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EV CHARGING EQUIPMENT

John Peckham
I am hearing from my network of contractors, that have actually read the new 722, that they have been asking charging equipment manufactures for documentary proof to comply with Note 5 of 722.411.4.


They are getting knocked back for asking or in one case a Declaration that says the particular device complies with BS 7671. I think that is wrong to declare that as BS 7671 is an installation safety standard and not a product standard. I believe that as a minimum the equipment must comply with the Low Voltage Directive and be CE marked. I also believe that manufacturers have to issue a Declaration of Conformity. 


BS 7671 722 has numerous references to the various standards required such as BS EN 61851 that the equipment must comply with. I am thinking it may be illegal to offer the sale of equipment that does not comply with the Low Voltage Directive and is not CE marked?


I am hoping the countries top man of equipment safety standards, Paul Skyrme , sees this post and will come on and give us his expert view?


Has any forum member asked for a Declaration of Conformity from EV charging equipment manufacturers and received one?
  • 0

    mapj1:




    • If the TT electrode is too close (say within 1 m), it's effectively touching PME, so you've not got separation and therefore no point in the electrode. You also need to allow for ground subsidance.

    • You might well then want to argue about the person not standing at the "general mass of earth", but sometimes the voltage drops off quite quickly, even a couple of metres, and there's no guarantee the potential at the feet of a person will be that at the TT earth electrode.

    • Conversely, and because of the previous point, in small curtilage properties, you might well be standing over some metalwork (say incoming gas or water pipe) connected to the PME earth, and in certain cases, you simply return the  PME touch voltage ... this of course means that going to the trouble of TT in many dwellings is pointless !

       


    I'd like to comment on  that.

    If that was really true, then we would have a safety problem getting into the car, even when the charger is not present, as you are suggesting that significant step voltages are  present due to the house earthing in normal operation, and the car is bridging them.

    Where there have been I think 3 deaths of humans from exposed step voltages, and more dogs and some famous horses in the last decade or so, as far as I recall,  these have all be associated with damaged or unterminated underground cables exposing live. As regards earthing faults,  There has been 1 plumber killed by  live buried water main that was acting as CPC until he interrupted it.

    In contrast there are a some  hundreds  of  lost neutral events per year in the UK, and this compares with other countries that use aluminum armour on their underground cables.

    In practice the surface potential appearing due anything buried at all but the shallowest level is not present as a narrow stripe above the object, rather the surface potential  is a sort of diffused average value with ripples due to sources below, and changes gradually.  Surface finish such as tarmac or concrete are significant, hence the preponderance of free-draining gravel at substations.

                 

     


    Have a closer look at the diagram in the previous post, and a read of the relevant Annex in the IET CoP. We're not simply talking about a 1 m step potential, but the TT earth electrode being separated > 2 m (in some cases, DNOs have required separate > 3.5 m). In addition, the shock risk curve considered is wet hands to foot (wet condition, large contact area), not foot to foot.


    I concur that tarmac or concrete changes the shock risk, however - there is a note to this effect in the CoP - but that only reinforces the "TT'ing is pointless" comment I made. However, we must remember that some people in "average semi's" do still get into their car from the flower bed or lawn.



    It is also worth remembering how RCD blinding works - the core of the current transformer saturates in one direction, so once all the magnetic domains have rotated to align with the external field, and no more can move, it behaves more or less  as an air core, rather than a ferromagnet, and does not 'come unstuck' and start to act as a transformer again, except for those parts of waveform where  the sum of the AC and the DC is back in the linear part of the magnetisation curve, i.e. within a few tens of mA of zero.When the AC term is large, the detector side waveform is largely un affected by the DC  (and the secondary voltage is far from sinusoidal.. ), while when the DC is larger than the AC, no signal is  detected. What happens  in between is slightly unclear as it depends on how well   the detector circuit responds to a 'chopped-up' sinewave where half cycles of one polarity are much peakier than the other.  

    I suspect that manyt A type RCDs are just AC designs revisited,  perhaps with a slightly bigger core. Certainly the sensitivity to half wave rectified DC is about half that to a sine wave which would be consistent with this.





    In Mode 3 charging, we also consider pulsed DC because the pilot pulses +12 V then -12 V alternately in part of the sequence. Hence consideration of Type B or RDC-DD.

     

  • 0
    The only reasons for those recommended separations is to make it hard to create an installation where your victim can be caught straddling 2 zones that may be at different voltages - if humans were smaller and had shorter limbs, the recommended distances would be less. Equally the separations would not be good enough for horses or cows, but lickily for us they do not write the regs. Similar consideration applies to the distances for sockets in UK bathrooms (though why is not clear as the rest of the planet has no issue).

    For a vertical rod electrode, in more or less uniform soil - note comments about surface finish - most of the volt drop is within one rod length of the centre - the diameter of the live 'carrot' shape of earth around it scales with length.  A short high impedance electrode (like on the rod tester) has a zone of influence that may be a few inches across.  We are not always sinking 8 ft DNO sized rods - in a domestic setting it may be lucky to be more than a couple of feet and less than a hundred ohms.


    In the car case it becomes more complex, as we have two mobile electrodes, weakly grounded, namely the user, and the car, as well as the more obvious fixed ones associated with the supply and the armour of cables and so on, as well as probably various items like gate posts, fences and so on that bring the average of the terra-firma potential beneath them to places it may not otherwise be  accessible to touch.
  • 0

    mapj1:


    In the car case it becomes more complex, as we have two mobile electrodes, weakly grounded, namely the user, and the car,




    Is the car actually an "electrode"? I agree it's sitting on tyres, and the tyres are made to discharge static, but I believe the resistances are of the order of 1010 Ω taking this well outside the ballpark of even the concrete or tarmac we were discussing earlier?

  • 0

    mapj1:

    The only reasons for those recommended separations is to make it hard to create an installation where your victim can be caught straddling 2 zones that may be at different voltages -




    The separation distances that "keep cropping up" in the case of separation of TT systems (2.5 m, 3.5 m, 10 m) are actually based on Figure 16 in BS 7430.

  • 0
    Great deliberation and effort by installation and product engineers is obviously being directed at the consequences of loss of neutral on a TN-C-S system. I wonder if such focus is being applied by the network engineers in the DNOs in respect of their statutory obligation under ESQCR to take all reasonable precautions to ensure continuity of their neutral. Indeed, my reading of 7671 regulation 114.1 was that the designer of an electrical installation could make the assumption that the DNO neutral was permanent.

    If a network neutral is lost then it is highly likely that there has been a weakness in the safety system applied by the distributor and that a breach of statutory obligation could be identified. If, as reported, there is one loss of neutral incident per day, then clearly there is an issue on the network side. That issue really shouldn’t result in unnecessary fixes on the consumer side. Rather, if the government want expeditious roll-out of EVs then perhaps the HSE should be directed to vigorously clobber each loss of neutral incident.
  • Former Community Member
    0 Former Community Member
    So, at a friend's house there is a 6 mm^2 bond to an up-and-over garage door, fitted so far as I can tell when the house was built in 1990. I would expect all the houses on this estate to have them though I haven't checked. Now would anyone like to argue that the risk associated with this large metallic surface with a conductive handle, touched regularly whilst standing on the driveway and connected to a PME-labelled earth terminal is significantly different to the car plugged in on the driveway?


    Yes it could be argued that this connection could be removed, though on a wet and windy day perhaps the door measures just a few kiloohms to true earth and it is simultaneously touchable with a bonded metallic gas pipe. It may even make contact with the pipe some of the time, at the moment there's a ~1 mm gap but that could easily disappear.


    I am unconvinced that there is a new risk associated with TNC-S and electric cars, rather that the risk is comparable to the others that have existed since the start of the PME era and have either been ignored, not been recognised at all, or deemed acceptably low.

  • 0

    RichardCS2:

    So, at a friend's house there is a 6 mm^2 bond to an up-and-over garage door, fitted so far as I can tell when the house was built in 1990. I would expect all the houses on this estate to have them though I haven't checked. Now would anyone like to argue that the risk associated with this large metallic surface with a conductive handle, touched regularly whilst standing on the driveway and connected to a PME-labelled earth terminal is significantly different to the car plugged in on the driveway?




    Is the garage door really an extraneous conductive part? ? 


    Surely the difference is that the door isn't plugged into the mains. I'd remove the bonding.

  • 0
    I don’t think that is the point RICHARD is making. Merely that the door when bonded represents a risk that is often cited for EVs.. Back in the eighties and nineties bonding just about anything that was metal was the message that was perceived by the Hoi-Polloi  if not totally advocated by the oligarchs. I remember heated debates about the bonding of metal window frames and window cleaners on metal ladders dying in their thousands. 

    Regardless of what we as individuals may perceive as risk, the law requires that it is assessed and reduced to a level as low as reasonably possible. To that end we use guidance from relevant authorities so there is no escaping the guidance in BS 7671 for electrical installations or Section 722 of that document and the attendant COPin particular, for EV charging.
  • 0

    gkenyon:

    The separation distances that "keep cropping up" in the case of separation of TT systems (2.5 m, 3.5 m, 10 m) are actually based on Figure 16 in BS 7430.




    Graham, thank you for your opinion above. So I think that I would be all right 'cos the service cable is modern and the old PILC one is a good 10 m away where it runs in company with the probably metal gas pipe and probably plastic water pipe. The gas main in the street is still metal and runs very close to the lamp post and the JB to my property.


    I know all of this 'cos being a nosey sort of character, I was present when holes were dug.


    But what I don't know is what goes on next door, so yes I can see that TT doesn't work for everybody.

  • Former Community Member
    0 Former Community Member
    Yes, I could remove it (and wedge a piece of plastic between the door frame and the gas pipe). My point was more that there are hundreds of these in this estate, and vast numbers of similar situations, many as Lyle points out dating from the "bond everything" era and others an inevitable consequence of normal earthing and bonding practices. There is a logical inconsistency here where we seem to worry deeply about EVs, feel a bit uncomfortable about outside taps and outdoor use of class I appliances, and then proceed to ignore all other TNC-S connected outdoor metalwork. Light switches, gas meters and pipes, electric gates and bollards, garage doors connected via door openers or any other means, most of the caravans on domestic driveways, block heaters, fences with light fittings, etc. The risks are clearly comparable in many cases so either there is a real problem that extends wider than electric cars (and therefore needs dealing with), or the risk associated with EVs is a trivial increase on that which already exists and has been long considered acceptable.


    Perhaps the truth lies between the two, possibly lost neutrals occur rather more often than we are really comfortable with and no-one has really considered the extent of the TNC-S connected outdoor metalwork that exists until prompted by just one more item. Perhaps the whole safety case for TNC-S was too reliant on the rapidly disappearing metallic gas and water mains and assumptions about what equipotential zones could reasonably be created, together with last-century's attitude to risk. One thing stands out though, we don't have a general regulation for not connecting a TNC-S earth to large outdoor lumps of touchable metal, only specific ones for specific lumps of metal that are car or boat shaped. The connection to the garage door is not required, but nor is it prohibited.

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