DNOs forbid PME earth being exported???

[Pretty Mouth]

I would put PME down as a C2 on an EICR if I saw that it was taken outside.

So, a metal outside tap, connected to the inside bonded pipework - C2?
An outside class 1 light fitting - C2?
A wooden summer house, wooden floor, no extraneous parts, with a double socket and a light in it - C2?

What regulations would you reference to justify these codes?

 

[Deleted member 122525]

Look on the ITE website,
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You guys sound dangerous, glad you don’t work with me or around me,

 

[westward10]

Look on the ITE website,
[automerge]1574632328[/automerge]
You guys sound dangerous, glad you don’t work with me or around me,

Not sure who the ITE are but insulting other members without sound technical reasoning is not the way forward.

 

[Deleted member 122525]

This is one of the worse, forums I have ever joined, the lack of knowledge and understanding here is unreal, everyone seams to be trying to take a short cut to getting work done.
I don’t really give a ---- what people think. My knowledge and understanding is sound, and my work is safe, I don’t ever take risks, and it is my opinion and I don’t have to justify a single thing to anyone here,

 

[Pretty Mouth]

Well, he's not here anymore to defend himself, but he kind of shows why I started this thread in the first place.

I'm on a FB group for sparks trained through a certain centre, most members are relatively new entrants to the industry such as myself, but some old (and apparently very knowledgeable) hands as well. The prevailing attitude in the group is "for outbuildings, DNO forbids TN-C-S, must TT it", which as you've probably gathered I disagree with. When I challenge this, at best I get referred to the professional electrician article I tried to link to in the first post, at worst I just get it repeated slightly more firmly.

It's not just in that group, I see it all over the internet too.

 

[Dan]

I think you'll always get plonkers in trades and on forums. It's life.

But you can hold your head up high if you crack on and do the job right.

If it's 'the done thing' it doesn't mean it's right.

 

[Cid]

The regs do say you can't install a car charging point outside with exported PME.

From that we can infer we shouldn't be taking PME outside. Perhaps?

 

[Simon47]

My knowledge and understanding is sound, ... I don’t have to justify a single thing to anyone here,

Lets examine the facts. You've made (bkanket) statements that other people who understand the issues didagree with (professionally). You've failed to provide any reasonable justification as to why your professional opinion is more valid than anyone else. You've also failed to provide any references to back up your position.
You then resort to insults, and an "I know thus stuff" attitude rather than answer reasonable questions.
I've made my mind up what sort of sparky you are - not one I'd employ ! Others can make their own minds up.

The regs do say you can't install a car charging point outside with exported PME.
From that we can infer we shouldn't be taking PME outside. Perhaps?

It's not that simple - and you can use an exported PME earth with the right considerations. In fact, the limitations are such that few will be able to use a TT earth and must use the PME earth.
It's interesting to observe that for a long time the rules has been "thou shalt not switch the protective earth, ever", yet now we have a subset where the earth must be switched

 

[Pretty Mouth]

The regs do say you can't install a car charging point outside with exported PME.

From that we can infer we shouldn't be taking PME outside. Perhaps?

TBH I don't know enough about EV chargers to say exactly why PME isn't allowed. At a guess I would assume the same reason as caravans - a large metal object that is touched frequently by people standing on bare ground. If you lose the dno neutral the odds of someone getting a shock are high.

Compare that to a wooden summer house, wooden insulating floor, no extraneous parts. The risk here is no higher than in the main building, possibly less.

Assess on a case by case basis

 

[EddieSparks]

It is mainly for the risk of open circuits as I understand it, Regarding EV charging sockets. I was always told PME outside was risky mainly due to the possibility of the potential difference between the supply earth and the general mass of earth. Due to the volt drop if the run is long, from the transformer to the out building, but a risk assessment is always the best way to go,

 

[davesparks]

“Suppose you TT an outbuilding, bonding the extraneous metal water pipe that originates (and so is bonded) in the main, TN-C-S supplied building. If we lose the DNO neutral, that pipe is going live along its length, both in the main building and the outbuilding, along with everything else bonded/earthed out there. Now we have the worst of both earthing arrangements, doubling the risk.”

That’s assuming that you are taking a metal pipe out there, and not poly, so in that case you would precautions to not let this happen.
The main reason why I am so strong for not taking PME outside, is when I did my 18th update, I was taking to an engineer who works for SSE, his job is to locate and fix, floating neutral faults on PME supply cables, he was very knowledgeable about this supply type. He could not state enough how dangerous it is under fault conditions, he even went on to say if his house had a PME supply, he would disconnect it and make his house TT.
I was also taught this when I was doing my 2330 lev3, my NVQ3 and my inspection and test.
I would put PME down as a C2 on an EICR if I saw that it was taken outside.

You cannot code an observation on an EICR based on your opinion, you can only code it according to bs7671. Currently there is nothing in bs7671 to support your suggestion of a C2 for a PME earth used for an outbuilding.

Yes PME has its downsides, but it is a very reliable earth connection for the vast majority of the time. You talk about it as if supplies to installations suffer neutral faults on a regular basis, they don't.

 

[Simon47]

You could always add your own earth rod, so if there's a PEN failure you can earth the whole street
Wasn't there talk of that being made mandatory in the last update to the regs ?

 

[DPG]

You could always add your own earth rod, so if there's a PEN failure you can earth the whole street
Wasn't there talk of that being made mandatory in the last update to the regs ?

I think it got removed luckily.

 

[EddieSparks]

Not totally removed, I found this the other day in the OSG chapter 4.

 

[davesparks]

You could always add your own earth rod, so if there's a PEN failure you can earth the whole street
Wasn't there talk of that being made mandatory in the last update to the regs ?

Yes you can, that's how it's done in a lot of other countries and is a good thing in my opinion.
It was going to be included in the 18th but I think it has been delayed for an ammendment.
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The regs do say you can't install a car charging point outside with exported PME.

From that we can infer we shouldn't be taking PME outside. Perhaps?

The regs don't say this at all, they have certain requirements for car chargers connected to a PME supply.