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

Parents
  • 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

Reply
  • 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

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