TT system.

[spinlondon]

This may be clearer. All motorcycles have 2 wheels therefore all 2 wheel vehicles are motorcycles.

That assumption is incorrect is it not?

Just because that section you mention (9(1)) applies to all presentations that are both PME supplied and TN-C-S presented, it does not logically follow that all TN-C-S are PME in the same way you can not say that all PME supplies are TN-C-S presented as they can be TN-S, TT or something else.

Is that clearer?

Bad analogy, as some motorcycles have 3 wheels.

 

[ianmacd]

Or try this:

A Venn Diagram:

A is PME distribution

B is TN-C-S presentation

A & B is the equivelent of Section 9(1).

 

[ianmacd]

The heading is: "Protective Multiple Earthing."The Regulation starts by informing when it applies, ie. where the neutral and earthing functions are combined.

If you look at other Regulations, ie. (5) Inspection of Networks.

This particular Regulation requires that inspections are carried out, and that records of those inspections are kept.

Using your logic, if no inspections are carried out, the Regulation does not apply.

Yes that could be read that way you are correct. But if someone inspected anything then that section would apply. So section 5 only does not apply until the first time you inspect your network. I am not sure that is how they intend it to be read however.

 

[ianmacd]

Bad analogy, as some motorcycles have 3 wheels.

Ok replace motorcycles with motorbicycles.

 

[spinlondon]

Ian I'm sorry, but this is becoming farcicle.

You are stating, that the requirements of a Regulation do not need to be met, if it is ignored.

 

[ianmacd]

I did not say anything of the sort. A closer aproximation would be that a regulation does not apply when it's irrelevent. Would you follow safe zones for a bath in a room without a bath? I think not. This is no different. You started this tangent by erronious claiming it was illegal for a dno to supply tn-c-s when not on pme and used an irelevent regulation as your proof. All I did was prove logically that you are mistaken and have tried to explain why in a few different ways but am supprised that you still can not see the error in your argument.

 

[Voltimax]

Three strikes and you're out, I believe is the american term.

C'mon guys, agree to disagree this argument is going nowhere and the mods have already given two warnings. Why not carry on the argument in the form of PM's if you must continue eh?

 

[steptoe]

Im assuming everyone has missed the point about the cable being concentric.

 

[AAAMUSEMENTS]

Bad analogy, as some motorcycles have 3 wheels.

Wouldn't that be a trike?

:innocent

 

[steptoe]

Wouldn't that be a trike? :innocent

it would, and although often regarded as a motorbike(as the poster said) another often misconceived idea,

a trike and a bike are as different as are pme and TNCS,

so a very good comparison I think.

 

[spinlondon]

I did not say anything of the sort. A closer aproximation would be that a regulation does not apply when it's irrelevent. Would you follow safe zones for a bath in a room without a bath? I think not. This is no different. You started this tangent by erronious claiming it was illegal for a dno to supply tn-c-s when not on pme and used an irelevent regulation as your proof. All I did was prove logically that you are mistaken and have tried to explain why in a few different ways but am supprised that you still can not see the error in your argument.

To suggest that someone would apply Regulations pertaining to a location containing a bath, when there is no such location is spurious.

The Regulation relating to PME, clearly states that it only applies where the neutral and protective functions are combined. If you do not realise that this combining of the neutral and protective functions is refered to as TN-C, then there is little point in continuing this discussion.

 

[ianmacd]

Thankyou for ending this tangent as its clear that I am unable to explain to you that that regulation also only applies when the distribution is PME not if its not PME.

I do not think anyone is suggesting that the distribution in 9(1) relates to TN-C BUT only when its also PME. Also I can not see how you are making the immense leap from a regulation that needs to be both PME and TN-C to TN-C is illegal when not PME.

 

[professional]

Oh my god - not again!Use the supplied earth - it's allowed, for god sake.

And if the doubters want me to prove it this time, I will!

Exactly - use the best earth available!

 

[androiduk2002]

Im not going to get into this to deep as I do not know the rules and regs enough.

That being said I asked a few questions at college on this subject, all 3 lecturers asked told me the same thing ,

If under 5 mtrs from main property then use main incoming earth, if over 5 mtrs local authority build regs require the outside buildings to be supplied a CPC by TTing the installation. This is not a BS7671 thing its some local councils building regs requirements this may vary from area to area.

i then asked one of my lecturers about multipal rods to get a better reading, (he is an EX DNO trained sparks) he said it was ok to use multipal rods in fact he has had to before, he has found the best way to do this is to trianglulate 3 rods.

 

[Voltimax]

i then asked one of my lecturers about multipal rods to get a better reading, (he is an EX DNO trained sparks) he said it was ok to use multipal rods in fact he has had to before, he has found the best way to do this is to trianglulate 3 rods.

Equilateral or isosceles?

 

[spinlondon]

Thankyou for ending this tangent as its clear that I am unable to explain to you that that regulation also only applies when the distribution is PME not if its not PME. I do not think anyone is suggesting that the distribution in 9(1) relates to TN-C BUT only when its also PME. Also I can not see how you are making the immense leap from a regulation that needs to be both PME and TN-C to TN-C is illegal when not PME.

Ian, you seem to be under the mis-aprehension that the requirement to provide PME, only applies where PME is already provided.

Why would someone write a regulation requiring PME, only in instances where PME already exists?

I suggest you do a google search for Protective Multiple Earthing.

Let me know how many hits you get, where it is not mentioned that PME is also known as TN-C-S, or vice versa.

 

[ianmacd]

Ok I think I understand your problem. PME is not a presentation it's a distribution and as such you can not have a PME installation like you can have TN or TT. As many many peoe have said before (so I am supprised you haven't understood it yet), PME is not the same as Tn-c-s. In fact you can have a PME network supplying tn-s or even tt but they are not tn-c-s are they?

 

[ianmacd]

Exactly - use the best earth available!

He is. Tt is your earth. It won't send your bonded metalwork or class I accessories to line voltage when the neutral is broken or you won't loose your earth as it's broken on dno side and they haven't realised.

 

[Sidewinder]

ianmacd,

You can't have a "TN-C-S" system supplying a TT "system".

I believe that there is a significant misunderstanding of the ESQCR going on here.

Please remember ESQCR is LAW.

BS7671 is NOT LAW.

I'll look up the relvant legal references and come back later after cutting the lawns and a few beers.

 

[ianmacd]

ianmacd,You can't have a "TN-C-S" system supplying a TT "system".

OMG NO.

There is a difference between distribution and presentation. TN-C-S is presentation not distribution. PME is distribution NOT presentation.

Until you understand that basic concept you can never understand the rest.

Yes a PME Network can supply both TT and TN-S presentation in addition to TN-C-S presentations.

Your specific example, what would you put on the cert if the head was TN-C-S but the Earth was not being used and a rod was connected to the MET instead?