TN-S or TNC-S

[ACDC]

Hello folks.
Need a bit of direction on this one. I went on a survey job the other week, and i need some opinions if the photo shows a TN-S or a TNC-S system? I took a measurment of the Ze, which was 0.54ohms, which suggests a TN-S, but looking at the earth block next to the cut out, there is a solid bar which goes into the neutral connection of the cut out, so could it be TNC-S?

Another thing is the way the flying earth lead connects onto the lead sheath of the incoming supply, this cant be normal practice can it? jubilee clipped, and undersized?

Any thoughts welcome

 

[SPARTYKUS]

Looks TNS to me, it originates from the sheath below, as for the connection I've seen worse!

Bit of a weird one though. Where is it (as in geography?)

Best way is to phone up supplier, if you can get through to anyone with an ounce of sense.

 

[malcolmsanford]

Looks like what you have there is a TN-S and some time in it's history a TNC-S head fitted to the installation.

I would imagine inside the head there is no neutral to earth link and for some reason someone as used the earth terminal on the head as a sort of MET. Best way to tell is do a PSSC and PEFC test, if it is a TNC-S then they would be virtually identical, if it;s a TN-S then the PSCC will be higher

 

[ACDC]

Thanks for the replies guys, much appreciated! Iwont bother phoning the DNO (Been there too many times before being passed piller to post) The site is near Newport S Wales.

Thanks for that info Malcolm, its true when they say you learn something new everyday, will remember that.

Am i right in saying the the lead sheath connection should be soldered? (no clamp used)

 

[Engineer54]

Thanks for the replies guys, much appreciated! Iwont bother phoning the DNO (Been there too many times before being passed piller to post) The site is near Newport S Wales.

Thanks for that info Malcolm, its true when they say you learn something new everyday, will remember that.

Am i right in saying the the lead sheath connection should be soldered? (no clamp used)

Originally it was, you can just make out what looks like the original sweated bare tinned copper earth lead. As this is a 3 phase cable i would remove that DIY jubilee clip and replace it with ''constant pressure spring clamp'' using a braid tail to connect to the installations MET.

If after testing TN-S is confirmed then remove those connections from the cut-out N-E point...

 

[Knobhead]

Constant Force Springs : 3M UK & Ireland

There are two springs and enough braid in a kit for two cables.

Or you could use a Hepworth clamp which the DNO uses, but you need a special tool to apply them.
http://www.sicame.co.uk/Section8/8.05-8.06.pdf

 

[netblindpaul]

Going totally against whet E54 has said & I don't care!
Oh and also Tony the same.

DON'T TOUCH the "jubilee clip" on the cable.
WPD may well know it's there and have left it.
If they do it will be recorded in their system.

They have a policy of NOT removing these live as they have had a few cable blow outs when doing this.
Their current policy is to leave them alone unless they need attention.
Then they do an underground live cut external to the premises, remove the clamp, test & inspect the cable, then re-energise.
Having nearly lost a guy to this they now no longer take risks, so neither should you.
Apart from that you are not "allowed" to work on the DNO kit in the UK "officially" it would be a criminal offence.

I don't know why you have problems contacting engineers at WPD they are very helpful and approachable in my experience as well as easy to contact.


WPD have a statute law responsibility to tell you what the supply is, end of story, under ESQCR.
They may have to attend site to do so though.
This should not be a problem.

 

[Engineer54]

Well thank god i don't live/work in the UK anymore, where as a qualified electrician/engineer your frightened to correct a simple cock-up made by an unqualified/incompedent DIY'er!!!

I don't believe for a New York second that the DNO would even THINK about cutting a cable to replace a TN-S clamp, even less actually do it!!! You don't even need to remove the non-compliant jubilee clip, to perform a good TN-S earth connection, just roll the constant force spring clamps above or below the existing JC. Chopping the cable off and using the new braided cord.... It's a bit different, if it meant taking a blow tourch to the cable, to sweat a new TN-S connection, i'd certainly leave that to the DNO!! Not so sure Tony would though. ..lol!!!

Going by what i've seen of DNO work at service cut-out positions, often performed by un-trained meter fitters, i wouldn't think twice about installing a constant force spring clamp, your not even using a tool of any kind to fit it.

All this crap is one of the reasons why UK goods are so expensive on the world market, all this nonsense has become far too expensive to absorb, so now you pay for it, ...in cash and loss of jobs!! I'm all for safety, sensible safety, but OTT is and will always be OTT!!

 

[Knobhead]

NBP slaps Tony’s wrist.

OK the DNO may have a record of it. In which case they know it’s a sub standard installation and as such should be forced to do something about it.


I’ve worked with paper lead cables since the start of my appenticship. Unless you’re totally cag handed they are as robust as any other cable type. There are a lot of myths and legends grown up around them, they don’t explode the moment you sneeze near them.

 

[netblindpaul]

Well TBH I don't care what you E54 or you Tony have to say or think about this.

The LAW in the UK makes it a criminal offence to do any work on the DNO systems and supply cables and for you to even suggest this makes you both a pair of numpties.

When have related this information it has come direct from linesmen, technicians and engineers at WPD, they have had bad experiences with these clamps so they are no longer prepared to put their guys at risk of a cable blow out.
I don't care how much experience you have or have not.
The fact that you are prepared to suggest to an unknown poster that they attempt something illegal that could end their life if things go wrong IMHO makes you both a pair of fools.
You have no idea of the experience of the OP or how he is likely to go about this.

You 2 have flabbergasted me tonight & thought you were competent, you have just proved me completely wrong.
BOTH of you.

 

[Engineer54]

On this Score, i really don't particually care what you have to say either.
You have your head wrapped up in far too many rules and regulations, that you've forgot what being a qualified electrician/engineer actually means.

All this scaremongery about the law, ....how many times have we heard from members here and elsewhere, that when they have rang the DNOs about lack of earth leads, they have turned round and told them to install it themselves!!! If only you knew what the DNO companies themselves get upto, then talk to me about this and that being against the law, on their installations!!

Your correct both Myself and Tony have a great many years of experience in this industry, more than enough to know that a constant force clamp on a lead or any other type of cable is a more than a safe method of taking an earth.

Two things Paul, ...One, ...i am No Bodies Fool, either Professionally or in my private life, so please get that well and truly straight in your mind OK!! Two, .... Who the hell are you to question my own, or Tony's competency?? I very strongly suggest that you just don't go there!!

Nothing more i'm willing to say to you on this matter, if i do i'll get an infraction!!!

 

[Des 56]

There sure is a lot of fear in our trade nowadays :33:

Perhaps the general lack of supervision or experience before embarking on the road of electrics has engendered this greater caution amongst so many in this trade

Live working is listed as forbidden fruit and should be avoided at all costs,so say the "books"

But the "books" could never and would never be able to say differently
Live working though has always been with us,experience of the job hopefully keeps us safe

I will be live working tomorrow,illegally as well,because that was what electricians were expected to do, and blind eyes turned where necessary
Experience of terminating lead sheathed cable also gives you a feel for its robustness and I would expect a competent electrician to safely clamp a sheath without exploding it

Perhaps inexperience is by far the greater danger to an electrician.maybe not so the danger of "what" an electrician is working with


Now this is a personal view not a war of words with anyone​

, feel free to have your own view and leave me to mine

 

[Knobhead]

Well that’s told me then, I’m officially a numpty! (As defined by NetBlindPaul.)

Paul, take off the rose tinted glasses and look at the real world!

The dangers of cutting and then rejoining a live cable are one thousand times the risk of removing a clamp, but that’s OK in your book of regulations is it?

What is your real world by the way? You can quote regulations verbatim but do you do any real work? For Christ’s sake don’t tell me you work for the HSE!

 

[ACDC]

Cor blimey lads, put the boxing gloves away, it is christmas!
As stated in my original post, i was undertaking a electrical survey. From this survey i will write a electrical report. I have enough experiance under my belt (15yrs) to know what i should or should not touch. Be assured that i will not be touching the earthing connection on the incoming cable, and i will be contacting the DNO.

Thanks again for you replies chaps.

 

[Chr!s]

It looks like an old TNS and now its been converted to a TNC-S and they have just left the clamp on, contact the DNO, most of the UK DNO'S only have TNC-S now and its not a TT .

Regards Chris

 

[Engineer54]

It looks like an old TNS and now its been converted to a TNC-S and they have just left the clamp on, contact the DNO, most of the UK DNO'S only have TNC-S now and its not a TT .

Regards Chris

If it is a PME connection, then there a big problem with it, having a Ze of 0.54 ohm !! lol!!!
No, this is in all likelihood a non DNO connection, made by either an incompetent electrician or trainee or DIY'er who's knows no different!!

No idea about where you live Chris, but i'm reliably told in the Essex area the DNO are still providing TN-S to new builds in areas where TN-S is still the local network system. But i agree with you, most of the much older DNO TN-S networks are now being converted to TNC-S(PME) especially where sheaths are known to be breaking down with age.

 

[netblindpaul]

Tony, E54,
I can't believe that you are still trying to justify your advice.

YOU both, may, well be competent to remove the clamp.

YOU BOTH missed my point.

On a public internet forum, you advised the OP to break the law, and to undertake works that could have injured or killed him.
You had no idea of his background or training, the only information you had was the post and a small poor quality picture.
You both know the state of the industry in the UK, yet you both advised a person of unknown competence to undertake a task, which in the area of the job, the local DNO will not do as they have classed it more dangerous than a live cable cut.

That is my point and I still stand that by it, that your advice was incompetent.

How would you have felt if the next post on the OP's account had been from his widow explaining how he had followed your advice and the cable had blown and caused him to react and be electrocuted, and that his family had now lost their bread winner, she had lost her husband, and his children were now without a father.

You did not know enough about the OP, the situation, the condition of the cable, or the site, or in fact anything to make such a rash and possibly dangerous suggestion.

You both have probably done this on industrial sites in the past, where there is a lot of support and others around.
You may have done this when you were the only person around for miles.

In the WPD area there are a lot of 951 clamps and jubilee clip type connections having been made to their network over the years.
I have not had any of their people admit as to who made these connections, however, when you look at the numbers, then it was certainly not the odd spark or DIY'er.

They have had incidents and reportable accidents when removing these clamps, thus they no longer do it unless they have to.
The cumulative experience of WPD is that to remove one is more dangerous than to leave it, and is also more dangerous than to undertake a controlled, clean, live cut, on an undamaged cable.

So then it appears that between you you are more competent than all of the engineers, technicians and linesmen working for WPD, good on you.

I still think and will continue to think that you were and still are well out of order advising a completely unknown person to tamper with the national grid and undertake a task which is known by the DNO in the area he is doing it as life threatening.

As far as the work I do, yes I do have a lot of work, some of it has to be done live, I work for private domestic clients, for public sector bodies, such as the local authority, schools, and health boards, local & national companies, from sole traders, through SME's to large multinational blue chip organisations, quangos & HM Gov't departments.

One of the reasons I am not on here so much is that I am very busy at the moment.

I not only undertake the actual physical works, but I also undertake the design and the consultancy.

Oh and no Tony as the last paragraph suggests I don't actually work for the HSE, however, I do know a few of their inspectors including the local electrical and controls systems specialists.

I know the legislation and regulations because it is my job to know it.

 

[Engineer54]

I have no idea what your trying to prove here, or who you are trying to impress, but by assuming and/or putting words into my mouth isn't going to get you very far with me!!

I've been around in this industry far too long to be told, that a controlled clean cut of a live cable is less dangerous than removing a jubilee clip. They only time that would come close to being the case, is if that jubilee clip had been tightened to the point, that it had buried itself deep into the lead sheath, and that is clearly not the case here. ....And yes i am competent enough to assess that fact, from the photo provided by the OP!!

By the way, that WPD of yours must have some real cowboy's in their employ, if what you say is correct about all these jubilee clips and 951 clamps they have been installing. From what i can make of your post, it was these WPD employee's buckshee earth connections that they declared too dangerous to remove, ...in the first place!!

You seem to like glossing things up beyond any real recognition, were not talking about the National Grid here, were talking about a local network cable. The difference between them is massive, which is the same as you are trying to make out here. Wrapping a constant force spring clamp around a sound cable sheath is not going to blow up anything, nor is it dangerous by anyone's stretch of imagination, No-ones making any live connections to anything, no-one needs to break any seals, and your not even using any tools for god's sake!!! As regards to the OP's competency, maybe i should have enquired a little deeper, but hey, widows and things, you certainly have some imagination there!!! Geezus!!

The fact that it's against the rules, is neither here or there, and you have made the point which is also fair enough. So what is that different from you breaking the rules when it suits you, and anyone else??

You have turned this into one massive fiasco, coming out with wild and inaccurate statements, along with frankly insulting accusations about my own and Tony's competency. when there was really no need or reason to do so. It just suited your ego at the time to do so!! I really don't need you to tell me if i'm competent or not. Apart from knowing myself, i'll leave that to my present and past employers, who to date, have seemed to be more than satisfied in this regard!!

You can continue to think whatever you like of me, if you think it that will concern me, your going to be sadly mistaken. So long as just think it, and don't voice it, that's fine by me!!

 

[Knobhead]

Paul at the moment I’m still seething.
You call both E54’s and my skill and competence in to question. Based on what? Can you provide any documentary evidence of the danger of removing an earth clamp, you seem to base everything on what’s in black and white, but then resort to “conversations” with your friends. Down the years I trained with a Regional Electricity Board (as they were then) to do live jointing. It wasn’t that I needed it, but the company I worked for thought it would be beneficial for me to gain the experience and knowledge of what can be done. I know what I consider safest, removing a clamp is a small risk. If you look at the construction of a cable you will find that due to the layered nature of a paper lead with it’s infill of oil/wax it is far more resilient than a modern cable.

I took the photo of the clamp in to Photoshop so I could have a very close look at it. I did this before I said anything because as you know my eyesight isn’t what it could be. There is no indentation of the lead. Fitting a constant pressure spring and braid requires no tools and forms it’s self to the contour of the sheath. The DNO’s use Hepworth clamps which require the use of a tool that if it slips could puncture a lead sheath.

At the moment I think an apology to E54 and myself is in order.


But on a personal note I think this is getting totally out of hand!

 

[Chr!s]

If it is a PME connection, then there a big problem with it, having a Ze of 0.54 ohm !! lol!!!

Well, Eon state in there Earthing manual for TNC-S upto 0.8 not 0.35, obviously you wouldn't get a 100 amp without an RCD. lol

No, this is in all likelihood a non DNO connection, made by either an incompetent electrician or trainee or DIY'er who's knows no different!!

Possibly, though if it is a tns a test of the two loops should give an indication.

No idea about where you live Chris, but i'm reliably told in the Essex area the DNO are still providing TN-S to new builds in areas where TN-S is still the local network system. But i agree with you, most of the much older DNO TN-S networks are now being converted to TNC-S(PME) especially where sheaths are known to be breaking down with
age.

Eon are totally free of TNS now, well so they have informed me lol, if it aint TNC-S it TT lol

Regards Chris

 

[Engineer54]

Well, Eon state in there Earthing manual for TNC-S upto 0.8 not 0.35, obviously you wouldn't get a 100 amp without an RCD. lol

Tha's strange, i've not heard of that before. PME has always, as far as i know had a maximum Ze of 0.35 ohm. I'm just wondering if they have started PME'ing all there old TN-S local networks and haven't finished any, thus still relying on the lead sheath of the TN-S cables as the max level!! Who knows, with these new DNO's!! lol!!


Possibly, though if it is a tns a test of the two loops should give an indication.

Agree, it's about the only way your going to get a good indication of what system is actually being provided here...


Eon are totally free of TNS now, well so they have informed me lol, if it aint TNC-S it TT lol

Are Eon only in your area, or do they cover other old regional boards around the country??

 

[Chr!s]

Well there is no defined limit with ESQCR, so Eon work to three limits dependent upon Fuse size. Where they have in-fill developments and service alterations higher value can be expected and you need to design accordingly.

They pretty much cover the midlands and down into bath and Hereford i think.

Regards Chris

 

[nickblake]

doesnt sound right to me set a standard and stick to it , No TNS Eon are always round here and i would say 50% of supplies are TNS

 

[Engineer54]

doesnt sound right to me set a standard and stick to it , No TNS Eon are always round here and i would say 50% of supplies are TNS

Thing is Nick, that doesn't necessarily mean that the local network hasn't been PME'd. It can still appear at the service cut out as a TN-S supply. You will still apply TN-S requirements, whether you know or don't know the DNO side has been PME'd... In other words you go by what you see at the service cut-out!! lol!!

 

[La Poste]

Constant Force Springs : 3M UK & Ireland

There are two springs and enough braid in a kit for two cables.

Or you could use a Hepworth clamp which the DNO uses, but you need a special tool to apply them.
http://www.sicame.co.uk/Section8/8.05-8.06.pdf

Hi there.

Those constant force springs.

Are they like a wrap around arrangement, you know like you uncoil them and then recoil them around the lead sheath?

I have been looking at some pictures of installation and the pictures are not very clear.

I am not about to do this I am asking out of curiosity.

There are loads of TN-S cables around this area fitted with bonding clamps.