Mean distance between the phases

This is the geometric mean distance between phases.

In case of three single-core cables in flat formation, equal distance, with regular transposition, this becomes the equation $2 \sqrt[3]{2}\cdot s_{c}$ as it is used in IEC 60287-1-1, chapter 2.3.2.

Symbol
$a_m$
Unit
mm
Formulae
$L_{earth}$single-phase system
$s_c$two-phase system
$\left(a_{12} a_{23} a_{31}\right)^{\frac{1}{3}}$three-phase system