Paul Meenan CEng FIET from e5 discusses a common, emerging issue that can be confusing for industry professionals. It all started in early 2019, with a report of some form of arcing/sparks seen on a main ground terminal/rod when a new hitch connector was attached to it. I know what you’re thinking: “What could be the reason for that?” It can’t be an earth leak, it’s a dead (or inactive) conductor; It is a safety cable, in its simplest form, the grounding exists only to connect parts of the electrical installation to the general mass of earth … and: a) ensure the separation of protective devices, b) ensure that all conductive parts are connected to each other, so that they remain at the same potential under error conditions. Besides, this is a hitch connector, so what’s going on? Our clamp and “Lo and behold” meter outputs 43.4 amps! Fault finding What causes unusual amounts of power to appear on a conductor designed only to carry voltage/current under fault conditions? We are now on the task of finding the error. The quickest way was to connect to the DNO and take out the fuse after the installation was completely de-energized however we still found large amounts of current flowing. Here comes the strange part. The Electrical in Action Regulations 1989 (a book that has not been visited enough, and some have almost forgotten that it exists) states that electrical insulation is: 12.–(2) “Insulation” means disconnecting and disconnecting electrical equipment from every source of electrical power in such a way that it is This separation and separation is safe. So, how do you do it safely when this happens? To answer this question, we need to explore a well-known phenomenon of network operators of supplies (DNO or DSO). We may have heard it called a broken PEN (protective earth neutral) or lost PEN or DNC (transformed neutral). We’ve worked with Tangle Tamers, an independent grounding consulting firm, and have dedicated a significant amount of time to investigating and understanding what is happening and why this is happening. Fortunately, IET has now acknowledged this in its post, Wiring Matters March 2021. You can now sum it up by looking at the image at the top of the page, which shows a cut of two cables. The left is the CNE type, in which the neutral and ground are combined. It is also known as the PEN conductor used in the supply of TN-CS. The cable on the right is known as SNE (Separate Neutral and Earth), which is also what we class as a TN-S supply cable. Now in theory, DNOs shouldn’t mix cables, but that’s where the problem lies – they do! The cables pictured were wired together when the old PILC-coated SNE cable was repaired underground with a CNE cable – the one on the left of the picture to be exact! This immediately connects NE. So what on visual inspection looks like a TN-S is actually a TN-CS. The frustrating part is that the network operator did nothing, and the DNO did nothing inside the installation to inform the installation owner or electrician(s). Furthermore, research inquiries were made and an email was made to the DNO and the response responded that it would be prudent to assume that most of the supplies are now connected or diverted on the street to TN-CS – except for TN-S supplies that are still around but likely only on private networks. Note, I don’t call it TN-CS PME! PME (Protective Multiple Earthing) describes the multiple rails or ground connection that a cable must have. However, I don’t think many old transformer cables, even at the splices, are wired to an electrode. However, we have the usual diagrams of a grounding system showing the different grounding systems – TN-S, TN-CS and TT – but in fact we may find hybrid types of these systems. Which raises another argument: do we need to re-evaluate and revise the problem that grounding systems have changed over time and become hybrids of those recognized? How do we handle DNO safely? Going forward, it may be helpful for electricians to familiarize themselves with the MOCOPA manual as an addition to your CPD, put the 105 in your phone and learn about the DNO engineers. Also, I recommend that you start checking grounding systems with clamp gauges to protect yourself. Unfortunately, our industry appears to be lagging behind in energy management when it comes to safe work operations. Just look at arc flash as another example. Do you want more information? Tangle Tamers, along with the e5 team, have produced a more in-depth guide available for viewing online. It explains what to look for and how to test for the presence of a DNC. Years of research have gone into the manual, and it seems clear that electricians will have to start checking as part of a safe insulation procedure for not only the presence of voltage, but also current. View the full guide by clicking here. All photos courtesy of Paul Minnan
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