Hi guys. Was doing a cable calc and got confused with Ci and reference method 103. Are they essentially the same, but that method 103 seem to be calculated for insulation at 200mm thick, whereas Ci allows you to vary correction for different thicknesses of insulation?
Also, when using It >=In/(CaCgCiCc), and part of that cable is in, say reference method B, do we just asses which calculation gives worst case and apply that?, we don't combine them do we?
Cheers.
Although the values for method 103 in
Table 4D5 are half those for method 3 (clipped direct), this does NOT mean that Ci (thermal insulation de-rating factor) in the calculation =1, i.e. no de-rating is applied. This is because the calculated It is the minimum tabulated cable current required, which will be compared with actual worst case tabulated cable currents (due to being half the method 3 values) for various specific T&E cable sizes in order to select a cable that is =>It
Ci is the thermal insulation de-rating factor selected from
523.7, and used in the calculation to find the minimum tabulated cable current required It=>In/CaCgCiCcCt
Select each de-rating factor for the worst case situation the cable run will encounter. So, for example, if a 70°C thermoplastic T&E cable runs through areas with ambient temperatures of 20°C, 40°C and 60°C, select 60°C the worst case, and apply the corresponding de-rating factor from
Table 4D1 of Ca=0.5
Repeat the worst case selection for each de-rating factor in turn.
If part of your cable run is thoroughly surrounded by thermal insulation, indicating installation method 103. If the length of the insulation is below <400mm the de-rating factors in
Table 52.2 can be used for Ci, if longer than 400mm Ci=0.5
Having calculated a minimum It (say the minimum for our example cable =>35A) we go to
Table 4D5 and look for a tabulated It in the column titled Reference Method 103 that is =>35A, selecting 4mm[SUP]2[/SUP] T&E It=37A for our application.
