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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

    John Peckham:

    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.

    Really ? - in terms of delivered kW/h etc etc, just how many system neutrals have gone AWOL in 50 years, and caused significant deaths or injury - compared with the rest of the non PME infrastructure. Sure, things like CONSAC cable didn't help, but at that time we had Aluminium, by the world price of copper was through the slates due to various unpleasantness going on


    Not all European countries use PME earthing.

    But a number do - start with the boxheads for one


    I gave a presentation on the hazards of PME and vehicle charging

    Again - this is a total shambles by the people involved  - how many people died plugging in a granny lead to the nearest socket ? - there is a hazard, but in may cases not greater than the hazard of using any electrical system - despite the zeal over this issue, it does smack of late to the party and coming up with a problem so a solution could be fitted to it. How is a car charger that unsafe compared to any other external piece of electrical equipment in a cabinet (generally speaking from the PME perspective)



    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? 

    Sure - what people of my generation would call the "ditch tape"  - or more technically a foundation electrode combined with a perimeter tape and rods (hollow square added to the slab resistance to get a reasonably low resistance combined electrode) - something I've been doing for decades on designs that require LPS systems. For non UK projects, it's the starting point for most earthing design, anyway




     

    Regards


    OMS
  • 0
    Interestingly John I have a suggestion which would probably make this TN-S system little more expensive. In fact we are only interested in faults in earthed properties via the DNO cables, not on the network. This means that the earth core needs a fairly small cross section, and the substation has a "grown up" sized earth fault relay which isolates the HV if the earth fault current becomes enough to cause a cable failure. This would be reasonably cheap and simple, so why not? Suggesting that when the whole network is rewired, and this is certainly what is needed for this "all electric future" adding a few percent to the cable price is not much of a problem, particularly as the civils cost will be much more than the cables.
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    Can we all agree these situations?


    1.  A new build housing estate of a few hundred house on a green field site.  New transformer(s). DNO compelled to provide a TN-S  supply to all properties with earth electrodes laid in the trench connected to every joint earth?

    2. A new cable run out from a sub-station as a replacement or a new supply to be TN-S?

    3. If the DNOs were compelled to upgrade their networks as the water and gas services have been doing for years (why not a requirement as gas and water) the new supplies would be TN-S?


    Yes the DNOs are under a statutory duty to maintain their neutrals but they do not consistently and as far as I know the HSE have never prosecuted any DNO for not maintaining their neutral connection. Regulation 114.1 of BS 7671 suggests we do not have to consider the loss of the neutral when designing an installation, but we do.


  • 0
    Yes David, digging the 'oles is the most expensive bit but why not spend an extra few quid on the cable to get a superior earthing system? Yes there will still be the risk of over voltages in the event of a lost supply neutral but the the shock risk of anyone touching exposed or extraneous conductive parts is massively reduced. Also no need for compensatory measures to mitigate the shock risk.
  • 0

     (I'd support a campaign of testing ZS and labeling cut outs with the result whenever a DNO visits on any system)




    In North Norfolk, where a whole village is upgraded from bare overheads to A.B.C. overheads, U.K.P.N. supplies a white sticky label that is affixed on the main cutout. On it is hand written the Zs value after testing. That is very helpful.


    Z. 

  • 0

    John Peckham:

    Can we all agree these situations?


    1.  A new build housing estate of a few hundred house on a green field site.  New transformer(s). DNO compelled to provide a TN-S  supply to all properties with earth electrodes laid in the trench connected to every joint earth?

    2. A new cable run out from a sub-station as a replacement or a new supply to be TN-S?

    3. If the DNOs were compelled to upgrade their networks as the water and gas services have been doing for years (why not a requirement as gas and water) the new supplies would be TN-S?




    Afraid not! ?


    1. Yes, I do agree with most of this one. I am not sure about the need for all those earth electrodes. Legislation would, of course, need to be amended. It would also be necessary for the law to require DNOs to maintain TN-S installations as such.


    2. Yes and no. Yes if new, no if old. That's because you couldn't guarantee that all the service cables would have maintained separate N and PE.


    3. No. Unlike with gas supplies, you cannot just shove a new wire up an old one.


    The underlying problem is that whilst it is easy to go from TN-S to TN-C-S, the reverse is not the case, so slowly but surely the LV network has been "PME'd".


    I suspect that part of the problem was deterioration of PILC junction boxes and that TN-C-S was seen as a way of avoiding it. So now most of us are stuck with it.

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    Kelly Marie:

    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




    I know for certain that SSE "PME'd" my service cable (and urgently too) 'cos I saw them do it. ?

  • 0
    Regarding the reporting of lost neutrals - to whom would this be done? I don't even know whether there is any obligation to keep records internally.


    In the countryside it may be fairly common. A fellow member of a motoring club mentioned problems twice after storms this winter. He was puzzled that the supply voltage had dropped to somewhere around 25 V on one occasion and 70 V on another. LED lights were working, but not things with motors such as the fridge. He was rather non-plussed when I suggested that the line voltage may not have dropped at all, but the neutral may have risen. In fact he challenged the notion that it was possible with a TN-C-S supply.
  • Former Community Member
    0 Former Community Member

    Chris Pearson:


     


    Kelly Marie:

    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




    I know for certain that SSE "PME'd" my service cable (and urgently too) 'cos I saw them do it. ?


     



    However, if they are going to formally declare PME on the  system, the DNO also has to ensure that relevant electrodes are in place at source end and penultimate service position branch along with a few other well defined locations along the way. They may well also need to connect the end of the distributor (the PEN) to another adjacent distributor PEN as reinforcement before they can actually state the service is PME. It's actually not as haphazard as it might seem - and DNO's wont do it unless all the prescribed electrodes are in place


    It is probably worth pointing out that even if the PEN goes AWOL, there are usually several other local consumers shunting the system so the voltage rise is usually constrained


    Regards


    OMS


     
     

  • 0

    Zoomup:




     (I'd support a campaign of testing ZS and labeling cut outs with the result whenever a DNO visits on any system)




    In North Norfolk, where a whole village is upgraded from bare overheads to A.B.C. overheads, U.K.P.N. supplies a white sticky label that is affixed on the main cutout. On it is hand written the Zs value after testing. That is very helpful.


    Z. 


     




    I stood next to a DNO jointer whilst he tested a new supply, he said they use fault current rather than Ze to determine  if the connection is sound. it is after all a live-neutral loop they are testing to see if the fuse will blow.


    Andy Betteridge.

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