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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
$Do_d$
Outer diameter of duct [mm]
$e_{hor}$
Horizontal clearance [mm]
$e_{ver}$
Vertical clearance [mm]
$e_{wall}$
Clearance to wall [mm]
Used in
$h_{T4}$
Ratio of thermal resistance to ambient
Image
IEC standard 60287-2-2 Ed. 1.0 (1995) Table 1