TT system.

[ADS]

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.

Sorry, have to butt in again.

About as likely as 'rocking horse p**', with a PME distribution.

This is why they supply TN-C-S under PME conditions - to allow for this unlikely event.

This is also why they won't distribute PNB to multiple TN-C-S installations in case of loss of supply neutral.

PNB supplied to solitary consumers only.

It really isn't difficult to understand.

 

[ianmacd]

It doesn't matter how likely but it can happen. Also the loss of an Earth on TN-S is not that uncommon and often remains undetected for some time. Neither will happen if you are in control of your Earth.

 

[ADS]

Then why don't we get rid of the other two and TT everything

Because the other two are efficient means of earthing.

Yes, TN-S earth can deteriorate to unacceptable levels.

This is why Ze is an important measurement on PIRs and during alterations to ensure a good earth path.

But the loss of supply neutral causing a problem?? I'm not convinced.

If PME conditions apply, which we have established that they will on 99% of TN-C-S installs, then I'd like you to tell us where the neutral could be lost as to cause a problem to the degree that you describe.

I spoke to 'Scottish Power' sparkies in a substation a couple of weeks back and they had never heard of it happening.

And if you google it, I doubt you'll find many hits - I didn't.

Once again, unsubstantiated info being given out on forums.

 

[ianmacd]

But the loss of supply neutral causing a problem?? I'm not convinced.

Then you are a loon. The networks described as PME here are not in fact as safe as networks in other countries which are safer as they tend to also put an Earth rod/something at the consumers installation too (on the PEN conductor) so its proper PME.

What would happen if your neutral broke your side of the last earth rod (and its probably not that close)? And don't think an RCD will help as it won't.

 

[ADS]

Then you are a loon.

Nice!

The networks described as PME here are not in fact as safe as networks in other countries which are safer as they tend to also put an Earth rod/something at the consumers installation too (on the PEN conductor) so its proper PME.

What would happen if your neutral broke your side of the last earth rod (and its probably not that close)? And don't think an RCD will help as it won't.

I think you'll find that the supply neutral is rodded 'before' and 'after' - if you get my drift

My house, for example, will be rodded somewhere before it reaches my front door, and then again afterwards, at some point further down the line.

This is the whole point of Protective Multiple Earthing - and as you are unlikely to lose the supply neutral at all, let alone either side of your property, then there isn't much chance of your exposed/extraneous metalwork carrying the whole streets electric, is there.

So like I say, I'm not convinced it's quite the issue you make out.

And another thing - how come you are very selective about which parts of peoples posts you respond to, and which parts you don't.

You, and a few others on here, have this knack of picking out one comment in a post, and then sidetracking away from anything important the poster might have said.

Is this because you don't have an answer

 

[ianmacd]

So YOU have TN-C-S and a rod at your head installed by the DNO? That would be unique for sure.

 

[Zeespark]

To Me (I may be incorrect here), but isnt there an issue of preventative maintenance not happening these days on DNO supply cables? ie no maintenance happening whatsoever? If thats the case, then surely TT would generally be the best way to go in a majority of installs as TT isnt reliant on DNO service cables?

AndyGuinness

 

[Andy™]

maintenance is often only done on failure

 

[ADS]

So YOU have TN-C-S and a rod at your head installed by the DNO? That would be unique for sure.

There you go again - picking the bones out and ignoring the rest.

I didn't say I had a rod installed at my service head.

'Before it reaches my front door' could be 2 streets away - as could the next rod after my property - but still rodded either side.

Add to that the fact that the supply is probably a ring main running through a few sub-stations, I think I'm safe with my TN-C-S(PME)

 

[ADS]

[quote name='Andy

 

[ianmacd]

So if a digger accidentally sliced a neutral connection after the last rod, you think you would survive being the link to earth? What about your neighbour getting out of their cast iron bath?

 

[wozz]

There you go again - picking the bones out and ignoring the rest.I didn't say I had a rod installed at my service head.

'Before it reaches my front door' could be 2 streets away - as could the next rod after my property - but still rodded either side.

Add to that the fact that the supply is probably a ring main running through a few sub-stations, I think I'm safe with my TN-C-S(PME)

ive lost this one a bit, could you explain after your property, are u meaning a looped supply?

 

[Andy™]

So if a digger accidentally sliced a neutral connection after the last rod, you think you would survive being the link to earth? What about your neighbour getting out of their cast iron bath?

lost neutral is much more likely to happen on overhead. high load etc could easily take only the bottom line

 

[ADS]

ive lost this one a bit, could you explain after your property, are u meaning a looped supply?

From what I understand, if PME is correctly implemented, it should be rodded at the end of the run, as well as at various intervals along it.

Don't get me wrong here, I am far from an expert on the supply side of things.

I know no more than anyone else on here, and probably less than quite a few of you, BUT..

I'm just a bit peeved at people still spouting things out like they are part of the regs, without any form of substantiating when challenged.

Anyone with an imagination can come up with scenarios of 'Diggers' etc., but I want fact.

Show me where a neutral was lost and lives lost.

How often does it happen in this country?

How many TN-C-S installs - without PME - are there in this country??

You know, lets have some facts, instead of all the Bu*****t.

 

[Zeespark]

I now have TNCS without PME, converted from TT, but I have a grandparent with TNCS/PME.

AndyGuinness

 

[ianmacd]

Since we have not installed EVERY installation in the UK how can you expect anyone to answer that?

It wouldn't happen in other countries because they implement PME properly. Maybe before you post again, you should search some of the previous threads on here about this.

 

[ADS]

I now have TNCS without PME, converted from TT, but I have a grandparent with TNCS/PME.AndyGuinness

Are you sure, because unless you are the only consumer on that particular supply, or you were running your own supply transformer, this wouldn't be allowed - for the very reason that Ian is talking about.

If you think about a radial supply to a 20 house street, all TN-C-S installs, the DNO aren't just going to put one rod in between the transformer and the end of the supply cable.

It'll be rodded before it gets to the street, and rodded again at the end.

Otherwise, with loss of supply neutral at the start of the street, you'll have the whole streets usage trying to find an alternative way back - not good:O

This is why they do it!

Maybe before you post again, you should search some of the previous threads on there about this.

This, Ian, is my whole point.

There are probably hundreds of threads on here all dealing with the same old urban myths.

If we had facts to back statements up, then maybe these same arguments wouldn't keep cropping up.

I like to learn new things as much as the next person, but I'm not going to just take your word for it without you backing up the statements that you make.

 

[Zeespark]

Every house that our incomer (overhead) is TT, and when converted, but have just checked and it is indeed PME. My apologiesheadbang

AndyGuinness

 

[spinlondon]

One of the problems with some peoples understanding of the term TN-C-S, is that they forget who introduced the term.

The term was introduced by the IEE, now known as the IET. They were kind enough to provide a definition of the term.

Some people don't like that definition, and think it is incorrect.

The way I see it, is if you are going to use the term, you have to put up with the definition.

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

As I've said before, if you think the definition is incorrect, then get in touch with the IET.

Myself, I'm quite happy to continue using the term as defined by BS7671, as used by the DNOs and by just about any one else who matters.

 

[ianmacd]

Myself, I'm quite happy to continue using the term as defined by BS7671, as used by the DNOs and by just about any one else who matters.

And as I have pointed out to you before, 7671 says no such thing you just read it incorrectly.