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EV Charger mounting post - earthing arrangement

Martin Johnson

I'm looking for advice for mounting an EV Charger on a metal post that a customer has installed for this purpose, it's located in his parking space on his driveway. The charger he has purchased is a Pod Point model which has inbuilt PEN fault detection. The armoured cable to supply it will be protected by a double pole type A RCD. The supply is PME. My thoughts are:-

  1. The metal post set in the ground is an extraneous conductive part. The EV charger earth will not be connected to this metal post and therefore there will be a small potential difference between it and the car charger earth (which I guess is connected to the car?)
  2. I don't like the idea of bonding the (PME) supply to the metal post.
  3. Has anyone installed an EV charger on a metal post?  Several manufacturers sell them as accessories to their range of EV chargers, nearly all have built-in PEN protection now.
  4. All advice and comments will be gratefully received.
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    My gut instinct is to bond it to the charger's PE contact DOWNSTREAM of the broken PEN device - i.e. so it's disconnected during a broken PEN event - but remains bonded to the car's metalwork (if plugged in) regardless.

    Regs wise that's probably dodgy as extraneous-conductive-parts are meant to be main bonded and it's likely that neither the EV circuit's c.p.c. nor the PE contact are rated for use as a main bonding conductor. (In practice I doubt that the post will have a low enough resistance to Earth to sink much in the way of diverted N currents, so the physics suggest there will never be a problem, but BS 7671 doesn't seem to let us take account of that.)

    My 2nd thought is to acknowledge that we rarely bond extraneous-conductive-parts outside buildings (the wording of the reg seems to date from an era when the regs were entitled ‘Regulations for the Electrical Equipment of Buildings’) and IIRC the latest DPC suggested that the wording be adjusted to suggest that main bonding need only apply within buildings. Unless you've got a buried grid or some insulating surface over the ground, bonding a few metallic parts outdoors isn't going to do anything useful in terms of creating an equipotential zone anyway - far from it. So just leave the post unbonded and so let it assume the same potential of it's environment (perhaps other than the EV itself).

    That's all presuming it's just an extraneous-conductive-part and not also an exposed-conductive-part (as a metal cased charge point might be).

       - Andy.

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    My gut instinct is to bond it to the charger's PE contact DOWNSTREAM of the broken PEN device - i.e. so it's disconnected during a broken PEN event - but remains bonded to the car's metalwork (if plugged in) regardless.

    Regs wise that's probably dodgy as extraneous-conductive-parts are meant to be main bonded and it's likely that neither the EV circuit's c.p.c. nor the PE contact are rated for use as a main bonding conductor. (In practice I doubt that the post will have a low enough resistance to Earth to sink much in the way of diverted N currents, so the physics suggest there will never be a problem, but BS 7671 doesn't seem to let us take account of that.)

    My 2nd thought is to acknowledge that we rarely bond extraneous-conductive-parts outside buildings (the wording of the reg seems to date from an era when the regs were entitled ‘Regulations for the Electrical Equipment of Buildings’) and IIRC the latest DPC suggested that the wording be adjusted to suggest that main bonding need only apply within buildings. Unless you've got a buried grid or some insulating surface over the ground, bonding a few metallic parts outdoors isn't going to do anything useful in terms of creating an equipotential zone anyway - far from it. So just leave the post unbonded and so let it assume the same potential of it's environment (perhaps other than the EV itself).

    That's all presuming it's just an extraneous-conductive-part and not also an exposed-conductive-part (as a metal cased charge point might be).

       - Andy.

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