PURPOSE AND SCOPE

Earthing systems are installed to protect life and assets from the potentially damaging effects of 50Hz faults (short circuits) or transient phenomena such as lightning and switching operations. Such systems typically comprise a below ground grid of bare copper conductors laid horizontally at a shallow depth – sometimes supplemented via connections to vertical earthing rods driven to greater depth – plus a series of above ground conductors that facilitate the connection of specific equipment to the below ground system. Earthing systems shall be managed as an ‘underground service' in accordance with HSG47 ‘Avoiding Danger from Underground Services'.

This procedure defines the management of documentation associated with Substation and Overhead Line Earthing systems. The earthing process with respect to roles, along the phase of investment plan, is tabulated in Appendix A. Appendix B illustrates the earthing design flow chart.

This procedure applies to all projects which comprise the UK Transmission Construction Electricity Capital Programme, including associated revenue projects.

Technical and Design issues relating to Substation earthing are contained in TS 3.1.2. Overhead line earthing is covered by both TS 3.1.2 and TGN(E) 199. Routine Maintenance of the Substation earthing is covered by the existing Asset Management procedures.