ENA ER S5-1 : ISSUE 1 AMD 2 1970

Applies to fixed earthing installations for all substations. This wide coverage requires that all size references in the document must be related to the whole range of substations; further, because substation circumstances vary widely, it is not possible to define in voltages terms like "large", "very small", etc. These must be interpreted according to the context. In large substations the designer will often have to provide for a large earth fault current as well as a large area, thus requiring an extensive installation. In other substations little may be required if, for example, the earth fault current is relatively small and the substation serves any underground cable network which itself affords a low impedance connection with the earth. While the theoretical considerations apply to all substations, in practice much of this document relates mainly to large substations.