Proximity effect factor of conductors

The formulae are accurate providing $x_p$ does not exceed 2.8, and therefore applies to the majority of practical cases.

Symbol
$y_p$
Formulae
$0$one single-core cable
$\frac{2.9{x_p}^4}{192+0.8{x_p}^4} \left(\frac{d_c}{s_c}\right)^2$Two-core cables and two single-core cables
$\frac{2.9{x_p}^4}{192+0.8{x_p}^4} \left(\frac{d_x}{s_c}\right)^2$Two-core cables with sector-shaped conductors
$\frac{{x_p}^4}{192+0.8{x_p}^4} \left(\frac{d_c}{s_c}\right)^2 \left(0.312\left(\frac{d_c}{s_c}\right)^2+\frac{1.18}{\frac{{x_p}^4}{192+0.8{x_p}^4}+0.27}\right)$Three-core cables and three single-core cables
$\frac{\frac{2}{3} {x_p}^4}{192+0.8{x_p}^4} \left(\frac{d_x}{s_c}\right)^2 \left(0.312\left(\frac{d_x}{s_c}\right)^2+\frac{1.18}{\frac{{x_p}^4}{192+0.8{x_p}^4}+0.27}\right)$Three-core cables with sector-shaped conductors