Yes - there is no longer a credible supply-side condition that could cause the body of the car to float to full mains voltage relative to true earth without some  kind of ADS operation so those requirements do not apply.  It must be said that neither electrode not OPEN detector would do any harm if fitted however.

It must be said that round here to secure such an assurance from a DNO would be unusual, as they are very much in the habit of performing a kind of PME conversion, when neutral and earth get combined, at repairs when TN-S street cables fail. If nothing else it saves them keeping spare reels of both 5 core and 4 core, and makes it easier for them to ensure lower earth impedances/ voltage drops without significant cable replacement. So the advice at least round here for normal domestic situations (Hants) is that it is better to treat TN-S as if it might one day become TNC-s anyway.(Or in reality, to push the nomenclature, perhaps more of a TNS-C-S-s - where the small letters are consumer side and the capitals are what is in the street beneath your feet as you walk along.)

However, if you have a private transformer, then you are in change of the what happens to it, so a TNS system can be guaranteed, then go for it.

Mike.

Confirming that the arrangement will remain TN-S forever and stating that there is no present intention to change it are two very different things.

Thanks

Hi Chris, I was trying to steer any responses away from the reliability of a TN-S arrangement remaining so, which is a conversation of its own. Simply wanted to confirm if a TN-S arrangement was compliant for EVC with no O-PEN devices or earth electrode present. Thanks

Well, if it's TN-S there is no PEN for an O-PEN device. What tells you that the supply is TN-S please?

mapj1 said:

Yes - there is no longer a credible supply-side condition that could cause the body of the car to float to full mains voltage relative to true earth without some  kind of ADS operation so those requirements do not apply.

Except that, just as PEN conductors can "break" over time, so can the protective conductor in a similarly constructed cable for TN-S systems ... and then "leakage" (action of noise filters) - or diverted neutral currents through shared extraneous-conductive-parts with PME installations - could also lead to hazardous touch-voltages and touch-currents. In this case, there would probably not be lights dimming to alert the installation owner, or users ... and the risk is probably less if there are extraneous-conductive-parts and/or fortuitous connection of exposed-conductive-parts with Earth, because hopefully we are talking currents of the order of mA, or a few A, not lots A as with the broken PEN situation.

However, I would agree that Regulation 722.411.4.1 would not apply to a TN-S installation from a private transformer, or (as per the IET Code of Practice) where the DNO has stated it will never be converted to PME.

Electron666 said:

I was trying to steer any responses away from the reliability of a TN-S arrangement remaining so, which is a conversation of its own.

Agreed ... but a criteria to be addressed according to the IET Code of Practice for EV Charging Equipment Installation, which provides what might be considered good practice on the subject.

True - but  a TN-s with a broken cpc tends to become an accidental TT, which then requires additional faults between L and E to become really dangerous - and as car charger installations and more modern wiring generally tend to include RCDs, these second faults are also likely to be detected. The level of adventitious earthing needed to keep the touch voltage to a safe level is really very weak, and likely to be provided by incidental earthed objects, though I do agree there will be corner cases where it is not.

A broken PEN requires no further fault, just some loads connected L-N to become immediately dangerous and an improbably good earth to keep the touch voltage down to a safe level against a large single phase load pulling up.

M.

mapj1 said:

TN-s with a broken cpc tends to become an accidental TT

Usually ... but only if there are extraneous-conductive-parts. A modern domestic installation may have no extraneous-conductive-parts.

mapj1 said:

which then requires additional faults between L and E to become really dangerous - and as car charger installations and more modern wiring generally tend to include RCDs, these second faults are also likely to be detected.

Some "faults" are built into many items of equipment in Class Y capacitors ... and the "leakage" is low enough on each circuit not to operate the RCDs, but will sum in the interconnected protective conductors, waiting for the the conductive element (person) eventually providing the connection with Earth. Most of the time, leakage in domestic installations isn't a worry ... but if more than one installation is downstream of the break in the protective conductor, who knows?

mapj1 said:

The level of adventitious earthing needed to keep the touch voltage to a safe level is really very weak, and likely to be provided by incidental earthed objects, though I do agree there will be corner cases where it is not.

Agreed.

mapj1 said:

A broken PEN requires no further fault, just some loads connected L-N to become immediately dangerous and an improbably good earth to keep the touch voltage down to a safe level against a large single phase load pulling up.

I think I've illustrated a mechanism above by which a broken PE in the distribution may give rise to immediate hazardous touch currents in some domestic installations.

I think it goes to show that there are compromises and issues with the three common earthing arrangements in the public distribution networks.

Thanks for all the responses.

The situation is that the end client has various sites around the country and uses the same utility company to procure a sub themselves within the site boundary and insists on getting a TN-S earth each time. The capacity of the transformer is taken up by the client's agreed supply capacity, so although not a private sub, no other customers or installation will be fed from it unless the client reduces their ASC, which won't happen. I can find a lot of guidance advising we should work on the basis that, for EV, a TN-S may become a TN-C-S in the future which I understand, but couldn't find anything much about actually earthing a EVC point in the case of a TN-S. I was informed that the price received for O-PEN devices was not feasible and earth electrodes were not wanted due to many underground services and metallic street furniture etc that will be ground mounted and added to in the future. 

I'm not in control of the the EV products being installed or the finances, simply to confirm that the earthing method is compliant. The client and utility company are all aware that there is electric vehicle charging present, that relies on the TN-S being permanent. I have asked for written confirmation from the utility company that the TN-S will remain which will be kept with the elec installation certs and also requested labelling on the utility equipment, if possible.