I'm told this is against regulations?

[Simlec]

Agree with that.
If source is PME then it needs to be TT if it's mounted outside a building. This is also dependent on your own risk assessment providing evidence there are no simultaneously accessible extraneous parts belonging to the PME system.
There is currently a "get-out" which allows use of PME "if not reasonably practicable". I suspect that is being used more than sensible by many EV charger installers. This also relies on a credible risk assessment (your neck being on the line in the court) to say that's all OK for whatever reasons you choose. The latter get-out will disappear completely in 18th as I believe.
And don't forget that the TT earth you provide needs to be LOW. Chargers (certainly 32A ones) will monitor EFLI and not allow charge if it's too high. Notionally 200 ohms, but don't believe it. I have it on good authority from a Renault tech that their chargers might need as low as 70 Ohms to operate reliably. - That is likely to need more than a 4' twig in the soil.
And don't forget type A RCD and probably a D type breaker.

I think you need to do some reading too

 

[1Justin]

By all means. I have the Code of Practice. Point me in the direction if stuff I put down there is wrong. I'm happy to be better informed

 

[Simlec]

page 26
its also in your bs7671 page 279
Why make it all TT when you can just connect the rod to the MET like i think they are asking in the 18th

 

[1Justin]

But doesn't this need an impractically (for cheapo domestic install) low electrode resistance to achieve the 70V limit?

 

[Simlec]

It says that if you can't meet the requirements you can still use TN system if its a dwelling. The code of practice goes on to say that there are way to help reduce the touch voltage as getting the required low Ra is unlikely. I'm not saying it does not happen but how many open circuit PEN installations have you been to?

 

[1Justin]

It does, and I have needed to do that when moving a charger. (Lots of very sandy dry soil near here). I believe that it won't allow that any more in 18th edition.

 

[Simlec]

Well the risks are only going to get worse with more chargers installed.

 

[DPG]

It says that if you can't meet the requirements you can still use TN system if its a dwelling. The code of practice goes on to say that there are way to help reduce the touch voltage as getting the required low Ra is unlikely. I'm not saying it does not happen but how many open circuit PEN installations have you been to?

There have been two open circuit PEN conductors on our estate alone. Both were faults in the joint boxes (installed circa 1974) underneath the pavement feeding the houses. In fact, one was at my house and resulted in my wife receiving a shock from the metal-clad lightswitch in the garage. Never assume it can't happen - there are a hell of a lot of those joint boxes out there.

Oh and they came out pretty quickly to the fault! They fitted a temporary bit of concentric from my neighbours cut-out across the drive to mine. Proper job - it had sticky tape holding it down and everything

 

[Rpa07]

What was your wife doing in the garage @DPG - you want to be careful there, next thing you know they’ll be driving!

 

[DPG]

What was your wife doing in the garage @DPG - you want to be careful there, next thing you know they’ll be driving!

It's a scary world!