Cross section of a cable
It would appear that the first row of the table refers to a stranded wire where the total cross-sectional area of the conductor (i.e., &quot;Nominal section&quot;) equals 2.5 mm2 (roughly AWG13). It is made up of 50 strands of 0.25 mm diameter wire (about AWG30).
The diameter of a solid 2.5 mm2 wire would be 1.78 mm. A stranded wire is somewhat larger, around 2.0 mm (roughly 8 layers of the 0.25 mm wire). This conductive core is surrounded by 0.75 mm of &quot;insulation&quot; and 0.80 mm of &quot;sheath&quot;, for a total diameter of 5.1 mm for the wire plus all of its coatings.