Factor to account for imperfect thermal contact between conductor or screen, sheath or armour and surrounding or adjacent non-metallic materials.

• 0.7 is recommended for most cases.
• 1.0 is used for conductor and screen of oil-filled cables.
• 0.9 can be used when the metallic component is completely bonded on one side to the adjacent medium (e.g. aluminium foil to oversheath).
• 0.5 is used for isolated screen wires, not fully embedded, situated under an extruded tube and air spaces are present between the wires.

Screen wires are considered isolated if the wires cover <70% of the circumference. Isolated screen wires are considered fully embedded if they are separated by at east one wire diameter and fully surrounded by non-metallic materials, then a value of 0.7 can be used, otherwise 0.5.

Symbol
$F_{\mathrm{k}}$
Unit
-
Used in
$\epsilon_{\mathrm{k}}$
$M_{\mathrm{k}}$
Choices
ValueCase
1.0for conductor and screen of oil-filled cables
0.9if completely bonded on one side
0.7recommended value
0.5for isolated screen wires, not fuly embedded