SIMULTANEOUS CONTACT QUESTION - 2 x EV vehicles parked next to each other

Scenario

A remote block of 3 garages, 2 will be fed from separate properties via 40m of 10mm EV SWA connected to 2 individual new CU's

( no cars will be parked inside the garages but charged on the drive in front of the garage door)

1 property is TNC-S - Ze 0.30 Ohms and the other is visually a TNS but with Ze 0.32 Ohms and similar L-N reading.

The 2 chargers will have Pen fault protection and the relevant RCD protection as usual.

There are underground services within 1 -10m of a potential TT rod so could be problematic and a maximum 2.5m between separate garage earth rods is possible.


The concern is simultaneous contact between the 2 vehicles.

Regulation 411.3.1.1 states that “simultaneously accessible conductive parts shall be connected to the same earthing system individually, in groups or collectively.”

I am currently waiting for UK Power networks to confirm the 2 properties are connected to the same earthing system.


The questions are:

Is Pen fault and RCD protection enough when connecting both cars to TNS/TNCS or is there anything else we can do?

Is separate TT earth rods along with simultaneous risk assessment the safest option in this case?

Thank you


I've attached a sketch of the current proposal to help explain.
PDF

  • Is Pen fault and RCD protection enough when connecting both cars to TNS/TNCS or is there anything else we can do?

    No, Regulation 411.3.1.1 stipulates clearly that simultaneously-accessible exposed-conductive-parts must be connected for the same earthing system. This is required in order for automatic disconnection of supply (ADS) to work safely (regardless of whether the RCD or an OCPD is providing that automatic disconnection).

    The OPDD only protects against open-PEN faults, and has no impact on ADS.

    Is separate TT earth rods along with simultaneous risk assessment the safest option in this case?

    No ... separate TT systems alone won't help either ... both chargers would have to be on the same earthing system.

    The TT systems could work, if they were bonded together ... but if they are from separate installations, what will make sure the bonding is effective in the future, and who is responsible for maintaining the connection in the years to come?

    I am currently waiting for UK Power networks to confirm the 2 properties are connected to the same earthing system.

    That is the best option ... if they are not, then unless there's any way to prevent simultaneous contact, there doesn't appear to be a simple way of making the arrangement conformant to BS 7671.

  • Hi Graham, thank you for your help with this it is very much appreciated.

    Currently under regs am i right with the following:

    The best & safest option for the 2 clients is:

    1. DNO confirmation of both supplies being connected to the same earthing systems

    2. Pen fault/RCD  protection to both chargers?

    Failing a response from the DNO

    If we were to divorce the PME for both garages and bond both new CU's to one earth rod or condudisc flex( which has up to 4 ways available) complete with relevant labeling/EIC notes, would that satisfy BS7671 and make the installation compliant?

    Kind regards

    DeanW

  • Hi Graham, thank you for your help with this it is very much appreciated.

    Currently under regs am i right with the following:

    The best & safest option for the 2 clients is:

    1. DNO confirmation of both supplies being connected to the same earthing systems

    2. Pen fault/RCD  protection to both chargers?

    Yes, I believe that would be classed as conformant.

    If we were to divorce the PME for both garages and bond both new CU's to one earth rod or condudisc flex( which has up to 4 ways available) complete with relevant labeling/EIC notes, would that satisfy BS7671 and make the installation compliant?

    Yes, BUT ... unless there's some legal agreement from both Clients that this will be maintained, and perhaps who by (may have to go into the property deeds as a Covenant??) I'm not sure it could be relied upon ??

    I'm not a legal professional, but this arrangement of "shared earth" probably needs legal advice (what if one owner removes their charger, and the means of earthing ... leaving the other without a means of earthing, for example)?

  • Thank you once again Graham

    This project has been on my mind forever. I feel reassured that the safety of the client(s) has been optimized and our installation will be compliant to BS7671.

    Fingers crossed with UKPN!

    Kind regards

    DeanW

  • Dean,

    Obviously as you have indicated and good advice from Graham, and maybe its a remote option that could be considered.

    And that would be to install or erect some kind of "Wall/partition" between the two EV charging bays, to prevent similtaneous contact? Might not look pretty and obviously something a car could hit if not being carefull, but if done correctly could perhaps give an option if UKPN confirm the worst, just need to consider the fire rating and combustible nature of any "Wall/partition".

    Cheers GTB 

  • Are we not even allowed to have wooden fences near an EV charger now?

  • Thank you GTB, this could be an option, i was also thinking of maybe putting 2 chargers on one property with load balancing. One of the clients could use RFID to charge the cost to the main electricity account holder. 

    Just another thought!

  • Are we not even allowed to have wooden fences near an EV charger now?

    That might depend on your insurance company's perspective ... and that is not said in jest ... but BS 7671 of course doesn't really have any beef with it.

  • There are streets of pre-war  TT earthed houses near me and I'm sure its not the only  example in the UK, A few have car chargers, and I imagine its only a matter of time before some pair of neighbours do if not already.

    Now they all have rods near the front door, and very much not reliably overlapping electrode zones arise from those. The big shared  unofficial electrode is the lead  service pipes and cast iron water mains that link them, but slowly the lead pipes in the front gardens are changing to blue plastic, which long term may be better or worse for health, but we can be sure its a lot worse electrically as it puts more reliance on the individual household electrodes some of which are in a poor state.

    Don't think anyone installing a charger even thinks about a possible voltage offset between the CPCs of adjacent properties and I'm pretty sure not all the installers check the electrode resistances either.

    The risk is similar.

    Mike

  • Morning Simon,

    Its something that is cropping up far more often now, and also in the small print of terms and conditions of building insurance policies, that I suspect vast majority of people dont even look at.

    Most UK Insurers refer to the FPA RC59 document and guidance and detail in that.

    There is advice when installing charging bays about Min seperation distance to adjacent vehicles but also from properties.

    Because of the jet like flame that could possbly come from a lithium ion battery there is detail about distances from building structures. I have seen some policy terms now that although they obviously cant state that EV charging is not allowed or covered as part of the policy, many are indicating "Charging" needs to take place 10M from a domestic property!!

    Its to do with heat froma potential EV car fire and the impact on the windows and doors of the property and the fire protection offerred by those being defeated.

    Thats why I suggested if a wall/partition was being placed between two charging bays, where EV is being charged from two seperate supplies and earthing arrangements, I would have that wall/partition of suitable non combustible material.

    GTB