Multilayer of LV cables directly in the ground

[Vlad.M]

Hi guys,

Is there a right way to calculate the reduction factor like in table B.52.18 as in standard IEC 60364 but for 2 layers of cables?

is it possible that in official standard there are no guide line for that case?

cheers.

 

[7anoter4]

You are right. For one row of 5 cables, you can use the tables, but not for two rows.
A remark about IEC 60364-5-52 standard at first.
Annex B it is only informative, and the ampacities shown here are in order to exemplify a new mode of presentation and these are not correct values.
The A annex is still for calculations. See, at first one of the following tables:
Table A.52-2 (52-C1) – Current-carrying capacities in amperes for methods of installation in table A.52-1 (52-B1) – PVC insulation/two loaded conductors/copper or aluminum Conductor temperature: 70 °C/Ambient temperature: 30 °C in air, 20 °C in ground –column D, or:
Table A.52-3 (52-C2) – Current-carrying capacities in amperes for methods of installation in table A.52-1 (52-B1) – XLPE or EPR insulation/two loaded conductors/copper or aluminum Conductor temperature: 90 °C/Ambient temperature: 30 °C in air, 20 °C in ground –column D.
And then see:
Table A.52-18 (52-E2) – Reduction factors for more than one circuit, cables laid directly in the ground –
for 5 cables [of 2 conductors] 0.125 m apart. kred=0.65
For two rows of 5 cables per each row you have to calculate the current carrying capacity according
to IEC 60287-2-1 [and 1-1].

 

[7anoter4]

DIN VDE 0276-1000 presents a table of conversion factors as per attached sketch.

 

[Vlad.M]

thank you,
in my case we plan to use 2 single core 150 mm2 NA2XY.

 

[7anoter4]

Table A.52-3 (52-C2) is calculated per IEC 60287-2-1 and 1-1.
The column D it is for 2 cables in a duct in 2.5 K.m/W Earth thermal resistivity and 0.7 m depth in a duct.
Reference method D, item 70 of table 52-3, (multi-core cable in ducts in the ground):
Cable drawn into plastic, earthenware or metallic ducts laid in direct contact with soil having a thermal resistivity of 2.5 K.m/W and a depth of 0.7 m.
According to your sketch there are two single core cables touching but without any pipe [or duct].
[so Rsd=0 and 110 cm depth]. Let’s say the resistivity stays 2.5 K.m/W.
The calculation according to IEC 60287-2-1 is very simple taking into consideration the cable data-conductor diameter 15 mm, insulated core diameter 17.8 mm and the jacket diameter of 21.2 mm.
The ampacity -per each cable-is then 120.7A.
Following DIN-VDE [from ABB vol.11-E-13] table 13-44, for 3 single core cables in triangle, aluminum I=305 A. From table 13-54 for XLPE, 20oC, 2.5 K.m/W, load factor 1[100%] f1=0.81. From table 13-56 for 10 systems 7cm apart f2=0.44. Then for 10 groups of 3 cables we get 305*0.81*0.44=108.7 A

 

[7anoter4]

The last two tables are:13-54 and 13=56

 

[7anoter4]

I'll try now again

 

[Vlad.M]

interesting, thank you for the explanation.
if it is not too much to ask, can you please share the tables: Table A.52-3 (52-C2) and table 52-3?

appreciate your help.

 

[7anoter4]

You said:
"can you please share the tables: Table A.52-3 (52-C2) and table 52-3?"
What it is "table 52-3"?

 

[Vlad.M]

nevermind, I tought you referanced a table from IEC 60287-2-1 and 1-1.

thanks for the help.