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