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Topic Title: How do you assess the supply characteristics?
Topic Summary: When TN-S not TN-S
Created On: 23 March 2013 03:28 PM
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 23 March 2013 03:28 PM
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Avatar for kj scott.
kj scott

Posts: 2144
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So you look at the service, its a lead sheath service cable; the earthing conductor is connected to the lead sheath.
What is the system earthing arrangements?

TN-?????

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 23 March 2013 04:08 PM
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daveparry1

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Why would you not think it's TNS then KJ?

Dave.
 23 March 2013 04:08 PM
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Avatar for Legh.
Legh

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Umm, Lol,
On the surface, I would state that it was a TN-S, but then after measurement I might decide that it needed an Earth rod, or perhaps the sheath is being used as a PEN such as a PILC cable. Who knows what it is until you scratch around a bit


Legh

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 23 March 2013 04:31 PM
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slittle

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Depends ;-)

It could be any one of three with that much information.

I'd ask the DNO to confirm it. (hard hat on and ducking under desk)


Stu
 23 March 2013 04:42 PM
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peteTLM

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Originally posted by: slittle

Depends ;-)



It could be any one of three with that much information.



I'd ask the DNO to confirm it. (hard hat on and ducking under desk)





Stu


How are they supposed to know then?

Legend has it the old eastern/edf records are rotting away on the floor of an office building in ipswich.

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 23 March 2013 05:16 PM
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tattyinengland

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Kind of knowing some of KJs back ground - I'm looking for a trap here......

I'd treat it as TNS if it looks like it is TNS. If tests are OK for TNS then I'd not seek further (To disprove something that might not be there eg: TNCS)

I know it may not actually be TNS, but how can we do otherwise? Dig up the street?

Regards
 23 March 2013 05:45 PM
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John Peckham

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It could be any system of earthing or no earth at all. Strictly speaking only the DNO can tell you but I wish you luck with that one as you might have more luck ringing the Duke of Edinburgh than getting the DNO to for-fill their statutory duty and tell you. In the London area there are more joints with concentric cable sections between PILC cables in the ground than enough so if you talk to some DNO people they will say it is all TN-C-S PME even though you have a piece of PILC poking up above the floor boards.

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 23 March 2013 06:00 PM
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Avatar for slittle.
slittle

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Originally posted by: John Peckham

It could be any system of earthing or no earth at all. Strictly speaking only the DNO can tell you but I wish you luck with that one as you might have more luck ringing the Duke of Edinburgh than getting the DNO to for-fill their statutory duty and tell you. In the London area there are more joints with concentric cable sections between PILC cables in the ground than enough so if you talk to some DNO people they will say it is all TN-C-S PME even though you have a piece of PILC poking up above the floor boards.


I think you've just hit the nail on the head John, Knowing KJS a bit too well I suspect he's got another odd earthing situation. According to our account manager, PME is available everywhere so a PILC with a separate earth coming off the sheath is most likely connected to the neutral in the first joint rather than finding it's own way back to the star point.

Stu
 23 March 2013 06:08 PM
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John Peckham

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Yes I was around his house some time ago and he told me he had an earthing system that looked like one of the options but was in fact the other so he is probably setting us a trap!

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 23 March 2013 06:15 PM
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Legh

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Well KJS, it looks as though your reputation precedes you ....

Is this a single installation supply or does the cable run up the street feeding properties along the way one wonders ?

Legh

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Why do we need Vernier Calipers when we have container ships?

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"Science has overcome time and space. Well, Harvey has overcome not only time and space - but any objections."
 23 March 2013 07:46 PM
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slittle

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I'll have to stop his breakfasts if he's laying traps again


Stu
 23 March 2013 08:48 PM
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Parsley

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I think the network operators class it all as TNCS unless the installation is supplied from from its own transformer.
There's probably not many of their cables left that haven't got a N-E link somewhere. So I guess all bonding conductors should be at least 10mm.

Regards
 23 March 2013 08:52 PM
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jcm256

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Check if there is a p.d. between neutral and earth, the minute differences in resistance of the different materials lead, copper, can result in a p.d. being set up across them.
Or, another very simple way of checking TN-S is by using an analogue meter on the ohms scale measuring between neutral and earth, it will detect mains frequency and the meter's pointer will oscillate to an fro (tremble) indicating you have a loop path to the mains transformer. The above usually indicates a TN-S. A very low ohms reading and none of the above readings could indicate it is a TN-C-S.
Done it been there don't scowl, but other methods and what the original poster is up to would be welcome.
 23 March 2013 10:48 PM
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alancapon

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If the earth is soldered to the sheath of the PILC, it is likely to be either TNS or TNC-S. If the earth is a clip round the cable, it could also be TT. There are many TT services that were delivered using PILC cable, as it was all that was available. TT would normally come off an overhead network. It would also be fairly normal to connect the armouring of the PILC to the System Neutral at the pole end, to give protection to the service cable, but this does not make it TNC-S!

As JP and Stu suggest, only the DNO can tell you the earthing type. The ESQCR regulations state that they have to tell you the earthing type on request, if you have a good reason for needing to know it.

Regards,

Alan.
 23 March 2013 10:49 PM
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Jobbo

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Last week I had the pleasure of spending a day in attendance, supervising a new 140KVA connection, with UKPN and EDF. It wasn't something I was looking forward to, as all my previous dealings with the aforementioned were complete headaches (this supply had to go live, so the site was prepped, for anything, including 30 pieces of silver) . To my surprise, a long time served engineer turned up, who spent the next 6 hours sharing his knowledge. One of the things he spoke about, was that nearly every connection, be it TN-S, TT was derived from a PME network, like others had mentioned above. He also let me into a few secrets, but I'll save them for another time
 24 March 2013 09:34 AM
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Jaymack

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A girl with big boobs, may or may not have had some artificial enhancement; but the definite way to find out .......... after prodding ........... is to ask!; but don't expect an immediate reply, unless you can prove the appearance.

Regards
 24 March 2013 09:41 AM
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dbullard

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Originally posted by: Jaymack

A girl with big boobs, may or may not have had some artificial enhancement; but the definite way to find out .......... after prodding ........... is to ask!; but don't expect an immediate reply, unless you can prove the appearance.



Regards


I think the mods should have a "like" button ..............

D

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 24 March 2013 01:04 PM
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Avatar for slittle.
slittle

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Originally posted by: Jobbo

Last week I had the pleasure of spending a day in attendance, supervising a new 140KVA connection, with UKPN and EDF. It wasn't something I was looking forward to, as all my previous dealings with the aforementioned were complete headaches (this supply had to go live, so the site was prepped, for anything, including 30 pieces of silver) . To my surprise, a long time served engineer turned up, who spent the next 6 hours sharing his knowledge. One of the things he spoke about, was that nearly every connection, be it TN-S, TT was derived from a PME network, like others had mentioned above. He also let me into a few secrets, but I'll save them for another time



If you get the right guys Jobbo it works well. Knowing who to talk to at the relevant DNO's is in my mind as important as keeping a sharp blade in your stripping knife. They tell me they are trying hard to improve things and I do see some signs of it happening in my area.

Although I hear the Scottish Islands may have a slightly different view at the moment.


Stu
 24 March 2013 02:15 PM
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UKPN

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I wonder how many forum members can identify my avatar?

Regards
 24 March 2013 03:20 PM
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dbullard

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Ok I will get the ball rolling ......

At a stab in the dark I would hazard a guess at PLIC with a BS951 clamp incorrectly used to a MET for a TN-S supply

Regards

D

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..... Dont pee in my pocket and tell me its raining ......


www.quest-electrical-sw.co.uk
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