Earth rod for EV charger

[davelx]

AAUI, the concern here is to have no significant PD between the car and the surface on which it is standing (and insulated from by its tyres). Any significant PD between the car and its surroundings could prove "interesting" for someone who provides a path between the two, for example when they go to open the car door.

As we know, the potential of a TN-C-S CPC can be significantly above that of the surrounding ground, and it is for this reason that the use of a local earth rod connected to the charging point, and isolation from the TN-C-S CPC is needed. The earth rod should really be close to the area on which the vehicle is standing, to minimise PD between the vehicle and the surrounding ground.

I believe the "diagnostic box" contains a DC sensitive RCD. The wall mounted Polar charger I have for my Ampera does, so I don't need an expensive DC sensitive RCD in the CU.

I note that 17th ( 722.411.4.1) specifically states that the regulation "need not be applied for the charging point at a dwelling if none of (i), (ii) or (iii) is reasonably practical"

 

[ban-all-sheds]

Note also that in a little over 10 weeks that "reasonably practicable" get-out goes away.

 

[JohnW2]

AAUI, the concern here is to have no significant PD between the car and the surface on which it is standing (and insulated from by its tyres). Any significant PD between the car and its surroundings could prove "interesting" for someone who provides a path between the two, for example when they go to open the car door.

Indeed so.

As we know, the potential of a TN-C-S CPC can be significantly above that of the surrounding ground, and it is for this reason that the use of a local earth rod connected to the charging point, and isolation from the TN-C-S CPC is needed. The earth rod should really be close to the area on which the vehicle is standing, to minimise PD between the vehicle and the surrounding ground.

Exactly - hence my advice to the OP that that approach [his 'option (c)'] was the safest approach (and probably the only practical compliant approach come next year).

However, as I understand it, the OP was asking about "a device which disconnects everything (including the CPC) in the event of a pd of 70V or more between CPC and 'earth' " as an alternative to TTing the charging point. Apart from anything else, I can't see a lot of point in such an approach. To implement it would require some approximation to a 'true earth' reference which, in practice, I presume would have to be a local earth rod - and, once one has got that, why not just use it to TT the charging point rather than as part of a system for disconnecting the exported 'house earth'?? ... but maybe I am missing something.

Kind Regards, John

 

[davelx]

However, as I understand it, the OP was asking about "a device which disconnects everything (including the CPC) in the event of a pd of 70V or more between CPC and 'earth' " as an alternative to TTing the charging point. Apart from anything else, I can't see a lot of point in such an approach. To implement it would require some approximation to a 'true earth' reference which, in practice, I presume would have to be a local earth rod - and, once one has got that, why not just use it to TT the charging point rather than as part of a system for disconnecting the exported 'house earth'?? ... but maybe I am missing something.

Kind Regards, John

No, I don't think you are missing anything. I think some are perhaps over-thinking this - if they do what you suggest and TT the charge point then all will be fineso long as the earth rod is in close proximity to the vehicle standing.

The 70V disconnect everything requirement is (as I'm sure you know) 722.411.4.1 (iii), which as noted earlier, need not be applied to a dwelling.

 

[JohnW2]

No, I don't think you are missing anything. I think some are perhaps over-thinking this - if they do what you suggest and TT the charge point then all will be fineso long as the earth rod is in close proximity to the vehicle standing.

Quite.

The 70V disconnect everything requirement is (as I'm sure you know) 722.411.4.1 (iii), which as noted earlier, need not be applied to a dwelling.

Indeed, but if I understood correctly what what being said/asked, it seemed as if the OP was contemplating the possibility that such was an alternative to TTing the charging point in a domestic setting - which, as I said, would seem to make little sense to me, even if it were possible.

Kind Regards, John

 

[Les9000]

That device could be in the charging point apparatus.

Does anybody know if any of them have it?

Hi, sorry it has been a few months. As a few people questioned whether the device exists, I have an answer.
I had a PODPoint device supplied & installed last year, subsidised by the £500 government grant.
Installer connected it to my TNCS supply - I objected and demanded a TT install.
I took special interest, being one of the unfortunate few who has had a lost neutral a few years ago due to a failed joint in the road.
Installer called his employers and they claimed exemption quoting the installation guide:
https://s3-eu-west-1.amazonaws.com/podpoint-website/Pod-Point-Solo-Installation-Guide.pdf
They also informed me in an email: "The POD Point we fitted at your property today has a PEN Isolation System in accordance with BS 7671:2018 Reg 722.411.4.1 (iii)".
They don't say how. I struggle to imagine how they do it. Perhaps they are monitoring for L-N voltage dropping below ~180V, as it would if voltage on PEN conductor rose above ~50V; if it does they would then have to isolate L, N, and E from the cable plugged into the car.

 

[SimonH2]

It's there in the document you linked to, page 2 :
The Pod Point Solo features an on-board monitoring system to detect low voltage supplies and potential earth problems, If such a condition is encountered the charge cycle is ended and the vehicle becomes isolated from the incoming supply
These features emit the need for the installation of an earth electrode and the POD Point Solo unit can safely be connected directly to a TN-C-S (PME) earth system without any special arrangements.

 

[JohnW2]

... These features emit the need for the installation of ...

Is that copied/pasted, or is your typing responsible?

Kind Regards, John

 

[SimonH2]

It's copied, not my typo

 

[Les9000]

I checked my paper documentation provided by the supplier/installer.
It is the same as the online document, saying: "These features emit the need for the installation of ...".
Whilst "omit" would make a little more sense than "emit", it doesn't look like good grammar.
Maybe "eliminate the need..." would be better?
It is clear that they are claiming their device is compliant on TNCS.
I still don't like it - I certainly thought about it when I unplugged charge cable from my car whilst standing in a puddle today.
Les.

 

[JohnW2]

I checked my paper documentation provided by the supplier/installer.
It is the same as the online document, saying: "These features emit the need for the installation of ...". ... Whilst "omit" would make a little more sense than "emit", it doesn't look like good grammar. ... Maybe "eliminate the need..." would be better?

Indeed - or something like "avoid the need,..." or "obviate the need ..." - but I suppose that, as you suggest, it's most likely that "eliminate" somehow ended up as "emit" (it does, after all, contain all the 'right' letters, in the right order - just not all of them!), perhaps as the result of a spell-checker or the dreaded 'predictive text'!

It is clear that they are claiming their device is compliant on TNCS.

Yes, that does seem to be the case.

Kind Regards, John