Thermal insulation in cable calculations

[ringer]

When doing cable calcs, particularly the Ci for thermal insulation when calculating It, does the amount of thermal insulation refer to the length of cable that is covered by (any thickness of) insulation, or does it refer to the thickness of the insulation that is applied over (any part of the length of) the installed cable?

 

[telectrix]

523.7 refers to the length of cable surrounded by insulation.

 

[ringer]

523.7 refers to the length of cable surrounded by insulation.

I think you mean 523.9 Tel

I have been getting confused because 523.9 and table 52.2 specifically refer to the length of cable in the insulation, yet table 4D5 gives CCC for Ref Method 100 (covered by thermal insulation not exceeding 100mm in thickness) values as being almost exactly 0.78 the value of ref method C (table 52.2 gives derating factor of 0.78 for length in insulation of 100mm)

 

[Guest123]

Table 52.2 gives the derating factors for the length of cable covered by insulation in comparison to method c, clipped direct.

If you then look at table 4D5, and compare method c with method 103 you will see the ccc differs by exactly 0.5 which relates back 523.9, 3rd paragraph i.e a cable surrounded by insulation for a length of greater than 0.5M should be derated by 0.5x.