High Impedance Earth, advice

[Lareon]

Hi guys,

Just want some advice really.

I had a car charger installed on monday (attempted install)
as the installer was about to wire it up he seemed confused and started saying he couldn't find an earth to my house. after doing some tests on the plug sockets in the house he did some tests and found the resistance was around 2.7k ohms. he stated that it had to be below 200 to fit the unit and told me to ring the DNO, then packed up and left without connecting the unit.

I'll take a picture but after looking around i found what I think has been used as the earth. a piece of flex wired directly into the consumer board and clamped onto a piece of copper pipe that has been buried into the concrete subfloor


I rang the DNO and they said the electrician should have taken a reading from the cutout and they couldn't do anything until he does that.

well he had long gone by that time.

my question is do i just get a copper stake bury it outside, run some 16mm earth to an earthing box and then into the consumer unit.

or do i need to do this by the book and get someone in?

 

[Iggifer]

It would be worth ringing up the DNO and asking if they can provide you with an earth. Probably will be PME if you haven’t got one already.

Are you particularly rural/have an overhead supply?

If they can provide you with PME that’s a better option than fitting a rod. It will probably cost you a fee but likely not a huge amount if they can do it

 

[aptsys]

It would be worth ringing up the DNO and asking if they can provide you with an earth. Probably will be PME if you haven’t got one already.

Are you particularly rural/have an overhead supply?

If they can provide you with PME that’s a better option than fitting a rod. It will probably cost you a fee but likely not a huge amount if they can do it

PME better than a rod?

PME for an external car charger?

 

[John D v2.0]

Take a photo of the intake and meter area and post it here.
Also the pipe that you saw with the cable.
I should hope car chargers are not class I so pme shouldn't be an issue. Cars are probably not extraneous conductive parts!

 

[John D v2.0]

my question is do i just get a copper stake bury it outside, run some 16mm earth to an earthing box and then into the consumer unit.

And test the RCDs trip time at 0.5In and 1In, check all circuits are correctly RCD protected, and check the rod impedance. Then if you want to do it properly fill in the certificate and get the council to inspect.
What's an earthing box? Should be one wire all the way from the rod to the met.

 

[aptsys]

COP suggests that a PME TN-C-S supply shouldn't be used unless the vehicle and charger are under cover of a garage etc. There are some additional statements in the most recent amendment but we do not have enough information to determine the criteria.

 

[Iggifer]

PME better than a rod?

PME for an external car charger?

PME for the rest of his installation. The fitter will fit a rod. The most important thing is getting a decent earth path for his house first

 

[ban-all-sheds]

Cars are probably not extraneous conductive parts!

Are we sure that none of them are ever exposed-conductive-parts whilst charging?

 

[JohnW2]

I should hope car chargers are not class I so pme shouldn't be an issue.

It's probably more of a question of whether the outputs are isolated from earth. Given the advice (regulations?) not to use PME earths, one has to wonder.

Kind Regards, John

 

[JohnW2]

Are you particularly rural/have an overhead supply?

I don't really know why, but I always assumed that the reason I had a TT installation was because my supply was overhead. However, when I was told that I could have TN-C-S if I wanted it, I had to ask myself "Why not?" - and couldn't think of any answer. Overhead TN-S would presumably not be possible, but there's no reason why one can't have TN-C-S.

Kind Regards, John

 

[Lareon]

Yeah I'm quite rural and the building is very old.
I did ring the dno and they said they wouldn't do anything until a reading was taken from the cutout.

I'll take a picture of the setup when i get home tonight for clarification for everybody.

 

[Iggifer]

I don't really know why, but I always assumed that the reason I had a TT installation was because my supply was overhead. However, when I was told that I could have TN-C-S if I wanted it, I had to ask myself "Why not?" - and couldn't think of any answer. Overhead TN-S would presumably not be possible, but there's no reason why one can't have TN-C-S.

Kind Regards, John

They won’t do it on all overhead supplies. At least WPD won’t. Must be to do with how that section of the network is configured but we’ve had them say no on a few overheads and yes on others.

But if it’s available and I had TT I’d bite their hand off

 

[JohnW2]

They won’t do it on all overhead supplies. At least WPD won’t. Must be to do with how that section of the network is configured but we’ve had them say no on a few overheads and yes on others.

Interesting. It was actually WPD who said I could have it.

I presume that, regardless of whether it is overhead or underground, the primary consdieration has to be whether or not it had yet been "PME'd". It looks to me as if there is an earth at the pole which supplies my house (there's certainly some cable which comes down the pole under some 'capping') - and, given that we've been told (to my surprise and 'shock'!) that M=2 is adequate for PME, that ought to be adequate

But if it’s available and I had TT I’d bite their hand off

I have to say that, after thanking them for their 'offer', I told then what they could do with their 'PME earth'

Kind Regards, John

 

[John D v2.0]

Well, m anything is a bonus really, to be honest with pme you've got great ads but you're relying on your equipotential zone having a crisp line to remove touch voltages, however the m will hopefully reduce touch voltages. and with tt you're relying on a working RCD to do the same. Depends which you trust note

 

[JohnW2]

Well, m anything is a bonus really, to be honest with pme you've got great ads but you're relying on your equipotential zone having a crisp line to remove touch voltages, however the m will hopefully reduce touch voltages ....

Particularly given (as westie told us) M is commonly only 2 (one earth at tranny and the other at the end of the main), I presume the main idea is to give some degree of 'security' that one hopefully won't lose one's earth completely (although that can obviously happen with a fault in the branch supplying one, or a few, properties), rather than to reduce Ze and thereby reduce touch voltages.

.... and with tt you're relying on a working RCD to do the same. Depends which you trust note

With TT, touch voltages are usually very high, and RCDs can obviously do nothing to reduce them, but the RCD will hopefully make them go away very quickly. Given that everything in my installation is 'dual-RCD protected' (albeit the 'secondary' RCD is delayed by 100ms or whatever), I'm pretty comfortable. In any event, I spent the first 35 or so years of my life living with TT installations without any RCD (or even VOELCB) protection, and appear to have survived that experience

Kind Regards, John