Cable de-rating factors

[power2020]

Dear Folks,
Please clarify the following:
How power Cable "ambient temperature de-rating factor" will depend on different protection systems?
In one of the cable catalogues it is given as follows:
for Example:
Ambient temp: 50 deg.C
Semi enclosed fuse to BS 3036 : 0.91 (Derating factor)
Fuse to BS 88 or BS 1361, or circuit breaker to BS 3871 part 1 : 0.82 (derating factor)
Advanced thanks...

 

[cuky2000]

The cable current capacity in general is a direct function of the maximum allowable temperature to avoid insulation damage or conductor annealing or fusing.

For insulated cable, there are several limiting factor such as ambient temperature, number of cable and characteristic of the raceway, protective device speed during short circuit, insulation and conductor materials, etc.

Enclosed is a diagram SC illustrating some of the current derating effects:

http://cuky2000.250free.com/Cable_SC_IEEE-Std-242.jpg

 

[power2020]

Thank you cuky2000 for your reply,
As of my knowledge, Protective device rating will depend on cable short-circuit capacity but not on ambient temp of the cable.
But one of the leading cable manufacturer given different de-rating factors for using different protective devices for the same ambient temp. (let us say at 50deg.C)