The ratio of heat dissipation coefficients for group of cables in air is according to IEC 60287-2-2
$1.41$ | 2 cables or ducts, side by side, $e_{hor}/Do_d$ < 0.5 |
$1.65$ | 3 cables or ducts, side by side, $e_{hor}/Do_d$ < 0.75 |
$1.2$ | 2 trefoils, side by side, $e_{hor}/Do_d$ < 1 |
$1.25$ | 3 trefoils, side by side, $e_{hor}/Do_d$ < 1.5 |
$1.35$ | 2 cables or ducts, one above the other, $e_{ver}/Do_d$ < 0.5 |
$1.085\left(\frac{e_{ver}}{Do_d}\right)^{-0.128}$ | 2 cables or ducts, one above the other, $e_{ver}/Do_d$ < 1.89 |
$1.57$ | 3 cables or ducts, one above the other, $e_{ver}/Do_d$ < 0.5 |
$1.19\left(\frac{e_{ver}}{Do_d}\right)^{-0.135}$ | 3 cables or ducts, one above the other, $e_{ver}/Do_d$ < 3.62 |
$1.39$ | 2 pair/trefoil, one above the other, $e_{ver}/Do_d$ < 0.5 |
$1.106\left(\frac{e_{ver}}{Do_d}\right)^{-0.078}$ | 2 pair/trefoil, one above the other, $e_{ver}/Do_d$ < 3.63 |
$1.57$ | 3 pair/trefoil, one above the other, $e_{ver}/Do_d$ < 0.5 |
$1.19\left(\frac{e_{ver}}{Do_d}\right)^{-0.135}$ | 3 pair/trefoil, one above the other, $e_{ver}/Do_d$ < 3.63 |
$1.23$ | near to a surface, $e_{wall}/Do_d$ < 0.5 |
$1$ | otherwise |