A power limit concept is described for the assessment and, where necessary, testing of multi-way junction and marshalling boxes protected by any of the established protection concepts. The power limit concept results in severe limitation of the maximum permissible numbers of terminal ways compared with earlier methods of safety assessment, because it must be assumed that terminals will be operated at their maximum ratings. Where terminals are operated below their ratings, and where diversity applies, significant relaxations can be achieved which the concept allows to be calculated. Appropriate guidance on achieving these relaxations should be given in future codes of practice.
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