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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?
  • Former Community Member
    0 Former Community Member
    PME is not inherently unsafe - there is no evidence to say that's the case in 50+ years of deployment - and it does have some advantages that loss of earthing is quickly noticed


    That said, the driver was, is and always will be cost  - be that in the public or private sector (why do you think we built critical infrastructure in flood zones - ohhh yes, the land was cheap)


    So called Global earthing will be with use for a long time yet, despite the introduction of polymeric cables - and it has to be said, that the insulation advantages combined with earthed screens still outweighs older cable types - installing MIND PILC is an expensive business from a capital perspective


    Like all these things, we seem to want a Rolls Royce system, but society doesn't want to pay


    Given that PME is also widely used across Europe and beyond I can't see any appetite to change now - similar to transmission pylons and wind turbines I guess - cheap and effective but not well liked in some neighbourhoods - in an ideal world we wouldn't start from "there"


    Regards


    OMS
  • 0
    While I can offer no technical insight, I support your campaign due to the issues we have around bonding and exporting PME especially if there are metallic services in the receiving building. Then we are told that TNS installations are most probably PME anyway so we stuff even more copper into each installation. 


    The only downside, if it is one, is that if PME is banned then we will probably be told to TT every installation. Not something I would necessarily object to if it were not for the unreliability of RCDs and the issues around metal consumer units and similar assemblies.


  • 0
    I'd support some sort of TNS or SNE (separated neutral and earth)approach to distribution as being slightly safer.

    It also has the advantage of allowing an earth fault transformer (like the RCD sensing part) at the substation, allowing the substation to call in (or even disconnect for) earth faults, and the lost PEN giving rise to a live chassis becomes impossible.

    However, it does not eliminate the more general 3 phase loss of neutral problem, and may make the extremes of fault voltage seen by single phase equipment worse, but of course side effects are contained to equipment damage, not loss of life.


    There is not much real evidence that PME is very dangerous, at least when well maintained. After all while A and E is full on  Saturday nights, it is not the victims of the electrical network that clutter the cheap plastic chairs... 


    So for new work and repairs, SNE may be preferred, but it is not possible on safety grounds to justify taking out existing PME.


    A better approach may be to regulate the  inspection and reporting of PME installations so that dangerous situations are spotted sooner, before something fails and the first warning is is customers calling in with flashing lights and tingles off the taps (I'd support a campaign of testing ZS and labeling cut outs with the result whenever a DNO visits on any system)
  • 0
    OMS


    I profoundly disagree with you. I have the official stats. for the REPORTED incidences of lost neutrals which are a bit like the Corona Virus statistics from China.


    Not all European countries use PME earthing. I gave a presentation on the hazards of PME and vehicle charging and there was a representative from the equivalent of JPEL from another EU country in the audience, I asked how they managed the problem in his country, he said we do not use PME  mostly TT and they would never adopt PME. At another event ere was an engineer from another country where they have employed Foundation earthing since the 1960s as a compulsory measure in their equivalent of building regulations because of PME and to re-enforce global earthing. I suspect that provision will be coming our way in the near future?
  • 0
    In one of the recent EV charging threads there was a link to SSEs LV manual I read some of it and it looked like it said that SSE don't turn existing underground cables into PME by earthing the neutral whenever there is a a repair or extension done if I've read that right maybe DNOs are less than keen on it too. Anyone know for certain if this is the case? I bet UKPN will chirp in soon if he is still about
  • 0

    .. I have the official stats. for the REPORTED incidences of lost neutrals 




    Are you able to share those?.. Link? 

  • 0
    Justin regrettably not which I know some forum readers will believe that I am not being truthful. 


    This may give you some useful information  https://www.whatdotheyknow.com/request/lost_neutral_resulting_house_fir
  • 0
    Why do we need to second guess the integrity of a supply arrangement provided under ESQCR? If TNCS has integrity problems then statutory obligations are not being met by the network operators. Trying to address  such things in an electrical installation standard such as BS7671 seems to me to be a strange approach. 

    Had 722 said nothing about loss of neutral on TNCS then the first incident would have directed the legals to the DNO. As it is, failure to have some kind of measure in place to mitigate the risk leaves the DNOs off the hook. 


  • 0
    John

    I can see the implementation of what you are suggesting on domestic properties as relatively easy, but in larger more complex buildings I think it would be impossible to apply.

    Just my ten-penneth


    Colin
  • 0
    It might be a good start if the HSE added 'broken PEN' to the long lost of things that must always be reported under RIDDOR. Right now I am told, (purely anecdotally) some DNO encourage their employees to fix these things 'silently' so unless it is really spectacular and ends up on the news  (remember  Briarcliffe school - a good few years ago ) it is just a call out, the hard pressed linesmen go into the substation block, or up a pole, do some magic, the power goes off and then is restored, and the lost PEN part misses the official stats.

    I can well believe it is more common than it appears. Certainly the event I have truly first hand experience of,  was attended quickly enough, but as far as I know went no further than a report of power cut affecting a few houses due to overhead line failure - while I know our neighbour had shocks from her appliances in the kitchen, and therefore came round to see us in quite a 'tizzy'. We were TT on the same TX, while the neighbour had PME, so all we had was dim lights.



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