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Do-It-Yourself (DIY) Question & Answer Forum
Max Zs
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<blockquote data-quote="professional" data-source="post: 23947" data-attributes="member: 1381"><p>I think that the one thing that is being forgotten in this `debate` is the fundamental differences in protection on TT and TNS/TNCS systems. The reason why the max tabulated (or 80%) values on a TNS/TNCS system must still be adhered to <strong>wherever possible</strong> is that the possibility of the rcd failing has to be taken into account. Clearly on a TT system there is no external `earth` to back up the rod but the regs are merely ensuring that the installer is making best use of the earthing arrangements available under the relevant circumstances. Surely, if an external earth of low impedance is available then it makes sense to make use of it in the event of a problem occurring with the installation?</p><p></p><p>Remember, the regs are guidlines to best practice with regard to safety - not an instruction manual for installers.</p></blockquote><p></p>
[QUOTE="professional, post: 23947, member: 1381"] I think that the one thing that is being forgotten in this `debate` is the fundamental differences in protection on TT and TNS/TNCS systems. The reason why the max tabulated (or 80%) values on a TNS/TNCS system must still be adhered to [B]wherever possible[/B] is that the possibility of the rcd failing has to be taken into account. Clearly on a TT system there is no external `earth` to back up the rod but the regs are merely ensuring that the installer is making best use of the earthing arrangements available under the relevant circumstances. Surely, if an external earth of low impedance is available then it makes sense to make use of it in the event of a problem occurring with the installation? Remember, the regs are guidlines to best practice with regard to safety - not an instruction manual for installers. [/QUOTE]
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