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Student & Learning Zone - City & Guilds
How Fast Should A Fuse Trip If Cannot Let Go?
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<blockquote data-quote="msb2003" data-source="post: 324222" data-attributes="member: 3816"><p>The regulations do specify 0.4 sec and 5 sec respectively, for TN systems and 0.2 and 1 sec for TT systems (don`t forget distribution circuits are the same as circuits &gt;32A) however your comment I`ve highlighted that they will always disconnect in these times is incorrect. These are the maximum times permitted and they will only be achieved if your Zs values are complient with the values given (use the OSG values as the Regs values must have the rule of thumb applied and multiplied by 0.8).</p><p></p><p>If you cannot achieve the required Zs values, an RCD can be used</p></blockquote><p></p>
[QUOTE="msb2003, post: 324222, member: 3816"] The regulations do specify 0.4 sec and 5 sec respectively, for TN systems and 0.2 and 1 sec for TT systems (don`t forget distribution circuits are the same as circuits >32A) however your comment I`ve highlighted that they will always disconnect in these times is incorrect. These are the maximum times permitted and they will only be achieved if your Zs values are complient with the values given (use the OSG values as the Regs values must have the rule of thumb applied and multiplied by 0.8). If you cannot achieve the required Zs values, an RCD can be used [/QUOTE]
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Student & Learning Zone - City & Guilds
How Fast Should A Fuse Trip If Cannot Let Go?
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