The thickness of core insulation is including screening tapes plus half the thickness of any non-metallic tapes over the laid up cores.

This is used for two types of three-core oil-filled cables with circular conductors and circular oil ducts between the cores.

1. with metallized paper core screens, where the thickness is including carbon black and metallized paper tapes
2. with metal tape core screens, where the thickness is including the metal screening tapes

Symbol
$t_{\mathrm{i}}$
Unit
mm