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Cables buried direct in ground...

Martyn

Hi Folks,

I have been giving a bit of thought to direct buried cables and was looking around for the ‘Best’ method for installation in reference to current carrying capacity especially with the rise in copper prices. 96A vs. 152A on something as small as a 25mm 4c or 365A Vs 592A on a 300mm 4c.

The differences between ERA & BS7671 figures are significant and they seem to come down to actual installed conditions, for example ERA have an assumed thermal resistivity of 1.2k.W/m vs. that of BS7671 which uses 2.5k.W/m.

I got to thinking is there an installation method that could be more readily assured to be better in terms of thermal resistivity?

Damp compacted sand would seem to be the best for decreasing thermal resistivity, but how much? would a liner in the base of the trench be of any use to reduce drying or migration of the sand or might this just add to the overall thermal resistivity?

I read this earlier https://ictinternational.com/casestudies/underground-power-cable-installations-soil-thermal-resistivity/ 

And then what about the ‘New’ Conducrete? could encasing in such material have significant benefits or might this risk damage with settlement?

Thoughts?

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    I gave this much thought in the context of my self-build chum's distribution circuit to the house and we did discuss it in here. In the event, he took the view that 25 sqmm was not much more expensive than 16 sqmm and perhaps his cautious nature overcame his parsimony which would make a Yorkshireman appear to be the soul of generosity. (I cursed him a bit when it came to terminating the larger size.)

    The property is in the South Lakes and at the bottom of a hill with a spring elsewhere on the plot, so I have no doubt that the thermal resistivity of the soil is low. However, without being able to measure it, I felt obliged to comply with BS 7671.

    So an interesting question and perhaps it is like diversity: a range of opinions will exist.

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  • 0

    I gave this much thought in the context of my self-build chum's distribution circuit to the house and we did discuss it in here. In the event, he took the view that 25 sqmm was not much more expensive than 16 sqmm and perhaps his cautious nature overcame his parsimony which would make a Yorkshireman appear to be the soul of generosity. (I cursed him a bit when it came to terminating the larger size.)

    The property is in the South Lakes and at the bottom of a hill with a spring elsewhere on the plot, so I have no doubt that the thermal resistivity of the soil is low. However, without being able to measure it, I felt obliged to comply with BS 7671.

    So an interesting question and perhaps it is like diversity: a range of opinions will exist.

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