This layer is added on top of the serving/jacket. It may be a semi-conducting layer or a flame retardant added during extrusion process or a flame retardant paint being applied after installation. For calculations, the additional layer has the same material properties as the serving/jacket.

Symbol
$t_{\mathrm{jj}}$
Unit
mm
Related
$t_{\mathrm{j}}$
Used in
$A_{\mathrm{j}}$
$D_{\mathrm{e}}$
$t_{\mathrm{3}}$