TT system.

[sparkytim]

This is getting boring, why not just move on and agree to disagree and not go over the same old ground every time someone mentions PME.

headbang

 

[ianmacd]

This is supposed to be a forum with proffessionals on. To that end I would expect them to use the correct terms. PME is not the same as TN-C-S.

 

[Chr!s]

Spin

The definition states that TN-C-S is also known as PME.?

The usual formof a tn-c-s system is as shown, where the supply is TN-C and the arrangement in the installation is TN-S.

This type of distribution is also known as pme, the system pen is earthed at two or more points, which it shows in the illustration above.

Though as metioned before there are two basic forms of TN-C-S

TN-C-S system with pme

TN-C-S system with pnb(protective neutral bonding

There is no illustration in bs7671 for TN-C-S pnb, the main difference being the pen is connected to earth at one point only.

Now i do agree with spin that TN-C-S pme is how the majority of TN-C-S supplys are distributed.

Andy

not fully... CNE 'could' be used to describe PME, in that both use neutral for the earth

only PME is used for general distribution, as CNE only has 1 rod at star point. CNE may be used when a place has its own transformer?

Cne (combined neutal earth)/ (pen( Protective earth and neutral)

Cne is used to describe a pen conductor and vice versa not Pme

What your describing is TN-C-S (pnb)

Regards chris

 

[spinlondon]

Here's an excerpt from Western Power's description of types of earthing:

"Protective Multiple Earthing (PME)

PME, known as TN-C-S within BS7671 (Requirements for Electrical Installations, IEE Wiring Regulations) is the most common form of earthing provided at new installations. We utilise a single conductor for neutral and earthing functions and provide an earth terminal at the customer

 

[ianmacd]

And then you jump on spouting the same rubbish too. Its a never ending loop.

So again I will ask. If you have a TN-C-S presentation distributed on a PME network and you remove the supplied Earth and use a rod, what is that? Still TN-C-S because the network is still PME?

 

[Chr!s]

Spin

As far as I can see, it is accepted accross virtually the whole industry that TN-C-S is PME. The very few people who don't accept this are the members of this forum who insist on making irrelevant posts whenever someone makes the assumption that TN-C-S is PME.

I don't think people are arguing that virtually all tn-c-s will incorporate pme, but lets not be ignorant to the fact that out there, their is also tn-c-s-pnb.

I am also aware that many suppliers do not offer tn-c-s pnb, but thats not to say you wont come across it.

BS 7375 code of practice for distribution of electricity on construction and building. read it, it clearly defines :

A TN-C-S system (incorporating PME) cannot normally

be used as it is not practicable to ensure that all

extraneous-conductive-parts, either existing or added

during construction, are adequately bonded at all

times.

Question spin. In the above is tn-c-s (pnb) acceptable

BS 7430 code for earthing also recognises tn-c-s(pnb).

People are not disagreeing to the fact that tn-c-s is virtually all pme we are just saying Tn-c-s comes in two basic forms and that pme is used to express that there are two or more connections to earth on the pen/cne.

regards chris

www.eon-uk.com/distribution/CiCdocs/01%20Technical%20Documents/CN%20East/East%20Earthing%20Manual%20Feb%202002.pdf

look at page 77 - 78

 

[ADS]

The multiple thanks are because both Plumber and Spin are making valid points backed up by technical references - which is all I ask.

Bottom line - Most people refer to TN-C-S as PME and vice-versa, because this is the most common format of distribution and installation - as Spin points out, even the 'Regs' and other reference documents refer to them as one and the same.

As Plumber and myself pointed out, TN-C-S can be supplied by PNB, but not as common, so rarely referred to.

 

[ianmacd]

I guess its akin to calling a vacuum cleaner a hoover. In the old days I guess most of them were hoovers but that doesn't make it any more correct. If this was not a forum of professional sparks then it would not be such a big deal but it is and we should know better than making generalising statements.

 

[Sidewinder]

I could not post this as a post so I hope the txt file is OK.

I don't know what the formatting will look like.

Sorry.

TNC-s Vs PME.txt

 

[ADS]

Interesting, to say the least

 

[steptoe]

I could not post this as a post so I hope the txt file is OK.I don't know what the formatting will look like.

Sorry.

I cant open it.

 

[Sidewinder]

Sorry Steps, it's just a plain text file, it should open with Windows notepad or any word processing type application. It opens for me, but that would be expected as I created it and posted it!

 

[ianmacd]

It did open for me too.

 

[steptoe]

Sorry Steps, it's just a plain text file, it should open with Windows notepad or any word processing type application. It opens for me, but that would be expected as I created it and posted it!

got it, I downloaded and saved, rather than try to open it on the fly(as such).

opened OK now, just reading.

 

[steptoe]

very interesting read,

so if my understanding of this is correct,

then (in the UK):-

DNO is now legally required to always make a TNCS a PME system.

DNO is NO longer required to notify(label) such a system as PME.

if a TNCS is NOT PME I can take DNO to court as they have broken the law.

 

[Sidewinder]

very interesting read,so if my understanding of this is correct,

then (in the UK):-

DNO is now legally required to always make a TNCS a PME system.

Yes

DNO is NO longer required to notify(label) such a system as PME.

Not from the information I could find

if a TNCS is NOT PME I can take DNO to court as they have broken the law.

No that would be down to the CPS or another Crown body as this is Statute law, not Civil / case law

My Red.

 

[steptoe]

Quote:

Originally Posted by steptoe View Post

very interesting read,

so if my understanding of this is correct,

then (in the UK):-

DNO is now legally required to always make a TNCS a PME system.

Yes

DNO is NO longer required to notify(label) such a system as PME.

Not from the information I could find

if a TNCS is NOT PME I can take DNO to court as they have broken the law.

No that would be down to the CPS or another Crown body as this is Statute law, not Civil / case law

My Red.

My Red.

so,

for all intents and purposes we still have to treat TNCS as NOT PME then.?

 

[Sidewinder]

No not really Steps as the DNO's are legally bound to PME all TN-C-S supplies, labelled or not.

I'd have to check the legal requirements for labelling, I did not do this.

Their "trade" body now requires that all new supplies are CNE thus TN-C.

 

[steptoe]

No not really Steps as the DNO's are legally bound to PME all TN-C-S supplies, labelled or not.I'd have to check the legal requirements for labelling, I did not do this.

Their "trade" body now requires that all new supplies are CNE thus TN-C.

I understand sidewinder,

but,

NOT all TNCS systems seem to be PME,

not least of all by the Ze/Ra readings anyway, and now that (it doesnt seem to be a requirement) no PME labels are provided its hard to tell.

I honestly fail to understand how a standard TNCS system can overnight magically become PME just because the law changed.

did anyone notice the DNO digging up all their joints to rod them?

does anyone on here have TNCS with a rod just outside their house where the cable comes in?

I really have a lot of doubts as to the validity of all this, and as its not a civil law then basically we dont have a cat in hells chance of ever winning any court case where this may be involved, Im still going to err on the side of safety and keeping my ass outta jail and assume TNCS is NOT PME unless I specifically have it in writing

EDIT

is this a retrospective law?

 

[Sidewinder]

It has been in place for over 8 years now.

It will have certain retrospective requirements, but these are not easy to find.

Any new supply installed in the last 8 yrs that has a CNE/TN-C distribution must by law be PME.

No hard evidence on the PME labels, YET!

The issue is NOT really TN-C-S it is more the TN-C & CNE LV distribution networks.

There is no legal requirement to rod every joint, just to undertake to ensure that the connections are sufficiently robust effectively.

Why would you wish it to be civil law, in civil law the onus would be on you to undertake the prosecution, in Statute law the requirement is on the State.

Similar to, please excuse the shocking parallel, if you were stabbed in the street, you would not necessarily try to prosecute the person who stabbed you. The Crown would undertake the first prosecution for say ABH, if this was successful, this could then open the flood gates for you to undertake a civil prosecution for damages etc.

Please remember:

Criminal law = Punisment

Civil law = Compensation

There would be no requirement for you to win a court case would there, I can't see the requirement. Please explain?

As for the validity, my post is based on published Statute law, so the validity does not need to be proved, it is there in black & white so to speak.

Akin to speeding, theft, criminal damage or physical assault which are all "offences" under criminal law.

Civil or case law is compensation "based", this is a different kettle of fish.

Or at least that is what I was taught when I studied these aspects.

BTW, Late now, sorry, :good night: