Factor between AC and DC resistance armour

Get the a.c. resistance of magnetic steel armour wire from the d.c. resistance depening on the wire diameter according to IEC 60287-1-1, clause 2.4.2.1

Symbol
$f_{ar}$
Unit
$\Omega$/m
Formulas
$\frac{1.4-1.2}{5-2} \left(t_{ar}-2\right)+1.2$
Related
$t_{ar}$
Used in
$R_{ar}$