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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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    Andy and others


    We are going to need to replace the LV network anyway for two reasons. Firstly a lot of it is approaching  a 100 years old, my supply cable from my local Tx and the cables in my road date back to the 1930s. Secondly if we are going to go all electric for heating and car charging the LV network will need a massive upgrade.


    If the money, probably tax payers money, is forthcoming then this is a once in a century opportunity to get it right and have a robust supply and a  safe earthing system. Specifying the new network should be engineer lead and decisions not made by bean counters and commercial interests.
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    We are going to need to replace the LV network anyway for two reasons. Firstly a lot of it is approaching  a 100 years old, my supply cable from my local Tx and the cables in my road date back to the 1930s. Secondly if we are going to go all electric for heating and car charging the LV network will need a massive upgrade.



    Unfortunately I can guess at some counter arguments on that score. I guess PILC cable doesn't age in quite the same way as PVC (or indeed rubber) insulated cables - many, as you say, are approaching a century in constant service and most still seem to be in adequate condition - is there any evidence that they're about to fail anytime soon? Or might there be some optimism that we might be able to squeeze another few decades out of them?


    On the electricity for space heating debate - if the (building) engineers rather than bean counters have their way - it'll be accompanied by a massive upgrade in thermal insulation - so space heating demand could potentially be quite modest (perhaps 2 or 3kW) per home - and then only at the coldest times of year - or even less if via heat pump - so perhaps then manageable with comparatively modest reinforcement?


    Likewise with EVs - if properly controlled - much charging could be spread around times when the network is less than fully utilised - so the increase in peak demand could be quite modest.


    For sure some re-inforcment will be needed, and we'll have to be a lot cleverer about load control (things like local load shedding, wider smart-meter control and load-shifting by heating stored hot water rather than instantaneous) but I don't see complete replacement of the LV network as inevitable.


    I share you dislike of PME, but I think we're going to have to find better route...


        - Andy.
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    I'm 100% behind JPs TNS advocacy - We should never have left it unless all PME was via underground on a national infrastructure basis - no overheads allowed, so the risk of loss of neutral wholly mitigated.

    How much would that cost to achieve in comparison with what JP is advocating I wonder?.
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    As an aside, I hate TT.It is a poor excuse for not achieving disconnection times for a OCPD. If RCDs are effectively acceptable as a sole means of protection, then why not omit the requirement for mcbs/fuses altogether?

    Not only that, but in the majority of instances around where I operate, it is wholly impractical for the same reasons as those expressed in the electric vehicle charging threads.

    My operating environment is limestone rock-ridden and pretty much impenetrable without the judicious use  of black powder - something which is frowned upon these days unless you belong to a certain section of society.

    Whenever I come across a TT installation locally,  I immediately get the DNO in to PME it.

    That way, they get the responsibility of maintaining it rather than me.
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    This is just an opinion, but to my mind, any TN-Cx system is inherently unsafe.


    The protective conductor should be entirely separate from current carrying conductors.


    In my day to day (before lockdown) job, i classified them as tn-c-s.


    If it happened in my own home, I'd drive a couple of rods, install an upfront RCD, call it TT, and berate the DNO for a failure to provide a safe earth connection.
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    It may be that TNx has its place in towns and is the safest thing if the neighbours have it too, but TT is useful, and with an up front RCD , Fuses and MCBS can be reserved for clearing  L-N faults and overloads , and can take up to 5 seconds to act - they are not an electrocution consideration now, only a fire hazard mitigation.

    TT is much nicer for farms and things like stables with earth floors - I'd far rather have the metalwork of the building and the electrical 'earth' at the same voltage as the ground beneath my feet.
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    Another option is that consumers have to have an earth electrode to tie the neutral to earth MEN, but with a realistic minimum Ra of say 20 ohms for new installations without a requirement to start trying to upgrade existing installations in flats and similar situations.


    On the other hand the DNO could install more electrodes in their network.


     Andy B
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    Mike


    I would agree but. I don't want to rely on anything mechanical or electronic for my shock protection. I am a great believer in passive protection in the form of earthing and bonding. Hence my keenest for a supplied reliable independent earth with the supply with additional multiple earth electrodes at each place where the cable is jointed and foundation earthing for each building. 


    These actions on would require-enforce the Global Earthing system that will be lost from replacing the old rotting PILC cables with modern plastic cables. These rotting cables are like the roots of a mighty oak tree about to be replaced with the roots of a daffodil.


    Goverment will in the near future be asked to fund  the replacement of most of the aging network by the commercial interests , now is the time to push for a much improved  and safer distribution network. We can then stop having to invert and deploy compensatory measures to overcome an inhearantly unsafe earthing system.
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    Sparkingchip:

    Another option is that consumers have to have an earth electrode to tie the neutral to earth MEN, but with a realistic minimum Ra of say 20 ohms for new installations without a requirement to start trying to upgrade existing installations in flats and similar situations.


    On the other hand the DNO could install more electrodes in their network.


     Andy B




    So what is to be done in an area that has very sandy nonconducting soil, especially if it is very dry like now, as it hasn't rained here for about 8 weeks?


    Or, in an area that has very stony ground with many pebbles,


    Or in an area with houses on hard rock?


    Edit. Add link.

    https://blog.nvent.com/erico/erico-what-is-soil-resistivity-and-how-does-it-affect-grounding/


    Z.

     

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    I believe that’s why MEN with consumer electrodes is used in Australia, isn’t TT is banned in both Australia and New Zealand?


    Do you have a British Geological Survey resistivity map on your wall, I have actually considered getting one and framing it to hang on a wall at as it looks very decorative and rather a talking point. I think I might just get away with it, so long as it was by my desk in a spare bedroom.


    Andy B




     Andy B.

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