scope:

PURPOSE AND SCOPE

This document defines the functional performance and test requirements for earthing systems forming part of the National Grid System and protected by fast acting protection systems *. It supports the more general conditions defined in the companion documents TS 1 and TS 2.1.

The requirements of this document shall apply to new substations, cable sealing end and tower constructions and where reasonably practicable to extensions or modifications of existing substations and cable sealing ends and tower refurbishment.

Where a substation, cable sealing end or tower is being extended or modified, National Grid will state if it is necessary to control the earth potential rise (EPR) in accordance with 1.2. If not stated, this requirement does not need to be applied.

*Note: Fast acting protection systems are those designed to achieve a target total fault clearance time of less than 200ms.