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Risk assessment on street EV

lyledunn

Referring to the RIsk Assessment C1 in the COP Electrical Vehicle Charging Equipment Installations which relates to EV charge points on street when TT systems are employed. Hitherto I have completed the assessment relating to similar installations for commercial/industrial settings without too much bother. However, I have noticed that in Step 1 and step 3 of the on street assessment, the wording is different. Step 1 raises caution of an open pen if the EV is within 2.5m of other metalwork connected to other earthing systems even if those earthing systems are themselves TT (or at least that is how I read it). Is this just an issue of contact or proximity  with underground conductive parts that might be considered connected to the PME system? Step 3 indicates an unsafe situation if it is possible to touch the EV and “faulty street furniture” 

So if I have any item of class 1 street furniture within simultaneous touch of the EV, irrespective of the earthing system to which it is connected, then the implication would seem to be that the installation should not proceed without further measures?

Any clarification would be appreciated.

  • 0

    BS 7671 does not permit a mix of earthing systems (that is, systems, not arrangements) within simultaneous contact distance where ADS. So, you can have two TT systems, or a TN-S and TT system, in simultaneous contact distance, provided they share the same earthing system.

    The relevant Regulations are 411.3.1.1 and 542.1.3.3

    You could bond two TT systems together to meet 411.3.1.1 - but that would only be advisable if they have the same owner/operator, otherwise you couldn't guarantee they would stay connected together. It might also be possible to do the same for a TT system and a TN-S system - and, if we're not considering a place where PME earthing is prohibited without other precautions (717, 722), even a TT and TN-C-S system.

    With two TN systems, however, we need to consider whether they are (and will always be) supplied by the same substation before bonding them together, or HV fault currents might be transferred. Also, if one supply is much smaller than the other, are the main earthing conductors and supply cable protective conductor are up to the job for fault currents of the largest supply - if not, we may not be able to cope with the larger fault currents. These two issues are the subject of 542.1.3.3.

  • 0 in reply to gkenyon

    I was aware of that Graham but just struggling to understand the actual danger in this situation.

  • 0

    I was aware of that Graham but just struggling to understand the actual danger in this situation.

    Presumably the danger between say two independent TT systems is that they might at times be at differing potentials (either due to an ongoing fault or the result of normal protective conductor currents) - so the situation would be similar to an extraneous-conductive-part entering a TT installation and not being bonded.

       - Andy.

  • 0 in reply to AJJewsbury

    Ding!! Thanks AJ!

  • 0

    Presumably when the designer does the design there is an assumption that the car driver will park correctly in the designated bay, however with on-street chargers attached to street lighting columns and the like they can end up on the footway so the designers allowances for separation between earthing systems are no longer applicable.

    This becomes even more of a problem as I am now frequently seeing people who don’t have an off-street parking space, so get as close as they can to their home then park and run a long extension lead out to the car to charge it, which may well be parked halfway over the footway or more within reach of a street lighting column or the like.

    At what point will there have to be strict enforcement of parking rules to keep cars in designated parking bays and bans on charging vehicles from homes without off-street parking with extension leads to keep vehicles on charge in separated earthing zones and to avoid trip hazards from trailing cables? 

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