Can 'the same earthing system' described in Regulation 411.3.1.1 be satisfied if both supplies originate from the same DNO PME cable in the street

I guess in most cases they will be - so the chances of harm are pretty low. Justifying that could be a lot more interesting - not only in a few cases will they not be on the same cable originally, there's no guarantee that things will remain the same into the future. (Shades of having to treat TN-S as PME in case the DNO change things later). I've seen situations where a DNO has cut an existing cable and fed some properties from the opposite end (from a different substation) to adjust things when demand increased due to a new development elsewhere (I got to know after we weren't told that planned work would cut our power - seemingly their records didn't have the location of the cut & re-route in quite the right place, so they thought we were on the other side and shouldn't have been affected).

I guess that open-PEN devices should mitigate the risks somewhat - as if either PE drifts too far away from true Earth at least one of the car should be disconnected from PE & left to float (notwithstanding that the devices won't detect all hazardous conditions and disconnection times in the region of 5s aren't entirely aligned with the usual ADS requirements, so won't help where one installation experiences a L-PE fault - but arguably we have that problem with unbonded extraneous-conductive-parts outdoors anyway).

Does 722.413.1.2 solve the problem?

Maybe. If you could guarantee that the vehicle side was genuinely earth free. I don't see much of an appetite for 7kVA/22kVA transformers though and there are still a lot of unanswered questions about the A722 approach altogether (e.g. actually meeting section 413 requirements). Has anyone ever seen that implemented?

   - Andy.

Can 'the same earthing system' described in Regulation 411.3.1.1 be satisfied if both supplies originate from the same DNO PME cable in the street

I guess in most cases they will be - so the chances of harm are pretty low. Justifying that could be a lot more interesting - not only in a few cases will they not be on the same cable originally, there's no guarantee that things will remain the same into the future. (Shades of having to treat TN-S as PME in case the DNO change things later). I've seen situations where a DNO has cut an existing cable and fed some properties from the opposite end (from a different substation) to adjust things when demand increased due to a new development elsewhere (I got to know after we weren't told that planned work would cut our power - seemingly their records didn't have the location of the cut & re-route in quite the right place, so they thought we were on the other side and shouldn't have been affected).

I guess that open-PEN devices should mitigate the risks somewhat - as if either PE drifts too far away from true Earth at least one of the car should be disconnected from PE & left to float (notwithstanding that the devices won't detect all hazardous conditions and disconnection times in the region of 5s aren't entirely aligned with the usual ADS requirements, so won't help where one installation experiences a L-PE fault - but arguably we have that problem with unbonded extraneous-conductive-parts outdoors anyway).

Does 722.413.1.2 solve the problem?

Maybe. If you could guarantee that the vehicle side was genuinely earth free. I don't see much of an appetite for 7kVA/22kVA transformers though and there are still a lot of unanswered questions about the A722 approach altogether (e.g. actually meeting section 413 requirements). Has anyone ever seen that implemented?

   - Andy.

Hi Andy,

The 'new developments' is where we are going to have the issues. A number of these do not have off street parking but rather have dedicated parking space's elsewhere on the development which could be a distance away from their house/apartment and are mostly directly side by side with others parking spaces. 

We have been asked to look at one at the moment which requires 70 x 7kW chargers through out the development with none of them attached directly to the houses. We will therefor require a number of metered supplies located in feeder pillars through out and supply a number of chargers from each. 

I assume therefor to comply with 411.3.1.1, and where we are using PEN fault protection on a PME DNO supply, we would require any metal lamp post within touching distance to be from the same feeder pillar and DNO cut-out as the car on charge? As the lamp post are going to be located next to the parking bays, adopting a TT earthing system for the chargers is not really an option.

Regards

Mark

Mark Fleming said:

The 'new developments' is where we are going to have the issues.

There should be no issues with open pen on a new development. If there are, sue the pants of the DNO! 
If they can’t guarantee the integrity of their network on a new development then they should dump the PME. 
However, no issues on new estates in Ireland which are always TNCS. It seems it’s only in the U.K. where folk get their knickers in a twist at the mere mention of EV and PME!