1. Introduction to IEC 60228 Standard

The International Electrotechnical Commission’s IEC 60228 standard covers the nominal cross-sectional areas for conductors of insulated electric power cables and cords. This fundamental international standard specifies requirements for solid and stranded copper, aluminium, and aluminium alloy conductors in cables for fixed installations, as well as flexible copper conductors for portable equipment and flexible cords.

IEC 60228 focuses on the physical and electrical properties of conductors, including their cross-sectional area, resistance values, and the number and arrangement of strands within a conductor. This standard ensures that conductors in cables meet specific performance requirements for electrical safety and reliability across all international markets.

A key distinction of IEC 60228 is that it defines conductors by their nominal size determined by resistance rather than physical dimensions. This is critical because not all copper has the same resistivity value — a 4mm² conductor from two different suppliers may have different resistance values if specified by dimensions alone. IEC 60228 provides a standardized definition based solely on electrical characteristics.

Source: Eland Cables – IEC 60228 Standard Cable

2. Conductor Classification System

IEC 60228 classifies conductors into four classes based on their construction and intended flexibility. Each class is designed for specific application groups, and understanding these differences is essential for proper cable selection.

2.1 Class Application Summary

Important: IEC 60228 only permits the use of aluminium for Class 1 and Class 2 conductors. Flexible cables (Class 5 and 6) require copper conductors because aluminium has inferior mechanical properties for repeated bending applications.

Source: Ngoc Lan Cable – IEC 60228 Specs & Classification

3. IEC 60228 Conductor Sizes

IEC 60228 specifies nominal cross-sectional areas ranging from 0.5mm² to 2500mm² (expanded to 3000mm² in the 2023 edition). These sizes are specified in metric values — the US continues to use the American Wire Gauge (AWG) system instead.

3.1 Standard Cross-Sectional Areas

3.2 AWG to IEC 60228 Conversion

4. Maximum Resistance Values at 20°C

Each conductor size in IEC 60228 is required to meet a maximum resistance value measured at 20°C. This is the defining characteristic that ensures consistent electrical performance regardless of physical construction variations.

4.1 Class 1 & Class 2 — Fixed Installation Conductors

4.2 Class 5 & Class 6 — Flexible Conductors (Copper Only)

Note: Class 5 and 6 conductors have approximately 4-5% higher resistance than Class 1 and 2 with the same cross-sectional area. For example, a 10mm² Class 2 copper conductor has maximum resistance of 1.83 Ω/km, while Class 5 with the same area has 1.91 Ω/km.

Source: Nexans – IEC 60228 Classification Tables

5. Minimum Number of Wires

IEC 60228 specifies the minimum number of wires required for stranded conductors. Class 5 and 6 require progressively more wires with smaller diameters to achieve greater flexibility.

6. Conductor Materials

6.1 Copper Conductors

6.2 Aluminium Conductors

Source: Wikipedia – IEC 60228

7. Key Technical Parameters

8. International Standard Adoption

IEC 60228 has been adopted by CENELEC as a European standard and subsequently ratified by all member countries. It is referenced under various national designations across Europe and internationally.

Note: The US and Canada continue to use the American Wire Gauge (AWG) system and kcmil for larger sizes. IEC TC 20 cable product standards do not prescribe cables with AWG/kcmil conductors, though IEC TR 62602 provides guidance for AWG conductor specifications.

9. Application by Conductor Class

Source: Cleveland Cable Company – IEC 60228 Cable

10. Temperature Correction Factors

IEC 60228 specifies that resistance values are measured at 20°C. Annex B provides exact formulae for temperature correction factors to convert measured resistance at other temperatures to the standard 20°C reference.

Formula: R₂₀ = Rt × kt where Rt is measured resistance at temperature t°C