IEC standards, NF and EN. During production, we apply rigorous control over the thickness of the insulation, the purity of the conductor and the composition of the sheath.
We provide our customers with complete technical data sheets, third-party testing reports and custom solutions tailored to each project, in order to protect them against the “low price” trap and guarantee them durable cables, reliable and long life.
If you are looking for a reliable and long-term cable partner, ZMS Cable is a choice that deserves your full attention.