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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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    Martynduerden: 
    Not too sure on Auckland 60 & 30 year old cables at the time, the older lot failed stressing the ‘newer’ ones I believe, I thought they decided it was poor maintenance of cables that ought to have long been replaced?

    It is self-evident that if one of a pair of cables in parallel fails, the other will be overloaded.

    I sincerely hope that cables last more than 30 years. Our service cable is at least 39 years old; the transformer dates from 1959; and there is a map of the cables in the Hampshire Archives which is pre-war.

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  • 0

    Martynduerden: 
    Not too sure on Auckland 60 & 30 year old cables at the time, the older lot failed stressing the ‘newer’ ones I believe, I thought they decided it was poor maintenance of cables that ought to have long been replaced?

    It is self-evident that if one of a pair of cables in parallel fails, the other will be overloaded.

    I sincerely hope that cables last more than 30 years. Our service cable is at least 39 years old; the transformer dates from 1959; and there is a map of the cables in the Hampshire Archives which is pre-war.

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