Inclination derating factor

In the case of inclined ducts, it is important to consider that the methods for determining $T_4$. The IEC standards assume that a 1 m cable length equates to a 1 m length of ground surface for the heat to be dissipated from. This assumption is violated for inclined ducts, and the effect should be taken into account.

For example: in case of a 45 degrees inclined duct, then 1 m of cable equates to 0.71 m of ground surface, and hence, $T_4$ should be increased by a factor of 1.41.

Symbol

$F_{\alpha}$

Unit

p.u.

Formulae

$\frac{1}{cos\left(\frac{\alpha_{sys} \pi}{180}\right)}$

Related

$\alpha_{sys}$

Inclination angle in degrees [°]

$\pi$

Archimedes' constant $\pi$

Used in

$T_{4i}$

Thermal resistance of medium in the duct [K.m/W]

$T_{4ii}$

Thermal resistance of the duct wall [K.m/W]

$T_{4\mu}$

Thermal resistance to ambient [K.m/W]