Number of loaded cables in the backfill area $N_b$ is calculated individually for every cable or duct as the total losses in the backfill area divided by the losses in the specific cable or duct with multi-core cables and cables in a common duct treated as a single loaded cable. Hence, $N_b$ is not necessarily an integer number.

Symbol
$N_{\mathrm{b}}$
Unit
-
Used in
$T_{\mathrm{4db}}$