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Do-It-Yourself (DIY) Question & Answer Forum
TN-C-S Pitfalls
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<blockquote data-quote="ProDave" data-source="post: 251559" data-attributes="member: 6969"><p>Good points steps.</p><p></p><p>The more I read about PME, the more I realise it's a flawed system. NOT because in principle it's flawed, but because the DNO's persist in using concentric cable which is seriously flawed.</p><p></p><p>As for DNO's splicing in sections of concentric into a TNS supply, show me where in the regs it allows for a supply type that starts it's journey as TNS, has a mid section of TNCS spliced in, then it's back to TNS for delivery to the customer. What gives the DNO authority to ignore 7671 and devise such a non standard, non recognised earthing system?</p><p></p><p>The other thing that bugs me, up here in the sticks, I've seen several installs where a single property is fed from an overhead transformer on a pole. It's usual to dig a trench in two directions. Away from the property they bury an HV earth, then towards the property (usually the same trench carrying the customers concentric supply cable) they bury an LV earth.</p><p></p><p>So that's a TNCS supply courtesy of the combined earth and neutral conductor from the transformer to the customer.</p><p></p><p>But HOW does it qualify as PME. Please tell me where the MULTIPLE earth's are (I can only count one)? But they still stick a PME label on the supply head.</p></blockquote><p></p>
[QUOTE="ProDave, post: 251559, member: 6969"] Good points steps. The more I read about PME, the more I realise it's a flawed system. NOT because in principle it's flawed, but because the DNO's persist in using concentric cable which is seriously flawed. As for DNO's splicing in sections of concentric into a TNS supply, show me where in the regs it allows for a supply type that starts it's journey as TNS, has a mid section of TNCS spliced in, then it's back to TNS for delivery to the customer. What gives the DNO authority to ignore 7671 and devise such a non standard, non recognised earthing system? The other thing that bugs me, up here in the sticks, I've seen several installs where a single property is fed from an overhead transformer on a pole. It's usual to dig a trench in two directions. Away from the property they bury an HV earth, then towards the property (usually the same trench carrying the customers concentric supply cable) they bury an LV earth. So that's a TNCS supply courtesy of the combined earth and neutral conductor from the transformer to the customer. But HOW does it qualify as PME. Please tell me where the MULTIPLE earth's are (I can only count one)? But they still stick a PME label on the supply head. [/QUOTE]
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