Document Sample
Electricity Powered By Docstoc

                      Technical Sheet

                                     November 2004

Ministry of Housing and Lands
                                                                                                TECHNICAL SHEET


      Before any development or                            Designs for the provision of electrical supplies to
      building permit is issued the                        developments will be prepared by the Central Electricity
      CEB must be provided with                            Board (CEB) on a case-by-case basis and the developer is
      full and accurate details of                         urged to hold early discussions with the CEB to confirm that
            what is proposed.                              the cost of provision is likely to be acceptable.
      A written statement must be                          There are however, general requirements and guidance
     secured from the CEB stating                          that should be considered by prospective developers when
     that they have no objections                          preparing development schemes.
      to the development. A “No
      Objection” statement does                    Method of Supply
       not mean that electricity
                                                           For new morcellement development and other major
      can be provided easily and
                                                           developments the preference is for underground supply of
      the developer needs to be
                                                           electricity. In main urban centres where the existing network
      aware that the provision of
                                                           is already underground any extension of the network will also
       electricity could be very
                                                           have to be laid underground.

                             O      Services overhead - more vulnerable to cyclone damage, likelihood of more
                                    outages, more visually intrusive.

                                    Undergrounding of services - less susceptible to damage, less visually intrusive,
                            P       opportunities to use public space for other things, but more expensive.

Ministry of Housing and Lands, November 2004
                                                                                      TECHNICAL SHEET


                                                     In lower value developments an overhead supply may
                                                     be appropriate but this manner of supply is vulnerable to
                                                     cyclone damage, likely to be subject to more frequent
                                                     outages and is visually more intrusive than an underground

                                               Main Transmission Cables
                  rv r

                                                     The main transmission network consists of 132kV or 66kV


                                                     lines (both currently operating at 66kV). The former are

                                                     pylon mounted whilst the latter may be either pylon or pole
                                                     mounted. A minimum lateral clearance of 7.5m is required
    Main Transmission Cable
    Clear Servitude
                                                     from the outermost conductors, but for pylon mounted
                                                     cables, which are more widely spaced than poles, an
                                                     additional clearance is required to allow for cable swing due
                                                     to the wind. Consequently a clear servitude of approximately
                                                     26m is required under main transmission lines.
                                                     The ground below main power cables can be utilised for
                                                     open space, car parking or agriculture but no trees should be

                                               Main Feeder Cables
                                                     Generally main 22kV Feeder cables will be installed using
                                                     overhead bare wire conductors. Outermost conductors are
                                                     set a distance of 1.2m from the centreline of poles. A lateral
                                                     clearance of 4m is required to any building from these bare
                                                     wire conductors.
              Plot            Plot
                                                     Boundary walls may be constructed within the line of the
                                                     outermost bare wire conductor providing minimum vertical
                        Transformer                  clearances of 4m are maintained.

                                               Underground Supply
                                                     From the 22kV feeder supply the HV connection to the
    Allow space for the provision of                 development should be laid directly in the ground within
    transformer sub-stations                         the utility reserve. Supply crossings under roads should be
                                                     laid in ducts encased in concrete. Where cables have to
                                                     cross roads, draw-pits will be required on either side of the
                                                     road. These draw-pits should be approximately 2.2m square
                                                     and consequently take up a lot of space. The utility reserve
                                                     may need to be wider at these locations to ensure that
                                                     other services such as road drains and water supply can be

Ministry of Housing and Lands, November 2004
                                                                                             TECHNICAL SHEET


           Uninsulated overhead cables
                 1.2m               1.2m

                                                                   4.0m minimum from
                                                                  uninsulated cable to
                                                                 buildings, structures and
                                                                         trees etc


                                                     0.6m - 1.7m
                                                                  Telecom trench

                                                                                             Intrusion into minimum reserve
                                               Water                                         at ground level requires
                                               Drain                                         agreement with the Ministry
                                                                                             of Public Utilities (Central
                                                                                    0.6m     Electricity Board)

                                                                1.2m             1.2m
                                                                Overhead clearance

                                               Total Utility Reserve width 1.7m - 2.9m         4m minimum clearance to
    Minimum clearance and
    indicative reserve requirements
    for uninsulated overhead cables
    alongside other services

Ministry of Housing and Lands, November 2004
                                                                                     TECHNICAL SHEET


              500mm                                 Transformer sub-stations are required to reduce the supply
              minimum                               voltage to the level required by consumers (generally 400/230
                                                    volts). The maximum length of low voltage cable between
                                                    a consumer and the sub-station that serves it is 500m. Sites
                                                    for the installation of CEB sub-stations will need to be allowed
                                                    for within the development, with an area of approximately
                                                    5m x 6m being required for each. To ensure that sub-station
                                                    locations and cable routes are laid out as efficiently as
                1.5m minimum                        possible the developer should hold early discussions with CEB.
                                                    From sub-stations a 400V supply cable should be laid directly
                                                    underground to the various distribution pillars from which
                                                    customers are supplied with 230V individual connections.
                                                    Each distribution pillar typically serves up to 16 plots (8 each
    Minimum distances from
                                                    side of the road) through cables laid in individual 63mm
    insulated electricity cables
                                                    diameter cable ducts. Where these ducts cross under roads
                                                    they should be encased in concrete. The distribution pillars
                                                    should normally be located on the boundary between two
                                                    plots and close to the plot side of the road reserve.
                                                    Separate street lighting provision (poles or wall mounted) will
                                                    also be required. The developer will be responsible for the
                                                    provision, erection, cabling to and commissioning of street

                                               Overhead Supply
                                                    All overhead supplies to developments will be made using
                                                    insulated cables bunched into a single unit and strung
                                                    between electricity poles. Space should be provided within
                                                    utility reserves for pole planting (typically 600mm minimum).
                                                    Buildings, trees or other structures will need to be positioned
                                                    to provide safe clearances to cables. A minimum lateral
                                                    distance of 0.5m and vertical distance of 2m is required to
                                                    insulated cables.
                                                    In addition to allowing for space to plant the poles, the
                                                    developer also needs to be aware that where changes of
                                                    direction of the cables occur it will be necessary to use pole
                                                    staying cables. These cables will need to be placed on the
                                                    outside of the bend or junction and will need to be fixed
                                                    approximately 5m outside the line of the poles. Where the
                                                    support stay would be required on the road side of the pole
                                                    then it either will be necessary to:
                                                       • Transmit the load to another pole on the opposite side
                                                         of the road and then provide a support stay to this
                                                         pole, or
                                                       • Carry the cables to a stayed pole on the other side of
                                                         the road and back again.
                                                    Consideration of the impact on other utilities and pedestrian
                                                    and vehicular access should be given.

Ministry of Housing and Lands, November 2004
                                                                                        TECHNICAL SHEET


                                                      In small or very low-cost developments, use may be made of
                                                      pole-mounted transformers, but the preference is for ground
                                                      mounted transformer sub-stations. Ground mounted sub-
                                                      stations will require suitable sites to be provided as for an
                                                      underground supply.
                                                      The low voltage cables will generally be hung on the same
                                                      poles as the HV cables with individual properties supplied
                                                      through separate connections laid in 63mm diameter ducts
                                                      fixed to the poles and then run underground to customers on
                                                      either side of the street. Typically 4 properties are served per
                                                      pole and poles should normally be planted at every other
                                                      property boundary, depending upon frontage sizes. The
                                                      maximum spacing for poles carrying insulated cables is 40m.
                                                      Where plot spacing is greater or less than 20m then the pole
                                                      spacing is adjusted so that a pole is planted at every plot
                                                      Where overhead transformers are used, these are most
                                                      efficiently located at street corners, from which all the
                                                      interconnecting streets can be supplied with direct cable
                                                      runs. However, overhead transformers are unsightly and it
                                                      may be better, where they have to be used, to locate them
                                                      in side-streets and accept the greater density of cables
                                                      bunched on the poles.

                                               Supplies to Individual Buildings in Built-up Areas
    The developer will be
    required to ensure that                           Where a supply is required to a new development within an
    property deeds include:                           existing urban area or other area where there is no existing, or
                                                      space for a new, transformer sub-station nearby then it will be
                                                      necessary for the development to make an accessible room
    • Details of electricity poles                    available for the installation of a transformer.
      and street lights located
      within or around the                     Possible Arrangement of Services
                                                      A separate Technical Sheet: Combined Utility Services
    • Notice to plot purchasers                       Summary plans provide indicative groupings for
      advising of CEB’s statutory                     arrangements of the various utilities that generally need to
      authority to lop or fell                        be laid within the road and utility reserve. These drawings
      trees to maintain safe                          are for information only and are not intended to cover every
      clearances                                      eventuality. They do, however, serve to demonstrate why it
                                                      is important to consider all the utilities and how they relate to
                                                      each other when preparing development plans.

                                               Further Advice and Information
      Property developers should
                                                      For further advice and information please contact:
       require plot purchasers to
     keep all utility/road reserves
      free of structures, trees and                   Senior Planning Engineer
        other vegetation. Access                      Loreto Convent Street
      for maintenance and other                       Curepipe
     purposes must be possible at
                                                      Tel No. 670 6040 / 674 0551
                 all times.
                                                      Fax No. 674 0445

Ministry of Housing and Lands, November 2004

Shared By: