UK TT undetectable PEN fault

<div class="bbWrapper"><blockquote data-attributes="member: 149787" data-quote="Tom256" data-source="post: 1878583" class="bbCodeBlock bbCodeBlock--expandable bbCodeBlock--quote js-expandWatch"> <div class="bbCodeBlock-title"> <a href="/goto/post?id=1878583" class="bbCodeBlock-sourceJump" rel="nofollow" data-xf-click="attribution" data-content-selector="#post-1878583">Tom256 said:</a> </div> <div class="bbCodeBlock-content"> <div class="bbCodeBlock-expandContent js-expandContent "> The requirement was for a TT system but is that now what you have? What earthing system do you now have? Is the intended installation earthing now compliant ? </div> <div class="bbCodeBlock-expandLink js-expandLink"><a role="button" tabindex="0">Click to expand...</a></div> </div> </blockquote>Ah right it’s now inadvertently a TN-C-S and where there is no predictable path for current to take.<br /> Current can travel down into the source earth, the installation earth, back somewhere in the house, somewhere completely different than the house if that thing is somehow connected to something conductive in the house, or some combination of all the above.</div>

<div class="bbWrapper"><blockquote data-attributes="member: 175737" data-quote="Hakuhou" data-source="post: 1878620" class="bbCodeBlock bbCodeBlock--expandable bbCodeBlock--quote js-expandWatch"> <div class="bbCodeBlock-title"> <a href="/goto/post?id=1878620" class="bbCodeBlock-sourceJump" rel="nofollow" data-xf-click="attribution" data-content-selector="#post-1878620">Hakuhou said:</a> </div> <div class="bbCodeBlock-content"> <div class="bbCodeBlock-expandContent js-expandContent "> Ah right it’s now inadvertently a TN-C-S.<br /> I would say no, since a fault can either travel down into the source earth, the installation earth, back somewhere in the house, somewhere completely different than the house if that thing is somehow connected to something conductive in the house, or some combination of all the above.<br /> Given the goal of an earthing system is to predictably direct a fault this installation would not be compliant. </div> <div class="bbCodeBlock-expandLink js-expandLink"><a role="button" tabindex="0">Click to expand...</a></div> </div> </blockquote>As already said the Earth rod is connected before the Consumer unit so all the rod is doing is adding to the PME earthing.<br /> <br /> If the Rod was connected to the earth bar in the Consumer unit and penetrated the Neutral, it would no longer be a TNC-S as there would be no Separation from the earth bar.</div>

<div class="bbWrapper"><blockquote data-attributes="member: 175737" data-quote="Hakuhou" data-source="post: 1878620" class="bbCodeBlock bbCodeBlock--expandable bbCodeBlock--quote js-expandWatch"> <div class="bbCodeBlock-title"> <a href="/goto/post?id=1878620" class="bbCodeBlock-sourceJump" rel="nofollow" data-xf-click="attribution" data-content-selector="#post-1878620">Hakuhou said:</a> </div> <div class="bbCodeBlock-content"> <div class="bbCodeBlock-expandContent js-expandContent "> where there is no predictable path for current to take.<br /> Current </div> <div class="bbCodeBlock-expandLink js-expandLink"><a role="button" tabindex="0">Click to expand...</a></div> </div> </blockquote>Unless the CNE conductors are completed severed, current will always take the path of least resistance which is most unlikely to be your new earth rod.</div>

<div class="bbWrapper"><blockquote data-attributes="member: 112973" data-quote="DefyG" data-source="post: 1878622" class="bbCodeBlock bbCodeBlock--expandable bbCodeBlock--quote js-expandWatch"> <div class="bbCodeBlock-title"> <a href="/goto/post?id=1878622" class="bbCodeBlock-sourceJump" rel="nofollow" data-xf-click="attribution" data-content-selector="#post-1878622">DefyG said:</a> </div> <div class="bbCodeBlock-content"> <div class="bbCodeBlock-expandContent js-expandContent "> Unless the CNE conductors are completed severed, current will always take the path of least resistance which is most unlikely to be your new earth rod. </div> <div class="bbCodeBlock-expandLink js-expandLink"><a role="button" tabindex="0">Click to expand...</a></div> </div> </blockquote>Current flows through all paths in an amount inversely proportional to their resistance. <img src="https://cdn.jsdelivr.net/gh/twitter/[email protected]/assets/72x72/1f642.png" class="smilie smilie--emoji" loading="lazy" width="72" height="72" alt=":)" title="Smile :)" data-smilie="1"data-shortname=":)" /></div>

<div class="bbWrapper"><blockquote data-attributes="member: 143657" data-quote="mainline" data-source="post: 1878626" class="bbCodeBlock bbCodeBlock--expandable bbCodeBlock--quote js-expandWatch"> <div class="bbCodeBlock-title"> <a href="/goto/post?id=1878626" class="bbCodeBlock-sourceJump" rel="nofollow" data-xf-click="attribution" data-content-selector="#post-1878626">mainline said:</a> </div> <div class="bbCodeBlock-content"> <div class="bbCodeBlock-expandContent js-expandContent "> Current flows through all paths in an amount inversely proportional to their resistance. <img src="https://cdn.jsdelivr.net/gh/twitter/[email protected]/assets/72x72/1f642.png" class="smilie smilie--emoji" loading="lazy" width="72" height="72" alt=":)" title="Smile :)" data-smilie="1"data-shortname=":)" /> </div> <div class="bbCodeBlock-expandLink js-expandLink"><a role="button" tabindex="0">Click to expand...</a></div> </div> </blockquote>Is this the point now reached where we move on to touch voltages? Because if we do I need a coffee first... with some bacon to dunk into it</div>

<div class="bbWrapper"><blockquote data-attributes="member: 143657" data-quote="mainline" data-source="post: 1878621" class="bbCodeBlock bbCodeBlock--expandable bbCodeBlock--quote js-expandWatch"> <div class="bbCodeBlock-title"> <a href="/goto/post?id=1878621" class="bbCodeBlock-sourceJump" rel="nofollow" data-xf-click="attribution" data-content-selector="#post-1878621">mainline said:</a> </div> <div class="bbCodeBlock-content"> <div class="bbCodeBlock-expandContent js-expandContent "> As already said the Earth rod is connected before the Consumer unit so all the rod is doing is adding to the PME earthing.<br /> <br /> If the Rod was connected to the earth bar in the Consumer unit and penetrated the Neutral, it would no longer be a TNC-S as there would be no Separation from the earth bar. </div> <div class="bbCodeBlock-expandLink js-expandLink"><a role="button" tabindex="0">Click to expand...</a></div> </div> </blockquote>Thank you, getting there.<br /> So this is a TN-S system but where the installation’s earth has been connected to the “first” earth in the PME chain.<br /> <br /> <script class="js-extraPhrases" type="application/json"> { "lightbox_close": "Close", "lightbox_next": "Next", "lightbox_previous": "Previous", "lightbox_error": "The requested content cannot be loaded. Please try again later.", "lightbox_start_slideshow": "Start slideshow", "lightbox_stop_slideshow": "Stop slideshow", "lightbox_full_screen": "Full screen", "lightbox_thumbnails": "Thumbnails", "lightbox_download": "Download", "lightbox_share": "Share", "lightbox_zoom": "Zoom", "lightbox_new_window": "New window", "lightbox_toggle_sidebar": "Toggle sidebar" } </script> <a href="https://www.electriciansforums.net/attachments/img_2857-jpeg.119470/" target="_blank" class="js-lbImage" data-lb-sidebar-href="" data-lb-caption-extra-html=""><img src="https://electricians.s3.eu-west-1.amazonaws.com/data/attachments/78/78869-8a2a62c4d197f852ef02742004f859ed.jpg?hash=iipixNGX-F" class="bbImage " style="" alt="IMG_2857.jpeg" title="IMG_2857.jpeg" width="1029" height="550" loading="lazy" /></a></div>

<div class="bbWrapper"><blockquote data-attributes="member: 112973" data-quote="DefyG" data-source="post: 1878622" class="bbCodeBlock bbCodeBlock--expandable bbCodeBlock--quote js-expandWatch"> <div class="bbCodeBlock-title"> <a href="/goto/post?id=1878622" class="bbCodeBlock-sourceJump" rel="nofollow" data-xf-click="attribution" data-content-selector="#post-1878622">DefyG said:</a> </div> <div class="bbCodeBlock-content"> <div class="bbCodeBlock-expandContent js-expandContent "> current will always take the path of least resistance which is most unlikely to be your new earth rod. </div> <div class="bbCodeBlock-expandLink js-expandLink"><a role="button" tabindex="0">Click to expand...</a></div> </div> </blockquote>Probably should have said &#039;most&#039; as the earth rod having a significantly higher resistance, the current would be insignificant (probably) but this is all hyperthetical!</div>

<div class="bbWrapper"><blockquote data-attributes="member: 175737" data-quote="Hakuhou" data-source="post: 1878628" class="bbCodeBlock bbCodeBlock--expandable bbCodeBlock--quote js-expandWatch"> <div class="bbCodeBlock-title"> <a href="/goto/post?id=1878628" class="bbCodeBlock-sourceJump" rel="nofollow" data-xf-click="attribution" data-content-selector="#post-1878628">Hakuhou said:</a> </div> <div class="bbCodeBlock-content"> <div class="bbCodeBlock-expandContent js-expandContent "> Thank you, getting there.<br /> So this is a TN-S system but where the installation’s earth has been connected to the “first” earth in the PME chain.<br /> <br /> <a href="https://www.electriciansforums.net/attachments/119470/" target="_blank">View attachment 119470</a> </div> <div class="bbCodeBlock-expandLink js-expandLink"><a role="button" tabindex="0">Click to expand...</a></div> </div> </blockquote>That is not TN-S. Do you understand why?</div>

<div class="bbWrapper"><blockquote data-attributes="member: 143657" data-quote="mainline" data-source="post: 1878626" class="bbCodeBlock bbCodeBlock--expandable bbCodeBlock--quote js-expandWatch"> <div class="bbCodeBlock-title"> <a href="/goto/post?id=1878626" class="bbCodeBlock-sourceJump" rel="nofollow" data-xf-click="attribution" data-content-selector="#post-1878626">mainline said:</a> </div> <div class="bbCodeBlock-content"> <div class="bbCodeBlock-expandContent js-expandContent "> Current flows through all paths in an amount inversely proportional to their resistance. <img src="https://cdn.jsdelivr.net/gh/twitter/[email protected]/assets/72x72/1f642.png" class="smilie smilie--emoji" loading="lazy" width="72" height="72" alt=":)" title="Smile :)" data-smilie="1"data-shortname=":)" /> </div> <div class="bbCodeBlock-expandLink js-expandLink"><a role="button" tabindex="0">Click to expand...</a></div> </div> </blockquote>Ohm’s law right? V=I/R</div>

<div class="bbWrapper"><blockquote data-attributes="member: 175737" data-quote="Hakuhou" data-source="post: 1878631" class="bbCodeBlock bbCodeBlock--expandable bbCodeBlock--quote js-expandWatch"> <div class="bbCodeBlock-title"> <a href="/goto/post?id=1878631" class="bbCodeBlock-sourceJump" rel="nofollow" data-xf-click="attribution" data-content-selector="#post-1878631">Hakuhou said:</a> </div> <div class="bbCodeBlock-content"> <div class="bbCodeBlock-expandContent js-expandContent "> Ohm’s law right? V=I/R </div> <div class="bbCodeBlock-expandLink js-expandLink"><a role="button" tabindex="0">Click to expand...</a></div> </div> </blockquote>Wrong</div>

<div class="bbWrapper"><blockquote data-attributes="member: 149787" data-quote="Tom256" data-source="post: 1878630" class="bbCodeBlock bbCodeBlock--expandable bbCodeBlock--quote js-expandWatch"> <div class="bbCodeBlock-title"> <a href="/goto/post?id=1878630" class="bbCodeBlock-sourceJump" rel="nofollow" data-xf-click="attribution" data-content-selector="#post-1878630">Tom256 said:</a> </div> <div class="bbCodeBlock-content"> <div class="bbCodeBlock-expandContent js-expandContent "> That is not TN-S. Do you understand why? </div> <div class="bbCodeBlock-expandLink js-expandLink"><a role="button" tabindex="0">Click to expand...</a></div> </div> </blockquote>Hmm, for TN-S the installation earth is directly connected to the source earth (usually via the DNO’s supply cable’s metal sheath, this is not the case so not TN-S.<br /> For TN-C-S the separate bit is missing <br /> So yes not TN-S, but not TN-C-S since the S is missing.<br /> By process of elimination it’s a TN-C, in the book I read.<br /> “TN-C is not generally permitted in the UK.”<br /> Ok time to read up on TN-C.</div>

<div class="bbWrapper"><blockquote data-attributes="member: 112973" data-quote="DefyG" data-source="post: 1878632" class="bbCodeBlock bbCodeBlock--expandable bbCodeBlock--quote js-expandWatch"> <div class="bbCodeBlock-title"> <a href="/goto/post?id=1878632" class="bbCodeBlock-sourceJump" rel="nofollow" data-xf-click="attribution" data-content-selector="#post-1878632">DefyG said:</a> </div> <div class="bbCodeBlock-content"> <div class="bbCodeBlock-expandContent js-expandContent "> Wrong </div> <div class="bbCodeBlock-expandLink js-expandLink"><a role="button" tabindex="0">Click to expand...</a></div> </div> </blockquote>Typo V=IR -&gt; I=V/R</div>

<div class="bbWrapper"><blockquote data-attributes="member: 175737" data-quote="Hakuhou" data-source="post: 1878633" class="bbCodeBlock bbCodeBlock--expandable bbCodeBlock--quote js-expandWatch"> <div class="bbCodeBlock-title"> <a href="/goto/post?id=1878633" class="bbCodeBlock-sourceJump" rel="nofollow" data-xf-click="attribution" data-content-selector="#post-1878633">Hakuhou said:</a> </div> <div class="bbCodeBlock-content"> <div class="bbCodeBlock-expandContent js-expandContent "> Hmm, for TN-S the installation earth is directly connected to the source earth (usually via the DNO’s supply cable’s metal sheath, this is not the case so not TN-S.<br /> For TN-C-S the separate bit is missing<br /> So yes not TN-S, but not TN-C-S since the S is missing.<br /> By process of elimination it’s a TN-C, in the book I read.<br /> “TN-C is not generally permitted in the UK.”<br /> Ok time to read up on TN-C. </div> <div class="bbCodeBlock-expandLink js-expandLink"><a role="button" tabindex="0">Click to expand...</a></div> </div> </blockquote>Consider the &#039;S&#039; in TN-C-S. What part of the electrical system does this aspect apply to? Where do the neutral and the protective earth become separated never again to come together?</div>

<div class="bbWrapper"><blockquote data-attributes="member: 149787" data-quote="Tom256" data-source="post: 1878637" class="bbCodeBlock bbCodeBlock--expandable bbCodeBlock--quote js-expandWatch"> <div class="bbCodeBlock-title"> <a href="/goto/post?id=1878637" class="bbCodeBlock-sourceJump" rel="nofollow" data-xf-click="attribution" data-content-selector="#post-1878637">Tom256 said:</a> </div> <div class="bbCodeBlock-content"> <div class="bbCodeBlock-expandContent js-expandContent "> Consider the &#039;S&#039; in TN-C-S. What part of the electrical system does this aspect apply to? Where do the neutral and the protective earth become separated never again to come together? </div> <div class="bbCodeBlock-expandLink js-expandLink"><a role="button" tabindex="0">Click to expand...</a></div> </div> </blockquote>To help with your consideration of this. Using your diagram in post #21.<br /> The earth point on that 3rd electrode (closest to the installation) was moved along by some form of pixie a tad and was now at the origin of the customers installation.</div>

<div class="bbWrapper"><blockquote data-attributes="member: 175737" data-quote="Hakuhou" data-source="post: 1878633" class="bbCodeBlock bbCodeBlock--expandable bbCodeBlock--quote js-expandWatch"> <div class="bbCodeBlock-title"> <a href="/goto/post?id=1878633" class="bbCodeBlock-sourceJump" rel="nofollow" data-xf-click="attribution" data-content-selector="#post-1878633">Hakuhou said:</a> </div> <div class="bbCodeBlock-content"> <div class="bbCodeBlock-expandContent js-expandContent "> Hmm, for TN-S the installation earth is directly connected to the source earth (usually via the DNO’s supply cable’s metal sheath, this is not the case so not TN-S.<br /> For TN-C-S the separate bit is missing<br /> So yes not TN-S, but not TN-C-S since the S is missing.<br /> By process of elimination it’s a TN-C, in the book I read.<br /> “TN-C is not generally permitted in the UK.”<br /> Ok time to read up on TN-C. </div> <div class="bbCodeBlock-expandLink js-expandLink"><a role="button" tabindex="0">Click to expand...</a></div> </div> </blockquote><br /> For it to be TT earthing, you would have to have the ROD connected to the earth bar in the consumer unit.<br /> <br /> The PEN would be isolated from that consumer unit.</div>