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please can you explaining this, in my mind say you are 30 meters from the transformer the resistance would increase the further away you are. and putting down a rod will only acheive x amount reading unless you put it in further hitting a more conductive soil or water table.

 
please can you explaining this, in my mind say you are 30 meters from the transformer the resistance would increase the further away you are. and putting down a rod will only acheive x amount reading unless you put it in further hitting a more conductive soil or water table.
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Yes, can you explain this! Cheers

 
An electrode will have a resistance to the mass of earth around it, so increasing is size and length will decrease the resistance, or place them in parallel which is the better option.
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I agree but disagree :|

Tests have shown that deeper driven rods offer a greater percentage of reduced resistance than those in parallel.

However it is often easier to get rods in parallel than deep.

 
if a rod is hit in to a lump of stone then the reading will remain the same until it hits a more conductive material e.g damp soil below rockif the site is based on a slate mine then i would guess there is a serious lack of soil for the reading to be reduced.

how do you come to values for resistance when you do not know how far the site is from the transformer, resistance of the slate ect ect.

i cant see you will get the reading down by much with any length of rod or conductor.

going back to my suggestion that you put a rod down at the mains this will lower the slate ect to .35 based on pme in that area then you only have the short distance of slate between mains rod and the cabin rod. also as said this far from a easy fix case and can see this is not the norm.

please let us know how you get on very interested in learning from this.

andy
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In the end I used 2 1200mm rods in parallel. I couldnt get any deeper than this. I was hitting solid slate.

The rods where connected back to the board using 10mm (unbroken) in plastic conduit.

I backfilled the holes with marconite.

Tested Ze and got 295ohms.

I am aware this is above the 200ohms recomendation, however I think this was as low as practically possible under the circumstances.

30mA RCD fitted allowing a maximum Zs of 1666.

All noted on cert.

 
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! ;)
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go ahead, section 16 comes to mind when exporting TNCS

Agreed, so if I (or anyone else) am talking about TN-C-S on a thread, and refer to it as PME, then the likelihood is that it is PME, so there is no need for Steptoe to continuosly interupt threads with the comment 'TN-C-S IS NOT PME'WE KNOW!! WE GET IT!! :)

.
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so why do we keep getting people assuming it is the same?

if it is PME then it can easily be stated, and not taken to be assumed it is NOT or otherwise,

does anyone state they have a T install? or a TN.?

Nice one, the above comment makes the comment below also a lie;\
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Steptoe, you really are annoying:)Everytime someone mentions 'TN-C-S' and 'PME' in the same sentence you have this same rant.

Now is the time to come clean - let's see how clever you really are;)

One question,

What else can TN-C-S be, then?
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Unfortunately, incorrect. :) CNE (Combined neutral and Earth) is just another name for PME.

Lets wait and see what Steptoe has to say;)
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and you call yourself a spark,?

yet another reason I have decided to take a break for a while

You're close to the answer that I was looking for, but I wanted to hear it from Steptoe - with his reasons for ranting on every time it's mentioned.The system you are looking to describe is actually PNB (Protective Neutral Bonding), although the rod isn't necessarily at the star-point.

Both PME and PNB are forms of CNE, and both can be used to supply TN-C-S.

BUT.......

PNB is used rarely - it's specialist.

You're not going to find it on a housing estate in Birmingham:D

It can, as you say, be implemented by someone with there own supply/transformer.

If it's from a public supply, it will normally only be used to supply one individual consumer - probably for safety with regards to losing the neutral.

So, when one of the lads on here refers to TN-C-S (PME), there's about a 99% chance that they are right, with regard to the system that they are describing, and about a 1 % chance that they are describing a TN-C-S (PNB) system in error.

So is there really any reason to rant on every time someone mentions the two together?? ; \
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PNB is NOT rarely used, just perhaps not used commonly on housing estates,

bit like IT I suppose,

if you havent seen it you ignore it and get your information from a book or WIKI I would suppose in your case.

as I said prev, my motives from posting less are I think pretty much self explanatory for those that know me.

I have also had a difference of opinion this week from a spak that tried to state that you could tell if an installation was 15th or not if it used 16mm tails,

no-where in the regs is that stated, its a stupid localised utilities thing,

Im gonna leave it there and suggest you actually learn the trade before you start trying to quote copy and paste's to people that have been there,

and Im sure many other posters feel similar to me.

 
You've been posting less because you've been caught out more - you're not as clever as you make out to be, and people are realising that.

All you've done in the above reply is re-post everything I've said.

You haven't denied anything I've stated, or offered any kind of counter-argument, yet you criticise my right to call myself a spark.

The only thing you've commented on is that PNB is not rare.

Well I say it's rare - if you compare it's usage (on a public supply) to PME.

As I've said earlier, if you've got TN-C-S on a normal domestic/commercial supply the chances are it's PME - the DNO won't give a street of houses PNB.

So when anyone on here says "I'm doing a CU change, it's a tn-c-s (PME) system - leave them alone, 'cause they're probably right!

 
You've been posting less because you've been caught out more - you're not as clever as you make out to be, and people are realising that.

All you've done in the above reply is re-post everything I've said.

You haven't denied anything I've stated, or offered any kind of counter-argument, yet you criticise my right to call myself a spark.

The only thing you've commented on is that PNB is not rare.

Well I say it's rare - if you compare it's usage (on a public supply) to PME.

As I've said earlier, if you've got TN-C-S on a normal domestic/commercial supply the chances are it's PME - the DNO won't give a street of houses PNB.

So when anyone on here says "I'm doing a CU change, it's a tn-c-s (PME) system - leave them alone, 'cause they're probably right!
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if its PME then simply say so, stating TNCS is dubious, obviously you havent worked in so many places for any period of time to remember when PME was far less common than it is today under TNCS.

since when in the supply regs did it become un-necessary for the DNO to not state PME on the cut out?

when you catch me out (as you call it) then I will happily hold my hands up, Im not here to be twisted, just to offer my few years of experience, but people like yourself make it increasingly frustratingly difficult to do so, and in all honesty I have much better things to do than react to your misinformed (sometimes) statements.

ADS, you dont have to answer this if you do not wish to, but have you actually served your time as a spark? and if so, when?, thanks.

 
ADS, you dont have to answer this if you do not wish to, but have you actually served your time as a spark? and if so, when?, thanks.
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Don't think I've ever referred to myself as a spark on here anyhow, but I served my time from '82 to '86 - that's all you're getting:)

Anyway, back to the important stuff -

go ahead, section 16 comes to mind when exporting TNCS.
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are you telling me in all your 'years of experience', you've never seen the diagram below, showing the two methods of providing power to outbuildings?

And you've never read this leaflet?

http://www.theiet.org/publishing/wiring-regulations/mag/2005/16-elect-inst-outdoors.cfm?type=pdf

Funny that;)

TN-C-S.jpg

 
I served my time from '82 to '86 - that's all you're getting:)
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porridge_468x502.jpg


 
I don't quite understand why this argument carries on.

The law in Gt. Britain (as in many other countries), requires TN-C-S to have PME, and has done so since at least 1988.

As the conversion to PME started in the 70s, it may well be that the law was introduced earlier than 1988.

I do know that in 1982, we were installing PME to new TN-C-S distribution networks, and that we were at that time required to ensure that at no point was the resistance between neutral and earth greater than 20ohms.

Why people keep bringing up the theoretical scenario that TN-C-S could be distributed other than by PME, I don't know.

It is not recognised by BS7671, and is not allowed by the electricty supply regulations such as ESQCR 2002.

 
Don't think I've ever referred to myself as a spark on here anyhow, but I served my time from '82 to '86 - that's all you're getting:)Anyway, back to the important stuff -

are you telling me in all your 'years of experience', you've never seen the diagram below, showing the two methods of providing power to outbuildings?

And you've never read this leaflet?

http://www.theiet.org/publishing/wiring-regulations/mag/2005/16-elect-inst-outdoors.cfm?type=pdf

Funny that;)
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and you are making a statement that they are legally binding documents?

do what you want,

I'll laugh when you go to court and try to use that as a defence for killing some innocent person through your incompetence

typical of the dont care just pay me attitude that is dragging our trade down, while everyone else suffers due to your john wayne attitude.

 
Gentlemen, if you want this thread to stay open keep it nice.

We will not tolerate personal digs or insults.

At times this thread is very close to the line.

 
I don't quite understand why this argument carries on.The law in Gt. Britain (as in many other countries), requires TN-C-S to have PME, and has done so since at least 1988.

As the conversion to PME started in the 70s, it may well be that the law was introduced earlier than 1988.

I do know that in 1982, we were installing PME to new TN-C-S distribution networks, and that we were at that time required to ensure that at no point was the resistance between neutral and earth greater than 20ohms.

Why people keep bringing up the theoretical scenario that TN-C-S could be distributed other than by PME, I don't know.

It is not recognised by BS7671, and is not allowed by the electricty supply regulations such as ESQCR 2002.
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because its not,

its distributed by a concentric cable, and unless you live in an inner city there are lots of instances where its not PME, and if it is then why are my PFC readings so different?

the resistance between N&E on a true PME should be neglible, its the same cable spiked all the way back to star point,

do I need to do a drawing to show how PME differs from TNCS.?

 

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