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Just Moved And Learned What A Tt Earth Is, Some Questions!
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<blockquote data-quote="Doc Hudson" data-source="post: 403708" data-attributes="member: 1607"><p>There are tables in the regulations that give the resistance values of standard copper conductors. (2.5mm2 is 7.41miliohms per metre 16.0mm2 is 1.15miliohms per meter)</p><p></p><p>so if you compare 2.5mm2 &amp; 16mm2 CSA you are talking of a difference of something around 0.062ohms per 10m length. So even with a long run from your CU to the rod the difference in actual resistance value will have negligible effect upon the overall earth loop impedance path back via the rod. The Ra of the rod itself will be the biggest governing factor. Unless you are getting your rod down below 10ohms the fault current via a direct short Live to Earth is not going to be a major issue for a piece of 2.5mm2 CSA. and assuming your RCD is operating correctly then the power will be disconnected in a very short time well before the earth has to carry much current. There may be some other factors that require increased CSA and mechanical protection to the cable, but a TT does not need a 16mm earth by default. It would be interesting to know the reasons why your electrician recommends 16.0mm2</p><p></p><p>Doc H.</p></blockquote><p></p>
[QUOTE="Doc Hudson, post: 403708, member: 1607"] There are tables in the regulations that give the resistance values of standard copper conductors. (2.5mm2 is 7.41miliohms per metre 16.0mm2 is 1.15miliohms per meter) so if you compare 2.5mm2 & 16mm2 CSA you are talking of a difference of something around 0.062ohms per 10m length. So even with a long run from your CU to the rod the difference in actual resistance value will have negligible effect upon the overall earth loop impedance path back via the rod. The Ra of the rod itself will be the biggest governing factor. Unless you are getting your rod down below 10ohms the fault current via a direct short Live to Earth is not going to be a major issue for a piece of 2.5mm2 CSA. and assuming your RCD is operating correctly then the power will be disconnected in a very short time well before the earth has to carry much current. There may be some other factors that require increased CSA and mechanical protection to the cable, but a TT does not need a 16mm earth by default. It would be interesting to know the reasons why your electrician recommends 16.0mm2 Doc H. [/QUOTE]
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Just Moved And Learned What A Tt Earth Is, Some Questions!
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