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

Symbol
$h_{\mathrm{lg}}$
Unit
-
Formulae
$1.41$2 cables or ducts, side by side, $e_{\mathrm{hor}}/Do_{\mathrm{d}}$ < 0.5
$1.65$3 cables or ducts, side by side, $e_{\mathrm{hor}}/Do_{\mathrm{d}}$ < 0.75
$1.2$2 trefoils, side by side, $e_{\mathrm{hor}}/Do_{\mathrm{d}}$ < 1
$1.25$3 trefoils, side by side, $e_{\mathrm{hor}}/Do_{\mathrm{d}}$ < 1.5
$1.35$2 cables or ducts, one above the other, $e_{\mathrm{ver}}/Do_{\mathrm{d}}$ < 0.5
$\frac{1.085}{\left(\frac{e_{\mathrm{ver}}}{Do_{\mathrm{d}}}\right)^{0.128}}$2 cables or ducts, one above the other, $e_{\mathrm{ver}}/Do_{\mathrm{d}}$ < 1.89
$1.57$3 cables or ducts, one above the other, $e_{\mathrm{ver}}/Do_{\mathrm{d}}$ < 0.5
$\frac{1.19}{\left(\frac{e_{\mathrm{ver}}}{Do_{\mathrm{d}}}\right)^{0.135}}$3 cables or ducts, one above the other, $e_{\mathrm{ver}}/Do_{\mathrm{d}}$ < 3.62
$1.39$2 trefoils, one above the other, $e_{\mathrm{ver}}/Do_{\mathrm{d}}$ < 0.5
$\frac{1.106}{\left(\frac{e_{\mathrm{ver}}}{Do_{\mathrm{d}}}\right)^{0.078}}$2 trefoils, one above the other, $e_{\mathrm{ver}}/Do_{\mathrm{d}}$ < 3.63
$1.23$near to a surface, $e_{\mathrm{wall}}/Do_{\mathrm{d}}$ < 0.5
$1$otherwise
Related
$Do_{\mathrm{d}}$
$e_{\mathrm{hor}}$
$e_{\mathrm{ver}}$
$e_{\mathrm{wall}}$
Used in
$h_{\mathrm{T4}}$