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Ampacity problem for cables underground ( IEC )

Ampacity problem for cables underground ( IEC )

Ampacity problem for cables underground ( IEC )

(OP)
IEC 60364-5 Table A52-3 has a list of installation options for cable ampacities. It shows Items 70 through 73 as reference D ( underground in counduit, underground directly buried etc. )

Then I check PVC ( 70C )3 core cable ampacities, ( Table B52-4 Col7.)

It shows 122 Amps for 50 mm2 cable. ( NEC 310-16 1/0 gives 150 for directly buried at 75 C )

Then I check cable manufacturer's data sheets. The values are much much higher than IEC.

They list 188 Amps in ground ( Pyrsmian ) and 153 in air ( I really didn't understand how ground would have higher ampacity ). It also says "Current carrying capacities are valid at 20C earth temperature, 30C air temperature, 1 KM/W and 0,7 continous loading (cylic)"

Another problem with IEC's reading ( or my misunderstanding ) all underground insallations ( D installation ) give same ampacities ( eather directly buried, or in a conduit , or a cable duct underground ).

Any answers and ideas would be appreciated, and which value would be good to use ?







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