Standard Cable Sizes

[urjaengrs]

I would like to know regarding standard cable size. Who defines it, i mean which standar has defined this. Is somebody is aware why the standard concluded for a particular size. For exampl, why cable size is of 70 sq.mm. only and not 75 sq.mm.

In advanse thanks..........

 

[1x1x1x]

Additionally the factor a (7)sqrt(10) = 1.39 is also used e.g. 25mm^2*1.39 = 35 mm^2 ; 50mm^2*1.39 =70mm^2; etc.