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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
Parents
  • Former Community Member
    0 Former Community Member
    Not really - you are concerned about minimum depth of cover (for avoidance of casual digging hazards) and maximum depth to lowest duct as it can quickly lead to some very deep chambers which rapidly need both proper access arrangements (step irons etc) and can often become "confined spaces" with all the attendant issues


    Under carriageways, then you know the probable axle weight of typical road vehicles (if not you could assume a minimum of 400kN presumed from a D400 chamber cover) and calculate your risk of surcharging the duct at a range of depths. In other applications you might be assuming anything up to 900kN (typical of heavy plant yards or aircraft aprons)


    I'm not aware of a "on size fits all" set of standards - depending on the contractual arrangements I would determine the electrical design and then pass the ducting problem to a civil engineer (just check he understands the equation that water and dirt equals mud) and you'll be good to go. Give him chamber sizes to aim for that meet your bending radii criteria, though  - they often fail to understand that as you approach the chamber edge, the radii get smaller. And ask for soakaways or positive drainage from the chambers - you don't want to lift a lid one day, to be presented with all your cabling submerged under filthy water


    Regards


    OMS


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  • Former Community Member
    0 Former Community Member
    Not really - you are concerned about minimum depth of cover (for avoidance of casual digging hazards) and maximum depth to lowest duct as it can quickly lead to some very deep chambers which rapidly need both proper access arrangements (step irons etc) and can often become "confined spaces" with all the attendant issues


    Under carriageways, then you know the probable axle weight of typical road vehicles (if not you could assume a minimum of 400kN presumed from a D400 chamber cover) and calculate your risk of surcharging the duct at a range of depths. In other applications you might be assuming anything up to 900kN (typical of heavy plant yards or aircraft aprons)


    I'm not aware of a "on size fits all" set of standards - depending on the contractual arrangements I would determine the electrical design and then pass the ducting problem to a civil engineer (just check he understands the equation that water and dirt equals mud) and you'll be good to go. Give him chamber sizes to aim for that meet your bending radii criteria, though  - they often fail to understand that as you approach the chamber edge, the radii get smaller. And ask for soakaways or positive drainage from the chambers - you don't want to lift a lid one day, to be presented with all your cabling submerged under filthy water


    Regards


    OMS


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