scope:

PURPOSE AND SCOPE

This policy defines the requirements for disconnectors and earth switches which, due to features of their design, cannot be operated as independent devices. In particular it addresses the potential incompatibility of these device combinations with the National Grid Transco (NGT) Safety Rules requirement to lock "points of isolation" prior to operation of any associated earth switch. Whilst this policy has been prompted by recent designs of 145kV GIS equipment the requirements contained herein are applicable across all voltage ranges & technologies. The policy applies to applications which form part of, or affect the integrity of, the NGT (Electricity) system.