Rules and Guidelines
Want to participate in the discussions? Please read our Community Rules and Guidelines. Need some help? Visit Support and Answers.

  • State Not Answered
  • Locked Locked
  • Replies 15 replies
  • Subscribers 32 subscribers
  • Views 8221 views
  • Users 0 members are here
Options
You may also be interested in
This discussion has been locked.
You can no longer post new replies to this discussion. If you have a question you can start a new discussion

EV Charging TN-S Supply

Eddie Currents
Recently sat the 18th Edition Course and of the understanding EV Charging points shall be fed from a TT Supply. PME is acceptable only when feeding any other equipment ie Lamp posts Ticket Machines for example and providing Type A or Type B RCD is fitted and the Charger point is then to be separately spiked. Just looking on the attached and a company called Pod Point suggest TN-S is acceptable with no need for an earth spike. Wondered if anyone else has come across this diagram and can confirm TN-S is acceptable without the spike (see - page 2)
  • 0

    Carlwordsworth:
    Image result for tt system




    Almost - there also need to be an earth electrode at the source, connecting N to true earth; otherwise you end up with an IT system rather than TT.


    In consumer's terms, the characteristic of a TT system is just that the consumers earthing conductor is connected to a local electrode instead of the supplier's earth terminal - and as a consequence everything (including submains) need RCD protection.


       - Andy.

  • 0

    AJJewsbury:




    Also you cannot have your TT earthing system being simultaneously accessible to another earthing system, see Regulation 411.3.1.1. So you may need to change Class 1 light fittings adjacent to Class 2 and enclose any nearby pipework.



    Interestingly 411.3.1.1 only requires simultaneously accessible exposed-conductive-parts to be connected to the same earthing system - there's no such demand on extraneous-conductive-parts in that regulation - and normally no demand at all about extraneous-conductive-parts being isolated from the influence of a different earthing system. Which is all quite practical when you consider a typical TT installation which may share a metallic water pipe with next door who uses PME. Common sense might indeed suggest that you would want to avoid the influence of two different earthing systems being within reach of each other - but the regulations don't seem to make that a specific requirement - indeed 714.411.3.1.2 seems to reduce the normal requirements for bonding extraneous-conductive-parts for outdoor systems (including highway power supplies & street furniture) - which arguably EVSE might fall under as well as section 722.

     


    411.3.1.1 is written in line with 114.1, but this is clearly not the case in many conditions where there is a broken CNE conductor. As other threads have pointed out, the "normal conditions" of protective bonding are also not "applicable", and we might therefore expect extraneous-conductive-parts, whatever the installation they are connected to, might be at a hazardous touch voltage with respect to the general mass of earth (and therefore a TT earthing arrangement, where the earth electrode is suitably separated from other buried conductors, including extraneous-conductive-parts, connected to the PME earthing system. The situation also links in 542.1.3.3.

     



    In terms of reducing shock, the aim surely should be to try and keep the EVSE's earth at a similar potential as possible to the ground on which the vehicle will be standing - which isn't necessarily the general mass of the earth. Consider where the installation's metallic water supply pipe runs directly underneath the drive (probably not unusual) - in such cases having the TT electrode moderately close to the pipe so that its potential varied in a similar way to the ground surface would provide better safety than having it a greater distance away to avoid such influence.  A 'ditch tape' electrode around the perimeter of the parking space, regardless of the influence of any other buried metalwork, might be a far more effective approach than attempting isolation from other earthing influences (installation practicalities notwithstanding of course).



    Agreed - the issue being that if the premises has no extraneous-conductive-parts, and there is no other buried metalwork connected to the PME earthing terminal, then an appropriately-positioned TT earth electrode near the parking position may well be appropriate and a lot safer than using the PME earthing terminal, but if there is buried metalwork connected to the PME earthing terminal in small curtilege properties, you might simply be "returning the PME touch voltage" and have little or no improvement. There are a lot of variables at play here in the earthing "landscape" under and around the building.


    This earthing "landscape" is also different on-street.


     

  • 0

    Also you cannot have your TT earthing system being simultaneously accessible to another earthing system, see Regulation 411.3.1.1. So you may need to change Class 1 light fittings adjacent to Class 2 and enclose any nearby pipework.



    Interestingly 411.3.1.1 only requires simultaneously accessible exposed-conductive-parts to be connected to the same earthing system - there's no such demand on extraneous-conductive-parts in that regulation - and normally no demand at all about extraneous-conductive-parts being isolated from the influence of a different earthing system. Which is all quite practical when you consider a typical TT installation which may share a metallic water pipe with next door who uses PME. Common sense might indeed suggest that you would want to avoid the influence of two different earthing systems being within reach of each other - but the regulations don't seem to make that a specific requirement - indeed 714.411.3.1.2 seems to reduce the normal requirements for bonding extraneous-conductive-parts for outdoor systems (including highway power supplies & street furniture) - which arguably EVSE might fall under as well as section 722.


    In terms of reducing shock, the aim surely should be to try and keep the EVSE's earth at a similar potential as possible to the ground on which the vehicle will be standing - which isn't necessarily the general mass of the earth. Consider where the installation's metallic water supply pipe runs directly underneath the drive (probably not unusual) - in such cases having the TT electrode moderately close to the pipe so that its potential varied in a similar way to the ground surface would provide better safety than having it a greater distance away to avoid such influence.  A 'ditch tape' electrode around the perimeter of the parking space, regardless of the influence of any other buried metalwork, might be a far more effective approach than attempting isolation from other earthing influences (installation practicalities notwithstanding of course).


    722.411.4.1 has changed quite recently - I'm not sure its evolution is yet complete.


      - Andy.
  • 0
    That`s the plan - thank you
  • 0
    Carl


    If you are going to make the charging point a TT Island then you need to carefully follow Graham Kenyon's advice about your electrode being spaced away from any underground metallic pipework connected to a PME earthing terminal.


    Also you cannot have your TT earthing system being simultaneously accessible to another earthing system, see Regulation 411.3.1.1. So you may need to change Class 1 light fittings adjacent to Class 2 and enclose any nearby pipework.


  • 0
    Image result for tt system
  • 0
    That's exactly what we are thinking at the moment. Also a traffolyte warning label at origin. Thank you
  • 0
    Actually reading your description of the transformer and gensets, it sounds to me like one of the few cases where it is always going to be  TNS, and you can proceed to use the system earth.

    Nothing to stop you leaving a note at the origin saying that the charging points use the TNS earth, and if this is ever changed the earthing of the charge points must be re-visited. In all systems you can bond an additional earth rod to the supply earth at any point, much as you can add a water pipe bond at any point, so you can be TT ready but linked to the TNS if you wish.

  • 0
    It is a tricky one. We will take a good look at the COP and also the earthing arrangements before we make a final decision. Many thanks for the information.
  • 0
    There are, however, a number of serious safety concerns with making a separate TT earthing system for the charge points, not least:
    • there must be no possibilityof simultaneous contact between the vehicles on charge, and exposed- or extraneous-conductive-parts in the original installation (this is a basic requirement of BS 7671).

    • there must also be separation underground, between the earth electrode(s) for the charge points, and any buried metalwork and exposed conductive parts connected to the PME earthing terminal. Some DNOs have minimum separation requirements of as much as 3.6 m. I would also be wary about the earthing arrangements for the HV transfromer.


    An alternative is to use an isolating transformer for each charge point, but this comes with a cost.


    To complete this installation safely, sounds like it's not an east one. It's definitely worth getting a handle on the earthing arrangements ... as has been said, working to the Code of Practice strongly recommended.


Community Rules & Guidelines