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EV install on a TT system - DNO PME?

Former Community Member
Former Community Member

Hi, new to this forum.

These might be obvious questions but I can't find an answer to it. 

Background.

A domestic house has a TT supply, has had a CU changed in 2019 but the new owners have no paperwork.

I can find no evidence of an earth rod anywhere and all the bonding cables go to the gas/water supplies. I did a quick Zs at the board = 2.9ohms. 

How do I know if the installation has been PME'd on the pole? (overhead wires)

Second part is - they want an EV charger installed that they brought with them from their old house. It will require TT, but as this property is TT it shouldn't need to have a separate rod.

If the installation is  a PME'd TT I would assume I would need to TT the EV?

  • 0

    Ask the DNO to tell you which earthing system is installed.

  • Former Community Member
    0 Former Community Member

    i'm trying this - but it's octopus and they won't speak to me as I'm not their customer!

  • 0

     

    How do I know if the installation has been PME'd on the pole? (overhead wires)

     

    Clues: Notices affixed to the poles. Earth rods installed at the base of poles, especially at the last one in a run of poles.

    Your installation earth rod may be buried under stuff and not be visible. Your Ze is very low for just a rod. Around here I get about 100 to 200 Ohms for a rod resistance.

    Loop tests on P.M.E. earthed installations normally show a figure of 0.35 Ohms max. at the main earth terminal.

    As Chris says, put in an official request to the distributor for the info. via the home owners if necessary. An application for a P.M.E. supply starts with the distributor surveying the install to confirm the possibility. Around here a  new P.M.E. earth terminal is installed at no cost.

     

    Z.

  • Former Community Member
    0 Former Community Member
    You can't have a PME'd TT system. You need to trace the main earth from the CU, and see if it goes to the incomer from the DNO, or if it goes off somewhere else. By looking at the service head, you'll see if there is an incoming earth which comes from a separate sheath (TNCS, in which case assume PME as this could be the case now or in the future) or from the neutral inside the service head. You can see some examples here in our EV's and earth rods video https://youtu.be/M51_BX1_4XI which i hope helps.
  • 0

    Are the DNO not obliged to give this info to anyone reasonably requiring it ? i.e. the Electrician

  • 0

     

    If the installation is  a PME'd TT I would assume I would need to TT the EV?

    If the installation is P.M.E. earthed it will have an official P.M.E. earth terminal installed and a notice informing us of that. If the installation is TT earthed then the home owner is responsible for providing an earth electrode and suitable R.C.D. protection for the whole installation.

     

    The TT earth electrode has to be visible for inspecting and testing.

     

    411.5.

     

    Z.

  • 0

    The Water and Gas pipes may be providing a good earth depending on the ground condition and may be picking up the earthing arrangements of other properties although high for for a nearby TNCS or TNS. 

  • 0

    What is the earthing conductor connected to? This assumes there is a an earthing conductor?

     

     

  • 0

    KevinF: 
     

    i'm trying this - but it's octopus and they won't speak to me as I'm not their customer!

    Whilst Octopus may be the supplier (on the energy bills) …  they are probably not the DNO.

  • 0

    Zoomup: 
    Clues: Notices affixed to the poles. Earth rods installed at the base of poles, especially at the last one in a run of poles.

    If the installation is P.M.E. earthed it will have an official P.M.E. earth terminal installed and a notice informing us of that.

    It may not be possible to see all the poles and in any event it is possible that none of them has an earth.

    Not all PME supplies have a notice attached to them.

    Is it not reasonably obvious from the origin/CU which earthing system (TN or TT) is installed?

    It is forbidden to use a gas pipe as an earthing electrode, and a metal water pipe may be used only if it is not a public utility supply. 542.2.6

     

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