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Buried ducts for medium voltage cables

vici
Hello everyone,


Is there any BS or IEC standard indicating typical configurations for multiple ducts buried in the ground? This is mainly in relation to medium voltage cables.


Specifically, I wondered if there was a standard giving guidance on typical arrangements used for multiple ducts to be laid in the ground (e.g ducts arrangement like 3 x 5 or 4 x 4) and backfilling material requirements (e.g. ducts surrounded by concrete or other back fill materials etc..). I am aware of all the minimum depths form the ground level, depending on the conditions (e.g. carriageways, footways, arable land etc..) but I wondered if there were also indications from BS or IEC documents for typical layouts / engineering solutions.


thank you
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  • Former Community Member
    0 Former Community Member
    The duct disposition will tend to reflect your selected arrangement for cables (grouping and/or use of single core cables as opposed to multicores) - in most cases, you would be looking for either flat layered ducts or trefoil arranged ducts. The duct grouping may well also need to reflect the drawing in arrangements. There is no point having four layers of ducts arrive at a chamber if you cant physically draw anything into the lower layers if the upper layers impede that with existing cabling


    Backfill might well be influenced by the nature of the excavated material - so you may want to swap particularly peaty material (which is an excellent thermal insulator) for quartz material (sand or stonedust - which is a particularly goof thermal conductor. It might also be influenced by the fact that the excavated material is full of sharp and /or hard bits - you wouldn't want to bed cable (or ducts) in that without screening it


    Think about the ground resistivity factor in your previous post regarding BICC Ratings


    Don't be overly obsessed about ducting MV cabling - it is often better buried direct and ducting only used for areas where future excavation might be very difficult - unless you have contaminated soil of course


    There are several "preferred" arrangements but nothing that you could specifically link to a "standard"  - for depths, the NJUG documentation is useful but it sounds like you have that anyway


    Regards


    OMS



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  • Former Community Member
    0 Former Community Member
    The duct disposition will tend to reflect your selected arrangement for cables (grouping and/or use of single core cables as opposed to multicores) - in most cases, you would be looking for either flat layered ducts or trefoil arranged ducts. The duct grouping may well also need to reflect the drawing in arrangements. There is no point having four layers of ducts arrive at a chamber if you cant physically draw anything into the lower layers if the upper layers impede that with existing cabling


    Backfill might well be influenced by the nature of the excavated material - so you may want to swap particularly peaty material (which is an excellent thermal insulator) for quartz material (sand or stonedust - which is a particularly goof thermal conductor. It might also be influenced by the fact that the excavated material is full of sharp and /or hard bits - you wouldn't want to bed cable (or ducts) in that without screening it


    Think about the ground resistivity factor in your previous post regarding BICC Ratings


    Don't be overly obsessed about ducting MV cabling - it is often better buried direct and ducting only used for areas where future excavation might be very difficult - unless you have contaminated soil of course


    There are several "preferred" arrangements but nothing that you could specifically link to a "standard"  - for depths, the NJUG documentation is useful but it sounds like you have that anyway


    Regards


    OMS



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