IEC60364-5-52 Tabel B.52.18

[wml9]

Hi,

I need advice for determining the derating factor in IEC60364-5-52 Table B.52.18.

I will be having 20 DC cables direct buried and lay flat with one cable diameter apart as shown in the link below.

https://files.engineering.com/getfi...-3cbd-4cab-8be4-44618240bbb8&file=Capture.PNG

Which grouping derating factor should I consider in Table B.52.18 (

https://files.engineering.com/getfi...hatsApp_Image_2020-11-05_at_5.58.11_PM.jpeg).

Thank you in advance.

 

[RRaghunath]

In the sketch, I see 20 circuits, i.e. 20 sets of cables each comprising of +ve & ve cable set.
If you are using single core cables (as it seems from sketch), don't space the cables of same circuit. That is keep the +ve & -ve cable of the same circuit together.
The spacing of one cable dia shall apply between the circuits and the corresponding derating factor is 0.35 from the table in the IEC code.
Spacing between +ve and -ve cable of the same circuit may lead to eddy currents (and resultant heating) in the metallic structures close to the trench whenever there is variation in the current flow.

 

[7anoter4]

There are 2 possibilities:
1)consider 2-conductor cable and treat it as 10 cables.
Let's say 120 square mm copper pvc insulated 2 conductors underground: 246 A [IEC 60364-5-52] . 12 cable 0.42 derating I=246*0.42=103.32 A.
2)20 circuits single core cables.
Since IEC 60364-5-52 does not present a table with single core cable, you have to calculate the rating of single core buried cable using IEC 60287-2-1 and IEC 60287-1-1. The conductor diameter and 20oC resistance from IEC 60228. Insulation and sheath [if any] according to IEC 60502-1 [low voltage].
I did now this calculation for the above-mentioned cable and I get 311 A. Multiply this by 0.35 for 20 cables I get 109 A [5.5% more]