# Ratio of heat dissipation coefficients

The ratio of heat dissipation coefficients for group of cables in air is according to IEC 60287-2-2 Ed.1.0

Symbol
$h_{lg}$
Formulae
 $1.41$ 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 trefoils, one above the other, $e_{ver}/Do_d$ < 0.5 $1.106\left(\frac{e_{ver}}{Do_d}\right)^{-0.078}$ 2 trefoils, one above the other, $e_{ver}/Do_d$ < 3.63 $1.23$ near to a surface, $e_{wall}/Do_d$ < 0.5 $1$ otherwise
Related
$Do_d$
$e_{hor}$
$e_{ver}$
$e_{wall}$
Used in
Image
IEC standard 60287-2-2 Ed. 1.0 (1995) Table 1