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THE CAMPAIGN FOR REAL EARTHING

John Peckham
I think that we were considering adopting PME earthing systems today on what we know now we would say no thanks?


I strongly believe that the use of PME earthing systems is inherently unsafe. I am keen to hear any technical arguments to defend the use of PME?


Most PME DNO new distribution cable use 3 core Wavecon cables for UG distribution with single phase concentric cables tapped off for single phase users. For overhead open wire supplies of newer installs ABC cable.


There is no reason not to use 4 core Wavecons and distribute a much safer TN-S earthing system other than the cables will be a 1/3rd more expensive.


 I believe that the DNOs having been tentatively asking government  for a £trillion pounds to upgrade their networks for when we stop burning fossil fuels and go all electric. No doubt the DNOs hope that the government, civil servants and politicians will have forgotten that these private companies purchased a public assets for a knock down price with the idea that the public would no longer have to subsidies a public body! 


A good start would be that no new supplies will be PME, no replacement cables will be PME and no repairs to cables will be PME conversions. For instance a new housing estate would have to be an all TN-S installation. I understand that WPD are already installing TN-S earthing systems for new housing estates. If this is the case then well done WPD. Can anyone confirm this?


I am also concerned about the degradation of the of the Global Earthing System with use of all plastic covered cables, no bonding to metallic service pipes and the failure on DNO contractors to install earth rods and joints to save time and money. Will we start to see 442 type over voltages?


Look at my EV charging thread and the measures we are having to deploy due to PME earthing, we are having to do this because the PME system is inherently unsafe!


Is there support for my proposed campaign?
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    Brazil:  I didn't know that - thanks .. will ask someone I know from there. Perhaps they use TT for the LV side, or just have very reliable soil.  LV lines can be be hundreds of metres in some places, so even by themselves the lightning pickup isn't to be ignored. 

    Yes, systems where earth-currents are expected in normal operation remove some important possibilities for fault detection. At medium-voltage (or high-voltage as UK DNOs and IEC would say - excuse me that I've become used to this 'MV' description) it's not just SWER systems with this problem, but also the system used in most of the US states and some places beyond, which is basically 'MEN' on the 13.8 kV system along with bonding to the LV neutrals. Then some people complain about things like induced currents in pipelines, partly due to currents in 13.8 kV lines not balancing. And also about corroded neutrals on 13.8 kV cables causing shock danger. Its main benefits, as at LV, are that simple overcurrent protection can provide selective protection of the many branches and transformers that are needed when using a lower low-voltage distribution in spite of heavy loads and big spaces between homes.  In contrast, in Sweden most MV lines (unless metal cased) have to detect and promptly disconnect for an earth fault below about 5 kohm, i.e. about 1 A (they're usually resonant-earthed, so noticing a fault isn't that hard, even if locating is).


    Following from some earlier points, I agree that regardless of the continued use of 'PME' or a separate protective conductor, monitoring should (and eventually will) start to get some serious use.  There's no real technical barrier to it even now, and there are already smart meters in some countries that report strange voltages that could indicate a neutral problem. Much more can be done, including the use of multiple measurements together. But various issues of tradition, poor communication channels, no low-price products being pushed hard, not huge gains (serious accidents seldom, serious damages awarded even more seldom) limit the speed of uptake.

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    Brazil:  I didn't know that - thanks .. will ask someone I know from there. Perhaps they use TT for the LV side, or just have very reliable soil.  LV lines can be be hundreds of metres in some places, so even by themselves the lightning pickup isn't to be ignored. 

    Yes, systems where earth-currents are expected in normal operation remove some important possibilities for fault detection. At medium-voltage (or high-voltage as UK DNOs and IEC would say - excuse me that I've become used to this 'MV' description) it's not just SWER systems with this problem, but also the system used in most of the US states and some places beyond, which is basically 'MEN' on the 13.8 kV system along with bonding to the LV neutrals. Then some people complain about things like induced currents in pipelines, partly due to currents in 13.8 kV lines not balancing. And also about corroded neutrals on 13.8 kV cables causing shock danger. Its main benefits, as at LV, are that simple overcurrent protection can provide selective protection of the many branches and transformers that are needed when using a lower low-voltage distribution in spite of heavy loads and big spaces between homes.  In contrast, in Sweden most MV lines (unless metal cased) have to detect and promptly disconnect for an earth fault below about 5 kohm, i.e. about 1 A (they're usually resonant-earthed, so noticing a fault isn't that hard, even if locating is).


    Following from some earlier points, I agree that regardless of the continued use of 'PME' or a separate protective conductor, monitoring should (and eventually will) start to get some serious use.  There's no real technical barrier to it even now, and there are already smart meters in some countries that report strange voltages that could indicate a neutral problem. Much more can be done, including the use of multiple measurements together. But various issues of tradition, poor communication channels, no low-price products being pushed hard, not huge gains (serious accidents seldom, serious damages awarded even more seldom) limit the speed of uptake.

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