Earthing system??? Concerned

[bartkusal]

Hi guys, need some opinions from big boys. I will try to be short as possible.
I was helping on big rewire the other month for the well-respected electrician mate. On tests before the job the Ze was 6.7 ohmson TNS supply, so the guy called the other mate who works for DNO as the head needed moving anyway.
So when it got moved they just taped the earth from the heads Neutral terminal as you expectto see on TN-C-S systems, and got it down to 0.22 ohms. I asked them how that is compliant and possible,because you are not sure if the PME system is available, as far as I know the PME’s neutral is earthed every say 4[SUP]th[/SUP] overhead pylon or so and on TNS is just that, Neutral goes straight to substation transformers centre point.
The answer from the DNO guy was, “IT’S ALL B*****KS about all these different earthing systems you on about, every supply is now PME’d and that’s how we do it if this sort of problem arises.”
I looked concerned to my mate and, he said yes, don’t worry that’s how it is, we always done that.
So please enlighten me if that’s the case, otherwise what is the point of brain braking if there is such an easy solution to the problem.

Thanks in advance for replies

Al

 

[somersetsparks]

Hi guys, need some opinions from big boys. I will try to beshort as possible.
I was helping onbig rewire the other month for the well-respected electrician mate. On tests before the job the Ze was 6.7 ohmson TNS supply, so the guy called the other mate who works for DNO as the head needed moving anyway.
So when it gotmoved they just taped the earth from the heads Neutral terminal as you expectto see on TN-C-S systems, and got it down to 0.22 ohms. I asked them how that is compliant and possible,because you are not sure if the PME system is available, as far as I know thePME’s neutral is earthed every say 4[SUP]th[/SUP] overhead pylon or so and onTNS is just that, Neutral goes straight to substation transformers centre point.
The answer fromthe DNO guy was, “IT’S ALL B*****KS about all these different earthing systems youon about, every supply is now PME’d and that’s how we do it if this sort ofproblem arises.”
I looked concernedto my mate and, he said yes, don’t worry that’s how it is, we always done that.
So please enlighten me if that’s the case, otherwise what isthe point of brain braking if there is such an easy solution to the problem.

Thanks in advance for replies

Al

In our area, the DNO know every street and which ones are suitable for PME connection which is nearly all of them these days every joint on that supply cable done in the last 20 or so years will have been 'PME'D'.

 

[somersetsparks]

Be aware though that you can't just stick your earth into the neutral on every TNS supply, only after asking your local DNO and confirming! Years ago they would have been true TNS not anymore!

 

[bartkusal]

Thanks for that, its news to me, but they never contacted anyone, and the guy from DNO worked unofficially, just helping out the mate. On the other hand he new for sure from experience that PME is available, and who cares to ask then I suppose...

 

[chrish_1977]

Welcome to the world of dno's, law unto themselves sometimes

 

[GLENNSPARK]

Welcome to the world of dno's, law unto themselves sometimes

and who`s property is the cutout & associated equipment?

 

[bartkusal]

Be aware though that you can't just stick your earth into the neutral on every TNS supply, only after asking your local DNO and confirming! Years ago they would have been true TNS not anymore!

But it does not make sense anymore, so basically we have to treat all installations as TNCS supplies, are we? All that lost neutrals and exported earth and all that???

 

[GLENNSPARK]

But it does not make sense anymore, so basically we have to treat all installations as TNCS supplies, are we? All that lost neutrals and exported earth and all that???

if the Ze is high.....you ring the DNO and get them to sort it....its their equipment, their earthing facility and their problem....
when you ring them....ask to be put straight on to the duty engineer.....not `stupid bint` on the end of the phone....

 

[bartkusal]

if the Ze is high.....you ring the DNO and get them to sort it....its their equipment, their earthing facility and their problem....
when you ring them....ask to be put straight on to the duty engineer.....not `stupid bint` on the end of the phone....

I grasped all that ages ago Glen, but my point is that it seems we have to treat all installs as TNCS with all the associated issues, even if you think its TNS, because its most probably been PME'd???

 

[GLENNSPARK]

I grasped all that ages ago Glen, but my point is that it seems we have to treat all installs as TNCS with all the associated issues, even if you think its TNS, because its most probably been PME'd???

your PFC will confirm what cant be verified by visual...

 

[johnboy6083]

I tend to agree. I'm currently at college (HNC) with a few jointers from our DNO. One I spoke to didn't understand the difference between the earthing systems, and didnt understand Ze ect either.

he said that 99% of the time, they earth the neutral at every joint.

 

[Phoenix]

At the end of the day, though, if you convert a dwelling to TNC-S from TNS and that then developes a fault which energises the Neutral which the DNO engineers are happily working on (chances are low, I know), you will be responsible. As far as I'm concerned, anything south of the tails is down to the DNO. And that's the way it should be.

 

[Engineer54]

Let me state this very clearly, What has been stated above, about every DNO cable joint being Neutral Earthed is just pie in the sky wishful thinking, unless they are talking about new cable installs!! I'm sure every one of you here, knows the street that they have lived on, (especially those that have lived in the same street for several years)!! So how many of you have seen the DNO dig up sections of YOUR street to PME all the older TN-S cable joints, either all at the same time, or over several years?? ....Let me answer that one for you, very, very, few of you!!

Most of the older TN-S cable lines have only been partly converted, and normally only in certain sections where the ground conditions for one reason or another being overly corrosive to the armouring and sheaths.... Most older cable DNO distribution cables carry both TN-S and TNC-S. And contrary to what many will tell you, not all of the DNO local distribution cables have been converted in any way shape or form. In the majority of cases, the only True DNO PME supplies are the new and converted overhead distribution systems, for the obvious reason, it's simpler and far cheaper, than digging up streets to get to the many underground joints


Why would anyone would listen, let alone believe, what two electricians Mates has to say?? Especially one that is prepared to make an unlawful and unofficial PME connection, and the other supports him!!

 

[Knobhead]

I tend to agree. I'm currently at college (HNC) with a few jointers from our DNO. One I spoke to didn't understand the difference between the earthing systems, and didnt understand Ze ect either.

he said that 99% of the time, they earth the neutral at every joint.

LV jointers on a HNC course?
Most LV jointers I’ve come across are on a par with pond life.

Skilled yes, theoretical no. Most of them it takes 10 minutes to think “I’m getting a shock.”

 

[bartkusal]

Let me state this very clearly, What has been stated above, about every DNO cable joint being Neutral Earthed is just pie in the sky wishful thinking, unless they are talking about new cable installs!! I'm sure every one of you here, knows the street that they have lived on, (especially those that have lived in the same street for several years)!! So how many of you have seen the DNO dig up sections of YOUR street to PME all the older TN-S cable joints, either all at the same time, or over several years?? ....Let me answer that one for you, very, very, few of you!!

Most of the older TN-S cable lines have only been partly converted, and normally only in certain sections where the ground conditions for one reason or another being overly corrosive to the armouring and sheaths.... Most older cable DNO distribution cables carry both TN-S and TNC-S. And contrary to what many will tell you, not all of the DNO local distribution cables have been converted in any way shape or form. In the majority of cases, the only True DNO PME supplies are the new and converted overhead distribution systems, for the obvious reason, it's simpler and far cheaper, than digging up streets to get to the many underground joints


Why would anyone would listen, let alone believe, what two electricians Mates has to say?? Especially one that is prepared to make an unlawful and unofficial PME connection, and the other supports him!!

Thanks, once again very useful peace of information from the top man, that's even better, basically business as usual regards this sort of issues.