— A Practical Guide for Engineers, EPCs, and Project Teams
The conductor inside a cable is not just “copper.” Its internal stranding structure determines the cable’s flexibility, its resistance per unit length, its ability to withstand bending and vibration, and—ultimately—its suitability for a given installation. IEC 60228 is the international standard that classifies these conductor constructions. It defines four classes for copper conductors: Class 1 (solid), Class 2 (stranded), Class 5 (flexible), and Class 6 (highly flexible) .-2
Choosing the wrong conductor class is a common and costly error. A Class 1 conductor installed in a vibrating machine will fatigue and fracture. A Class 6 conductor specified for a fixed installation adds unnecessary cost without functional benefit. This guide explains the differences between the four classes, their electrical and mechanical characteristics, and the selection logic that engineers should apply.
1. Why IEC 60228 Matters
IEC 60228 specifies nominal cross-sectional areas (from 0.5 mm² to 2,000 mm²), numbers and diameters of wires, and maximum DC resistance values at 20°C. Crucially, the standard defines the conductor class by its stranding structure, not by its application. The class itself is a property of the conductor, and its suitability for a given installation is a separate engineering decision.-2-32
The four classes serve two fundamentally different installation regimes:
| Installation Regime | Classes | Purpose |
|---|---|---|
| Fixed installations | Class 1, Class 2 | Conductors that will not move after installation |
| Flexible applications | Class 5, Class 6 | Conductors that must withstand bending or movement |
2. Class 1: Solid Conductor
Structure: The conductor core is formed by a single, solid wire.-4
Key characteristics:
| Property | Implication |
|---|---|
| Highest rigidity | Cannot be bent repeatedly; suitable only for fixed, immovable installation |
| Lowest DC resistance for a given cross-section | A solid conductor has the lowest resistance per unit length among the four classes, because there are no air gaps or contact resistances between strands |
| Largest minimum bending radius | Requires the greatest care during installation to avoid kinking or damaging the insulation |
| Smallest diameter for a given cross-section | More compact than stranded equivalents |
Typical applications: House wiring, flush-mounted installation, switchboards, and any fixed wiring where the cable will not be moved after commissioning. Class 1 is common in smaller cross-sections (e.g., 1.5 mm², 2.5 mm²) for building installation.-4-32
Selection rule: Use Class 1 only where the cable is permanently fixed and will never be subjected to repeated bending or vibration.
3. Class 2: Stranded Conductor
Structure: The conductor is formed by multiple wires stranded together into a “cord”. The standard specifies a minimum number of wires and a maximum DC resistance at 20°C for each nominal cross-section.-4
Key characteristics:
| Property | Implication |
|---|---|
| Moderate flexibility | Can be bent during installation without damage, but is not designed for continuous flexing |
| Lower resistance than Class 5 for the same cross-section | The larger individual strands of Class 2 provide a lower resistance path than the finer strands of Class 5-4 |
| More robust than Class 1 | Resistant to the mechanical stresses of installation in conduits, trays, and trenches |
| Good for larger cross-sections | Class 2 is the standard choice for power cables in industrial fixed installations, particularly at 16 mm² and above-32 |
Typical applications: Industrial power cables, control cables, and fixed wiring in trays, conduits, and underground ducts. For large cross-sections where a solid conductor would be impractical to handle, Class 2 is the standard solution.-32
Selection rule: Use Class 2 for fixed installations that require more handling flexibility than Class 1 can provide—which covers the vast majority of industrial power and control cables.
4. Class 5: Flexible Conductor
Structure: The conductor is formed by a large number of thin wires (fine-stranded). The standard specifies a maximum diameter of the individual wires (rather than a minimum number of wires) and a maximum DC resistance at 20°C.-4
Key characteristics:
| Property | Implication |
|---|---|
| High flexibility | Suitable for cables that must be bent repeatedly or routed through tight spaces |
| Higher resistance than Class 2 for the same cross-section | The finer wires and the small air gaps between them increase the DC resistance compared to a Class 2 conductor of identical nominal area-4 |
| Smaller individual wire diameter | The maximum permissible wire diameter is smaller than for Class 2, which is what enables the increased flexibility-32 |
| Suitable for occasional movement | Class 5 is appropriate for flexible cables, cable drums, and applications involving occasional movement or re-positioning-32 |
Typical applications: Flexible cables for industrial, residential, and commercial use; cable drums; control cabinet wiring; connecting leads where occasional movement is expected.-32
Selection rule: Use Class 5 where the cable requires flexibility during installation or occasional movement in service—but not for continuous flexing in high-cycle applications.
5. Class 6: Highly Flexible (Extra-Flexible) Conductor
Structure: The conductor is formed by even more wires of a still finer diameter than Class 5. The maximum individual wire diameter is smaller than for Class 5.-4-32
Key characteristics:
| Property | Implication |
|---|---|
| Highest flexibility | Designed for continuous movement and vibration |
| Smallest individual wire diameter | Provides the greatest resistance to bending fatigue and strand breakage |
| Higher resistance than Class 5 | The even finer stranding increases resistance further relative to Class 2 and Class 5 for the same cross-section |
| Best fatigue life | The many fine strands distribute bending stress, extending service life in dynamic applications |
Typical applications: Robotics, automation, cable tracks (drag chains), welding cables, and any application involving continuous or high-frequency movement. Class 6 is also used in extra-flexible welding cables and special flexible cables with unusually short lays.-32
Selection rule: Use Class 6 only where the cable will be subjected to continuous flexing, high-cycle bending, or significant vibration. Using Class 6 in a fixed installation is over-specification.
6. Head-to-Head Comparison
| Feature | Class 1 | Class 2 | Class 5 | Class 6 |
|---|---|---|---|---|
| Structure | Solid single wire | Stranded, multiple wires | Fine-stranded, many thin wires | Extra-fine-stranded, even more and finer wires |
| Flexibility | Lowest | Moderate | High | Highest |
| Primary installation | Fixed, immovable | Fixed, immovable | Flexible / occasional movement | Continuous flexing / high vibration |
| DC resistance (same nominal area) | Lowest | Low | Higher than Class 2 | Higher than Class 5 |
| Individual wire diameter | N/A (single wire) | Larger strands | Smaller strands | Smallest strands |
| Bending fatigue resistance | Poor | Moderate | Good | Excellent |
| Typical applications | Building wiring, switchboards | Industrial power and control cables | Flexible cables, cable drums, cabinet wiring | Robotics, drag chains, welding cables |
| Cost (relative) | Lowest | Low | Moderate | Highest |
The resistance trade-off: The progression from Class 1 to Class 6 involves a trade-off between flexibility and electrical resistance. As the individual wire diameter decreases to improve flexibility, the DC resistance for a given nominal cross-section increases. This is why a Class 2 conductor and a Class 5 conductor of the same nominal area do not have identical resistance—the Class 5 conductor has a higher maximum DC resistance.-4
7. Selection Decision Guide
| If the installation requires… | Choose… | Why |
|---|---|---|
| Permanent, immovable wiring | Class 1 | Lowest cost; adequate for fixed installation |
| Fixed installation with handling during pulling | Class 2 | Robust; lower resistance; handles installation stresses |
| Occasional movement or re-positioning | Class 5 | Flexible enough for occasional bending without fatigue |
| Continuous flexing, drag chains, robotics | Class 6 | Highest fatigue resistance; designed for dynamic service |
| Lowest possible resistance for a given area | Class 1 or Class 2 | Solid or large-strand construction minimises resistance |
| Smallest possible bending radius | Class 6 | Finest stranding enables the tightest bends |
| Vibration-prone environment (fixed cable) | Class 5 or Class 6 | Stranded construction resists fatigue better than solid |
A practical warning: Do not assume that “stranded” means “flexible enough.” A Class 2 stranded conductor is suitable for fixed installation, not for continuous flexing. A Class 2 conductor installed in a drag chain will fail from strand fatigue—often within a fraction of the expected service life. The correct choice for dynamic applications is Class 5 or Class 6, depending on the severity of the movement.
8. Common Mistakes to Avoid
| Mistake | Consequence | Prevention |
|---|---|---|
| Using Class 1 in a vibrating application | Conductor fracture; open circuit | Use Class 5 or Class 6 for any movement |
| Using Class 2 in a drag chain | Strand fatigue; premature failure | Use Class 6 for continuous flexing |
| Using Class 6 for fixed wiring | Unnecessary cost; no performance benefit | Use Class 1 or Class 2 for fixed installation |
| Assuming Class 5 and Class 2 have identical resistance | Voltage drop miscalculation | Account for the higher resistance of Class 5 |
| Selecting by “stranded” alone without specifying the class | Wrong flexibility or resistance for the application | Always specify the IEC 60228 class explicitly |
| Ignoring the maximum wire diameter requirement | Non-compliant cable; unpredictable flexibility | Verify the conductor meets the class-specific wire diameter limits |
| Using a Class 1 conductor where bending during installation is unavoidable | Insulation damage; conductor kinking | Use Class 2 where handling flexibility is needed |
9. Why Choose Anhui Tiankang for Conductor-Compliant Cables?
Anhui Tiankang (Group) Co., Ltd. has nearly five decades of experience in industrial cable manufacturing. We manufacture cables with conductors fully compliant with IEC 60228, and we help EPCs select the correct conductor class for each application.
Conductor class support:
| Class | Tiankang Cable Types | Typical Applications |
|---|---|---|
| Class 1 | Building wire, small-size fixed installation cables | Switchboards, flush-mounted wiring |
| Class 2 | Power cables, control cables, armoured cables | Industrial fixed installation, trays, ducts, burial |
| Class 5 | Flexible control cables, instrumentation cables | Cabinet wiring, occasional movement, flexible connections |
| Class 6 | Drag-chain cables, robotic cables, welding cables | Continuous flexing, automation, dynamic service |
Core advantages:
Full IEC 60228 compliance: Conductors verified for wire diameter, stranding, and maximum DC resistance
Complete certifications: CCC Ex, ATEX, IECEx, SIL, CCS marine
CNAS-accredited laboratory: Full electrical and mechanical performance testing
Engineering support: Conductor class selection, voltage drop calculation, and installation guidance
One-stop supply: From cables to glands to installation accessories
10. Conclusion
IEC 60228 Class 1, 2, 5, and 6 are not arbitrary grades—they are engineering classifications that determine how a conductor behaves mechanically and electrically. The choice between them is a balance between flexibility, resistance, robustness, and cost.
Key takeaways:
| Class | Structure | Flexibility | Resistance | Best For |
|---|---|---|---|---|
| 1 | Solid wire | Lowest | Lowest | Fixed, immovable wiring |
| 2 | Stranded | Moderate | Low | Fixed installation with handling |
| 5 | Fine-stranded | High | Higher than Class 2 | Flexible / occasional movement |
| 6 | Extra-fine-stranded | Highest | Highest | Continuous flexing, vibration |
The most important rule: Specify the conductor class explicitly. “Stranded” is not a specification—Class 2, Class 5, and Class 6 are all stranded, but they serve fundamentally different purposes. The wrong class will either fail prematurely (too rigid for movement) or waste money (too flexible for a fixed installation).
Remember: The conductor is the part of the cable that carries both the current and the mechanical stress. Selecting the correct IEC 60228 class is not a detail—it is the foundation of cable reliability.
Contact Us
For cable selection with the correct IEC 60228 conductor class, technical documentation, or project quotations, please contact:
Yin Shuangjie
International Sales Manager
📧 Email: [email protected]
📱 WhatsApp / Zalo: +86 17856068126
🌐 Website: http://www.tiankang-global.com/
Anhui Tiankang – Your partner for reliable industrial cable solutions.
