Cable Conductor Classes and Stranding Explained

What IEC 60228 Covers

IEC 60228 defines conductor requirements for insulated cables, including nominal cross-sectional areas, conductor constructions and maximum resistance values. It covers solid and stranded copper, aluminium and aluminium-alloy conductors for fixed installations, as well as flexible copper conductors. The applicable product standard still determines where a conductor construction may be used.

The current edition of the governing standard and the cable product standard should be stated in the purchase specification. A conductor should not be accepted only because its outside diameter resembles another cable.

Class 1: Solid Conductors

A Class 1 conductor is solid. It has a simple construction and is normally associated with smaller fixed-installation conductors. It is not intended for repeated flexing. Installation handling, terminal compatibility and local code requirements should be checked before selection.

Class 2: Stranded Conductors for Fixed Installation

Class 2 conductors use multiple strands and are common in fixed power cables. Circular, compacted circular and shaped conductors may be used depending on size and cable design. Compaction can reduce conductor diameter and overall cable size, but it also changes the way strands appear at a cut end.

Do not judge a compacted conductor as underfilled from appearance alone. Verify the ordered construction, conductor resistance and relevant dimensional requirements.

Class 5 and Class 6: Flexible Conductors

Class 5 uses finer strands for flexible cables and wires. Class 6 uses still finer construction for applications requiring greater flexibility. The class describes the conductor, not the complete cable's suitability for continuous movement. Insulation, sheath, lay length, reinforcement and bend design also control flex life.

A highly flexible conductor can be the wrong choice for a fixed power feeder if the terminal is designed for a different conductor type. Flexible strands may require ferrules, lugs or terminals specifically approved for that construction.

Why Strand Count Alone Is Misleading

Buyers sometimes compare cables only by strand count. That can be misleading because strand diameter, compaction, conductor material and class all matter. Unless a product standard or drawing specifies strand count, conductor resistance and class are usually more meaningful acceptance controls.

Tinned copper may be specified for corrosion resistance or termination needs, but tinning does not replace a suitable sheath or environmental design. Aluminium conductors require compatible connectors, joint preparation and installation practice.

Conductor Resistance and Temperature Correction

DC resistance is commonly measured and corrected to a reference temperature, often 20 degrees C under the applicable standard. The measured sample length, conductor temperature, instrument accuracy and connection method affect the result. A factory or third-party report should identify these conditions rather than show only a final number.

Resistance that is too high may indicate insufficient conductive material, incorrect material, poor joints or measurement error. Passing resistance does not by itself prove insulation thickness, voltage rating, fire performance or service suitability.

Termination and Installation Questions

• Will the cable be fixed, occasionally moved or continuously flexed?
• What terminal, lug or connector will receive the conductor?
• Does the terminal accept compacted, sector-shaped or fine-stranded conductors?
• Is vibration present?
• What minimum bending radius applies to the finished cable?
• Are ferrules, special lugs or crimp tools required?