The low voltage distribution systems are designed as radial networks from individual distribution substations. At the design stage consideration is given to the ability of the network to supply identified future development. Radial systems that do not, and are not planned to, interconnect with adjacent substations are designed using tapered mains.
The existing LV systems comprise mainly underground cables in urban or dense development areas and overhead lines in rural areas. In some areas 3-phase supply is not available and, in many rural locations replacement of the HV/LV distribution transformer may be required to achieve 3 phase user connection.
There is a significant variety of both cable construction and sizes in use on the underground systems.
On existing LV overhead systems a variety of conductor sizes is used and supports are predominately wood pole. Whilst the majority of legacy overhead systems are bare conductor, EDF Energy Networks (SPN) plc is undertaking a programme of replacement of these with bundled aerial insulated conductor on a prioritised basis of condition monitoring and public safety risk.
The LV systems provide PME/PNB earthing facilities for user connection – subject to the appropriate bonding and terminal equipment being provided by the user.
In many rural areas there is no local LV distribution system and individual user properties may have dedicated HV/LV substations. Whilst this is predominately in areas where the HV system is overhead the 3.5kV and 2kV underground systems are also generally configured in this way with individual compact substations at each property. In particular where 2kV systems are in use three-phase connection may be impracticable as the cost of connection may include substantial HV works.
