Attainment factor for groups of cables

This is the attainment factor for groups of cables the cable or duct external surface, i.e. the ratio of the temperature rise at time i to the rise in the steady state.This function is used in calculating cyclic rating factor for groups of cables.

Note: The parameters $L_{cm}$ and $D_o$ are in meters.

Symbol
$\gamma_{t}$
Formulae
$\frac{\left(N_{c} - 1\right) \left(\operatorname{expi}{\left(- \frac{L_{cm}^{2}}{\delta _{soil} \tau} \right)} - \operatorname{expi}{\left(- \frac{d_{f}^{2}}{16 \delta _{soil} \tau} \right)}\right) - \operatorname{expi}{\left(- \frac{D_{o}^{2}}{16 \delta _{soil} \tau} \right)} + \operatorname{expi}{\left(- \frac{L_{cm}^{2}}{\delta _{soil} \tau} \right)}}{2 \ln{\left(\frac{4 F_{eq} L_{cm}}{D_{o}} \right)}}$
$D_{o}$
$\delta _{soil}$
$L_{cm}$