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The maximum permissible disconnection time is 0.4 s in TN system. Why and from where this value (0.4 s) is obtained?
Former Community Member
The maximum permissible disconnection time in in the event of a short circuit between a phase conductor and a body or protective conductor or a protective-neutral conductor is 0.4 s in TN system. Does anybody know this value (0.4 s) obtains from where? How this value is obtained?
Presumably distribution circuits are allowed to have long disconnect times because they don't expect anyone to actually come into live contact with them very often (apart from the occasional shortly-to-be-deceased sparky fiddling about inside a DB). All the nasty end-user paraphernalia like water heaters, power tools etc are connected further downstream with 0.2/0.4s disconnect times.
Presumably distribution circuits are allowed to have long disconnect times because they don't expect anyone to actually come into live contact with them very often (apart from the occasional shortly-to-be-deceased sparky fiddling about inside a DB). All the nasty end-user paraphernalia like water heaters, power tools etc are connected further downstream with 0.2/0.4s disconnect times.
