Cable specifications often include terms such as “Class 2 copper conductor” or “Class 5 flexible copper conductor.” What do these classes mean, and does a higher number indicate better copper?
Understanding conductor classes helps buyers read technical specifications, communicate requirements and select cables for their intended applications.
What Does Conductor Class Mean?
IEC 60228, Conductors of insulated cables, defines four conductor classes: Class 1, Class 2, Class 5 and Class 6. These distinguish solid, stranded and flexible conductor constructions. The standard also specifies relevant construction and resistance requirements.
A conductor class is not a copper purity grade. “Class 5” does not mean that the conductor contains five wires.
Source: IEC 60228:2023.
The Four Conductor Classes
| Class | Construction | General application |
|---|---|---|
| Class 1 | Solid conductor | Fixed installations |
| Class 2 | Stranded conductor | Fixed installations |
| Class 5 | Flexible copper conductor made from fine wires | Flexible cables and cords; also permitted for fixed installations |
| Class 6 | Flexible copper conductor using smaller-diameter wires than Class 5 at the same nominal cross-sectional area | Products requiring greater conductor flexibility |
“Solid” and “stranded” describe the construction within an individual conductor, not the number of cores in a cable.
Source: IEC 60228:2023, Clause 4.
Why Do Fine Wires Improve Flexibility?
A thin wire bends more easily than a thick wire. Building a conductor from many fine wires therefore helps create a flexible construction.
However, conductor construction is only part of the picture. Insulation, sheathing, shielding and the arrangement of components also affect how the finished cable bends.
Always check the cable’s specified minimum bending radius. Product data sheets may give different limits for fixed installation and flexible use, even for the same cable.
Example: HELUKABEL Class 5 control cable data sheet.
What About Class 3 and Class 4?
The current IEC 60228 classification does not include Class 3 or Class 4. Its numbering is not a continuous scale from 1 to 6.
IEC’s historical description of the 1966 edition states that the number of conductor classes was reduced from six to four, listing Classes 1, 2, 5 and 6.
Source: IEC 60228:1966.
If a specification mentions Class 3 or Class 4, check the referenced standard and its edition before interpreting the term.
Other electrical classification systems use similar names for different purposes. For example, North American Class 3 circuits and Class 4 fault-managed power systems concern circuit and power-system classifications—not the flexibility of an IEC copper conductor.
Source: Belden: Differences Between Circuit Classes.
Does a Higher Class Mean a Better Cable?
Conductor class is not an overall cable quality rating. The appropriate construction depends on the application.
A cable installed in a fixed position has different requirements from one that moves repeatedly in machinery. Being easy to bend during installation does not, by itself, establish suitability for continuous flexing.
For cable-chain or repeated-motion applications, check the finished cable’s intended use, bending radius, operating conditions and relevant test data. Class 5 or Class 6 alone does not establish its service life in motion.
Further reading: HELUKABEL: Flexible Cables for Motion Applications.
Does Class 5 Mean Tinned Copper?
No. Class 5 conductors are available in both plain copper and tinned copper constructions. The conductor class and the surface coating are separate specification details.
For example, HELUKABEL lists both plain copper Class 5 conductors and tinned copper Class 5 conductors.
How to Specify Your Requirements
Instead of requesting only “flexible copper wire,” provide a more precise conductor description, such as:
“2.5 mm² nominal cross-sectional area, Class 5 plain annealed copper conductor conforming to IEC 60228.”
This describes the conductor only. A complete cable enquiry should also state the number of cores, rated voltage, insulation and sheath materials, applicable cable standard, and installation or movement conditions.
By specifying conductor class alongside these requirements, buyers and suppliers can communicate more accurately and assess whether a cable suits the intended application.
