TNS or TNC-S

[initforthemoney]

Different criteria on sizing of Main Bonding Springs to mind....

Not at all.

Main earth 16mm and main bond 10mm on both types.

 

[a1spark]

Is it not true that on a TNS system the Main Bonding can be 6mm ?, whereas on a TNCS system it has to be min. 10 mm.

so : It doesnt really matter if its TNS or TNCS. is not correct.

I see what you are saying i.e err on the safe side [ On-site goide etc] and you cant go wrong but from a design point ,or if considering the outcome of a PIR, then its important to keep in mind the differing minimum requirements between the two systems

 

[initforthemoney]

Is it not true that on a TNS system the Main Bonding can be 6mm ?, whereas on a TNCS system it has to be min. 10 mm.Its the same for both Page 28 OSG

so : It doesnt really matter if its TNS or TNCS. is not correct.

It is.

My black.

 

[a1spark]

Infor. Yes I did mention the on site guide, but that is not the Regs, its a means of compying with the regs without having to do too much design work -calculations etc. If you read back on my post you will see one of the things I refered to was PIRs. So if you did a PIR and there was for example : 60A main fuse : 16mm Tails : 10mm Main Earth 6mm Main Bonding conductors ... would you mark anything down as a deviation from the Regs Or would you have to check whether it was TNS or TNCS first before deciding...have a think then consider what you stated i.e It doesnt really matter if its TNS or TNCS.....what do you reckon ?

 

[ianmacd]

Infor is correct as the only regulations about sizing refer to PME not TN-C-S .

 

[a1spark]

Infor is correct as the only regulations about sizing refer to PME not TN-C-S .

yes , very Good Ian

The Discussion has however, moved on to a point regarding the difference in Installation design considerations between TNCS & TNS systems.. I think you would agree with the points made by me in refernce to this.

If we do go back to the original discussion then,

I do note you said earlier --

PME describes the Distribution Networks PEN arrangments, nothing more. are those arrangements referring to " external; to the installation", internal ,or both ?

 

[ianmacd]

yes , very Good Ian The Discussion has however, moved on to a point regarding the difference in Installation design considerations between TNCS & TNS systems.. I think you would agree with the points made by me in refernce to this.

If we do go back to the original discussion then,

I do note you said earlier --

PME describes the Distribution Networks PEN arrangments, nothing more. are those arrangements referring to " external; to the installation", internal ,or both ?

Indeed PME does describe that and to that end there will be TN-C-S, TN-S and TT installations where PME conditions apply (i.e. are supplied by a PME network even if the installation is not making use of the Earth from a PME'd PEN) so maybe we should always assume PME conditions apply.

 

[a1spark]

Hi, Ian. I support fully the content, if not the terminology of your post above.

Could you give clarification of your comments

Infor is correct as the only regulations about sizing refer to PME not TN-C-S. ---[b.S 7671 2008 ?} and..

PME describes the Distribution Networks PEN arrangments, nothing more

Would this not tend to suggest B.S. 7671 is regulating DNO practices if PME is as you state external to the installation

 

[ianmacd]

Hi, Ian. I support fully the content, if not the terminology of your post above.Could you give clarification of your comments

Infor is correct as the only regulations about sizing refer to PME not TN-C-S. ---[b.S 7671 2008 ?} and..

542.3.1 mentions PME conditions not any specific Earthing arrangments

PME describes the Distribution Networks PEN arrangments, nothing moreWould this not tend to suggest B.S. 7671 is regulating DNO practices if PME is as you state external to the installation

Not at all. DNO do not need to follow 7671. We do IF we want to comply and use it as a defence/best practise. Also was the ESQCR not updated in line with 7671:2008?

 

[a1spark]

Ian, You clarify my thoughts on the Second of my two questions

and on my Second question you refer to another B.S 7671 Regulation which mentions PME Conditions

The whole point of putting the two questions was to demostrate that in order for B.s 7671 to be able to put in place Regulations for PME then they are specifically refering to PME conditions Within the Installation. i.e at the Cut-out. Refering you once again to Defenitions for PME-----THe Supply Neutral conductor is used to connect the Earthing conductor OF AN INSTALLATION, with Earth------- The whole point I have been making throughout.You have agreed B.s 7671 Cannot dictate on procedures on the Network therefore by defenition their Regulations must be refrring only to the PME connection at the cut-out.

Cant say any more than that Ian, you are confident you have the correct view on this as I am equally confident that I have the correct view ! I am sure you will never agree with me on this one , but hey ! do we Have Too ? !........Thanks for the input all the same.

a1 Spark

 

[ianmacd]

I think the difference comes down to the definition of installation. In my mind when we talk of the installation, it is the customers installation (load side of the meter) but I suspect your view will be that anything on the premises is the installation.

Its one of the many grey areas in the BRB.

 

[a1spark]

I think the difference comes down to the definition of installation. In my mind when we talk of the installation, it is the customers installation (load side of the meter) but I suspect your view will be that anything on the premises is the installation. Its one of the many grey areas in the BRB.[/quote]

Good point Ian. and one upon which I do agree

 

[steptoe]

this has been discussed many times before,

PME is a means of distribution,

TNCS is a means of presentation,

sometimes the 2 can be interlinked and entwinned, but they can also be totally different,

you cannot have a PME without it being a TNCS,

but you can have a TNCS presentation without it being PME dist.

 

[ianmacd]

you cannot have a PME without it being a TNCS,.

Think that should read "you cannot have a PME Earth without it being a TNCS".

A network could be PME and still present either No Earth or a TN-S Earth.

 

[steptoe]

Think that should read "you cannot have a PME Earth without it being a TNCS".A network could be PME and still present either No Earth or a TN-S Earth.

so you cannot have a protective multiple earth earth .....

that doesnt make sense to me.

PME = Protective Multiple Earth

why would I need to add the word EARTH onto it.?

 

[ianmacd]

so you cannot have a protective multiple earth earth .....that doesnt make sense to me.

PME = Protective Multiple Earth

why would I need to add the word EARTH onto it.?

`OK Mr Grumpy-pants, try PME Supplied Earth then.

 

[Sidewinder]

OK, guys Try 544, this does give sizing for bonding for where PME conditions apply and where they do not.

Next, since around 1970 almost all DNO distribution has been CNE, thus by ESQCR, PME. ]

However, this does NOT concern US, UNLESS we are given a TN-C-S presentation for our supply head.

We are therefore allowed to "assume" that PME does not apply unless the cut out is labelled such (ESQCR) or we have other means of formal verification.

We can measure, guess or again assume that we do or do not have PME conditions, however, the only definitive answer can come from the DNO.

In my area they don't have any records so they have to inspect to tell you!

ESQCR my asre! :Blushing

:innocent

; \

 

[green-hornet]

I would have to agree with that, I asked one engineer about the earthing arrangement and he just shook his head and said, they have no idea how many earth points they have or do not have, how the hell can they say its PME? I just laughed. If its not labeled

PME its a TN-C-S

 

[Sidewinder]

Ahh,

There in lies the problem GH, they can not legaly distribute TN-C-S (CNE) unless it is also PME, according to ESQCR!

 

[wozz]

lets face it if there is a 'whos DNO knows least' contest i would win.