Changes to Part Three were also kept to a minimum because a new version of the International document upon which it is based will be published shortly after the cut-off date for 18th Edition work.
The reintroduction of Chapter 46 giving requirements for isolation and switching is acknowledged in Regulations 301.1 (Assessment of general characteristics) and 314.3 (Division of installation).
The following text which used to appear below Fig 3.9 (TN-C-S (PME) system) has been deleted:
The usual form of a TN-C-S system is as shown, where the supply is TN-C and the arrangement in the installations is TN-S.
An electrical system, as defined, consists of one or more sources of supply and an installation. An installation therefore forms part of a system but, in the context of Fig 3.9, an installation does not contain several systems.
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