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.

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?

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.

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.

Well then it is the case you have a private substation case or at least a dedicated one, and if TNS is available, then to make use of it is very sensible. Large farms with enough demand to be the sole user and so to command a bit of muscle in negotiations, occasionally do the same, it sidesteps the awkward PME / PEN/ ground lift/ questions entirely.

Of course the cars may well be parked within the near field of the substation electrodes, so even if you hammered more in all that happens is you have something closer to a direct connection, rather than two isolated electrodes connected via "the electrode at the end of the universe", to paraphrase Douglas Adams. You may not have deliberate electrodes but I bet you have conductive parts in contact with the terra-firma to some degree, in the form of mounting posts, the body of the chargers, fences, bollards  etc at least this way they are all at the same voltage.

I won't ask about the substation HV earthing, that is firmly the DNO question.

The other thing to watch for is supplies from other substations entering the area, perhaps for odd streetlamps and so on, but as they cannot share the earthing, these just need to be out of simultaneous reach instead, much as they would for any pair of transformers not explicitly bonded.

Mike.

Electron666 said:

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.

Thank you for the useful context. It wasn't at all clear in the OP.

'and the utility company have confirmed it won't be amended to a TN-C-S in the future'

I thought I'd given a pretty big clue but apologies you found it not 'at all clear'.

Seriously though, thanks for taking the time. I got my answer plus some other useful points to consider.

'and the utility company have confirmed it won't be amended to a TN-C-S in the future'

I thought I'd given a pretty big clue but apologies you found it not 'at all clear'.

Seriously though, thanks for taking the time. I got my answer plus some other useful points to consider.