Bs En/iec 60228 Here

0.5 – 0.75 – 1 – 1.5 – 2.5 – 4 – 6 – 10

: It details the requirements for the overall construction of the cable, including the arrangement of conductors, insulation, and any sheathing or armoring. bs en/iec 60228

Crucially, the standard defines the conductor by its maximum DC resistance at 20°C. This is a performance-based specification. Two conductors may have slightly different physical diameters due to air gaps between strands or manufacturing variances, but if they meet the resistance criteria, they are considered equivalent. This allows manufacturers some latitude in design while strictly adhering to safety performance. For instance, the standard dictates that a 2.5mm² copper conductor must not exceed 7.41 ohms per kilometer (for Class 2 stranded). This precise limit prevents the use of sub-standard materials and ensures that voltage drop and heat generation remain within safe limits. This precise limit prevents the use of sub-standard

If you measure a 50 m length of 2.5 mm² cable and get more than 0.37 Ω (7.41 Ω/km × 0.05 km), the conductor fails the standard. including the arrangement of conductors

One of the most significant contributions of BS EN/IEC 60228 is the establishment of the metric "mm²" standard for cross-sectional area. This replaced older imperial measurements. The standard sets out a series of preferred sizes (e.g., 1.5mm², 2.5mm², 4.0mm²).