Imperfect contact thermal factor

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

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
$F_{k}$
Used in
$\epsilon_{k}$
$M_{k}$
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