1. Visiting from the US? Why not try DIYnot.US instead? Click here to continue to DIYnot.US.
    Dismiss Notice

EV charging points

Discussion in 'Electrics UK' started by studentspark, 17 Sep 2017.

  1. studentspark

    studentspark

    Joined:
    13 Mar 2010
    Messages:
    589
    Thanks Received:
    15
    Location:
    London
    Country:
    United Kingdom
    Home EV charging points if TNCS

    Regulation 722.411.4.1
    (ii) requires a very low resistance earth electrode to mitigate the effects of an open circuit PEN conductor fault on the supply.

    Hear two sides to this, some say good, some say bad as could get the load current of nearby customers appearing on the rod if there is a broken PEN

    I do struggle a bit with differing earth potentials.
    and would appreciate some guidance.

    I thought you had to keep all earthing systems separate, so why some say adding a rod to a TNCS is OK, Im not sure.

    Isn't earth potential going to be quite similar, in a local area, or does it fluctuate because of local installations potentially leaking fault current to earth

    If someone has the time to explain , or link to any good articles on this, i would be very grateful.

    Thanks
     
  2. Sponsored Links
  3. JohnW2

    JohnW2

    Joined:
    28 Jan 2011
    Messages:
    48,120
    Thanks Received:
    3,137
    Location:
    Buckinghamshire
    Country:
    United Kingdom
    It's not just 'OK' - assuming things go as planned, as of mid-2018 (when the new edition of BS7671 will be published) there will be a requirement in BS7671 for all electrical installations (including TN-C-S ones) to also have a local earth rod connected to it at each supplied premises.
    Under most circumstances, the potential of 'the earth' will be broadly the same everywhere. However, the problem with a TN-C-S 'earth' is that is actually the Neutral of the supply (rather than 'true earth') and, should that conductor fail somewhere in the local distribution network, it is possible for its potential to rise to considerably about true earth potential, in the worst cases approaching the line potential (i.e. 230V or whatever).

    Kind Regards, John
     
    • Thanks Thanks x 1
  4. ericmark

    ericmark

    Joined:
    27 Jan 2008
    Messages:
    18,225
    Thanks Received:
    1,697
    Location:
    Llanfair Caereinion, Nr Welshpool
    Country:
    United Kingdom
    This is a pass the buck job, with PME the M stands for multi so there loads of earth rods, but it seems TN-C-S does not force the supplier to put in multi earths, but what one needs is these multi earth rods, and as long as there are earth rods at each property not a problem, the same of course with water or gas pipes if every property has them and the earth/neutral is lost then it is shared between loads of earthed items.

    So to require the DNO to fit earth rods is OK, when done they can do every property off that transformer. However if you require individually house holders to fit them, how can you ensure all houses on that transformer fit them together? I have seen the line of copper lumps on the lawn which was the 4 mm earth wire going to a radio hams earth pit when the earth/neutral was broken by road works.

    I can see the idea, if thieves steal copper in the sub station it reduces the fire risk in the homes connected to it as a result, but it should be the DNO fitting them no individual houses.
     
  5. JohnW2

    JohnW2

    Joined:
    28 Jan 2011
    Messages:
    48,120
    Thanks Received:
    3,137
    Location:
    Buckinghamshire
    Country:
    United Kingdom
    Quite so. I had always assumed that the 'M' meant 'a good few', but was very disillusioned when the late-lamented westie told us that it is common for M=2 - one rod at the transformer and the other at the far end of the distribution main.

    Kind Regards, John
     
    • Like Like x 1
  6. SimonH2

    SimonH2

    Joined:
    4 Nov 2010
    Messages:
    5,826
    Thanks Received:
    589
    Location:
    Cumbria
    Country:
    United Kingdom
    How the times change ...
    It must be about 15 years ago now when a friend had a visit from the DNO to physically disconnected the cable from his earth rod because they were changing the village to PME.
     
  7. EFLImpudence

    EFLImpudence

    Joined:
    7 Jul 2010
    Messages:
    37,034
    Thanks Received:
    4,150
    Location:
    Retired to:
    Country:
    Portugal
    Yes, you'd think by now someone would know all the 'right' way to do (electrical) things.
     
    • Like Like x 1
  8. studentspark

    studentspark

    Joined:
    13 Mar 2010
    Messages:
    589
    Thanks Received:
    15
    Location:
    London
    Country:
    United Kingdom
    Oh dear going to need a long earth rod for a fourth floor flat
    But , really! That will be worrying in built up areas, with little open areas and loads of services to hammer into.
     
  9. JohnW2

    JohnW2

    Joined:
    28 Jan 2011
    Messages:
    48,120
    Thanks Received:
    3,137
    Location:
    Buckinghamshire
    Country:
    United Kingdom
    Indeed. We have previously discussed the (im)practicalities, and some people have also expressed safety concerns. If things stay per draft, it is little more than a sentence, so pretty vague without any detail as to how it is meant to be achieved in many situations (such as you mention).

    If it happens, it will be interesting to see what people do!

    Kind Regards, John
     
  10. Sponsored Links
  11. ban-all-sheds

    ban-all-sheds

    Joined:
    27 Aug 2003
    Messages:
    69,782
    Thanks Received:
    2,858
    Location:
    London
    Country:
    United Kingdom
    Did he ask them to remove his main bonding too?
     
  12. SimonH2

    SimonH2

    Joined:
    4 Nov 2010
    Messages:
    5,826
    Thanks Received:
    589
    Location:
    Cumbria
    Country:
    United Kingdom
    No, they left the bonding in place (metal water and gas pipes) - just disconnected the earth rod.
    Yeah, makes a lot of sense doesn't it :rolleyes:
     
  13. JohnW2

    JohnW2

    Joined:
    28 Jan 2011
    Messages:
    48,120
    Thanks Received:
    3,137
    Location:
    Buckinghamshire
    Country:
    United Kingdom
    It probably isn't meant to make sense :)

    Do you think that, if the requirement for earth rods appears in the final version, they will come back when the 18th ed is in force and reconnect his earth rod ?!

    Kind Regards, John
     
    • Like Like x 2
  14. ban-all-sheds

    ban-all-sheds

    Joined:
    27 Aug 2003
    Messages:
    69,782
    Thanks Received:
    2,858
    Location:
    London
    Country:
    United Kingdom
    Even if it didn't make sense, I don't think you have grounds for asserting that it was intended to not make it.
     
  15. JohnW2

    JohnW2

    Joined:
    28 Jan 2011
    Messages:
    48,120
    Thanks Received:
    3,137
    Location:
    Buckinghamshire
    Country:
    United Kingdom
    Don't be silly. As you jolly well know, I obviously did not mean that it was not intended to make sense.

    You must be having another of those quiet days.

    Kind Regards, John
     
  16. ban-all-sheds

    ban-all-sheds

    Joined:
    27 Aug 2003
    Messages:
    69,782
    Thanks Received:
    2,858
    Location:
    London
    Country:
    United Kingdom
    No, not a quiet day. I do not abandon my standards because I am busy.

    The problem is that in another topic you told someone who was objecting to regulations (in part objecting to the whole idea that there should be regulations) that they are not meant to make sense.

    Not helpful.
     
  17. JohnW2

    JohnW2

    Joined:
    28 Jan 2011
    Messages:
    48,120
    Thanks Received:
    3,137
    Location:
    Buckinghamshire
    Country:
    United Kingdom
    You're still being silly. "...not meant to make sense" (with a smiley) is a light-hearted phrase which is quite often used here (and elsewhere), particularly by EFLI and others, when talking about regulations which do not appear to make much sense.

    Why have you suddenly decided to make an issue about this, and in relation to me rather than one of the others who use the phrase? I continue to suspect that you don't have enough work to do today.

    Kind Regards, John
     
Loading...

Share This Page