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Electrical Vehicle Charging Points - True earth on solid floor

Apostolos
Good afternoon.

The problem with EVC Points in a few words is that it introduces the PME (the MET in reality) voltage on the metallic car body. Then, if someone touches the car (under PME voltage) and stands on the ground touching the TRUE EARTH potential he will be introduced to a high voltage in case of an open PEN incidence. 

There are some gross guidlines ( https://www.electricvehiclechargepoint.com/ev-resources/earthing )that say

-If the EVC is outside then TT is needed (the person touches the true earth)

-If the EVC is inside and no charging happens on the outside then PME can be used (the person does not touch the true earth)

Then my question is:
WHAT IS THE POTENTIAL OF A CONRETE FLOOR IF THE EVC POINT IS INSIDE THE BUILDING????

Why do we assume that the concrete floor inside the building is on PME potential and so the EVC can be on PME?

If it is a metal building then I can see somehow that the concrete floor is in touch with the metal skeleton which is bonded to the MET so the concrete floor could be assumed to be on PME potential (correct me please if I am wrong)

If the building is concrete, how on earth this solid concrete floor is considered to be at PME potential????

 


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  • 0

    Wouldn't the supply be lost as well as the means of earthing?

    Yes, in the case of a broken PEN, the supply would be lost - or at least usually significantly reduced (depending on what remained connected to Earth upstream of the break) - but the broken PEN conductor & installation earthing system would still be pulled towards line voltage by other connected loads in the installation, and while the various pilot functions (often including the vehicle's check of the earth loop) might prevent the charge point's L&N contacts closing, the PE connection (other than in specifically open-pen detecting charge points) would usually remain solidly connected.

       - Andy.

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  • 0

    Wouldn't the supply be lost as well as the means of earthing?

    Yes, in the case of a broken PEN, the supply would be lost - or at least usually significantly reduced (depending on what remained connected to Earth upstream of the break) - but the broken PEN conductor & installation earthing system would still be pulled towards line voltage by other connected loads in the installation, and while the various pilot functions (often including the vehicle's check of the earth loop) might prevent the charge point's L&N contacts closing, the PE connection (other than in specifically open-pen detecting charge points) would usually remain solidly connected.

       - Andy.

Children
  • 0 in reply to AJJewsbury
    AJJewsbury said:

    Wouldn't the supply be lost as well as the means of earthing?

    Yes, in the case of a broken PEN, the supply would be lost - or at least usually significantly reduced (depending on what remained connected to Earth upstream of the break) - but the broken PEN conductor & installation earthing system would still be pulled towards line voltage by other connected loads in the installation,

    I think the truth of the matter is significantly more complex.

    The answer is "Not necessarily" ... there are a few situations that would keep the "lights on full" as it were, chiefly because most PME distribution systems are three-phase:

    (a) the balance on the network may well mean Neutral current is very low (or zero), in which case the touch potential to the general mass of Earth will be kept down. However, the balance can also be such that, on one or more phases, the voltage can still be significant enough to operate equipment, in fact within "normal" limits, with a hazardous touch potential on the supply neutral (and hence PE of the installation) with respect to the general mass of Earth - only one phase may see a "low voltage".

    (b) There could be a sufficiently-low resistance of fortuitous connection back to the supply Neutral, through extraneous-conductive-parts, so that everything seems "normal" - and this again wouldn't necessarily lead to a high touch potential, that is until suddenly something changes.

    (c) Even if the installation is upstream of a break, there are occasions when diverted neutral currents could occasionally cause a local rise of PE potential with respect to the general mass of Earth.

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