One of my merry men found a house wired as TN-C earthing system, yes it was TN-C not a typing error. He has given me a sample of the PVC/PVC cable from the house. It is a 2 core 1.5mm with red and green cores and marked" Enfield Standard 600/1000 CMA Registered Johnson S Philips". I have not seen that before and yes it was a house in the UK East London in fact.

Anyone else seen this type of domestic installation in the UK?

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John Peckham

http://www.astutetechnicalservices.co.uk/

There were a number of M&S stores wired like that John - there used to be samples of that (type) of cable in the Delta Enfield factory (at least up until the mid eighties). Which reminds me - I've got some 35mm (approx) rubber insulated and sheathed Twin for your museum)

It has been used in quite a number of commercial installations - probably wired by someone doing a "darker" and getting the gear and the thinking from work

It's a bit like old Neozed Distribution boards - typicaly Eire in origin but you'll find loads of them in areas where there was easy ferry access into UK

Regards

OMS

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Failure is always an option

My house had 2-core red + green - i.e. like 6241Y but with the c.p.c. insulated - but it was used in the conventional 'spider wiring' manner (i.e. together with a sheathed single-core black (and some black+c.p.c.) for N).

Sounds to me like someone's been confused by the slightly unusual cable type.

- Andy.

There was up until a few years ago now a department store in Paignton called Rossiter's which had its own transformer and was wired TN-C with the same cable, after it closed the DNO removed the Tx and brought in a supply from the road, the other one I physically know about some years ago that was TN-C was M&S in Bournemouth which I suspect has now been changed.

regards

-------------------------
"Take nothing but a picture,
leave nothing but footprints!"
-------------------------
"Oh! The drama of it all."
-------------------------
"You can throw all the philosophy you like at the problem, but at the end of the day it's just basic electrical theory!"
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Edited: 19 December 2012 at 06:58 PM by rocknroll

wasn't that one wired in single core MICC - live core and a sheath N/E

It used to be a right pain when someone opened a socket outlet and found one live core and a flylead that went to both N and E - and than panicked big style

regards

OMS

-------------------------
Failure is always an option

-------------------------
"Take nothing but a picture,
leave nothing but footprints!"
-------------------------
"Oh! The drama of it all."
-------------------------
"You can throw all the philosophy you like at the problem, but at the end of the day it's just basic electrical theory!"
-------------------------

I know of a farm where the grain dryer is connected TN-C. I've queried it several times and been shown the letter from the then electricity board stating that it had to be done that way otherwise they wouldn't connect it.

On the basis it's been there 30 years, I'm not touching it until the day it needs replacement and then we can start again.


Stu

I wonder what the real risks are other than the rise in the potential difference between exposed conductive parts and the general mass of earth depending on load and cable length?

-------------------------
John Peckham

http://www.astutetechnicalservices.co.uk/

Having spent 3 hours tonight on a turkey breakdown, I've settled with a nice bottle of red so can't be too worried about department stores or grain dryers John

My mate used to work in a lot of the old paper mills.
Just 2 poles.
Phase and return.
Return via the metalwork which sparked at all the joints especially when wet which was most of the time.
Over the years he did get them changed piecemeal to a proper system.

Must admit I`ve never seen an intentional TNC installation myself (plenty of unintentional ones though!)

-------------------------
Regards,
Ebee (M I S P N)

Knotted cables cause Lumpy Lektrik

And the risks of an open PEN?
- Andy.

Fire risks would be the predominant one i suspect john (in addition to the very obvious shock risk by a break in any of the PEN conductors and potentially significantly elevated metal work voltages.

Perhaps the other one is no RCD's ?

regards

OMS

-------------------------
Failure is always an option

I had not thought about RCDs.

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John Peckham

http://www.astutetechnicalservices.co.uk/

well they won't be the most effective of things for ADS and additional protection, that's for sure - although they could provide effective protection from a broken PEN with a suitable electrode and resistor - if BS 7671 allowed us to do that of course

Regards

OMS

-------------------------
Failure is always an option

Of course I see lots of accidental TN-C systems with neutral earth dead shorts that have been on the installations since new. Unfortunately these are not revealed by the 240V bang test although the inspector writes down >200 in all the boxes.

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John Peckham

http://www.astutetechnicalservices.co.uk/

There is a large tower block on the military site in Aldershot that was TN-C from the clients transformer onwards. Some of the floors have been converted with a new DB at the riser and then rewired with separate neutral and earth but most floors are wired in single core MI. Appart from the fact that is not compliant to todays standard we couldn't fail it as it still complied with the standards in place at the time of installation.

Delbot

"Apart from the fact that is not compliant to today's standard we couldn't fail it as it still complied with the standards in place at the time of installation."


So when did you I&T it then 1943? I may have to dig back in to my older copies of the regs.

-------------------------
John Peckham

http://www.astutetechnicalservices.co.uk/

What would you fail it on John - it's a private supply (ie not delivered under ESQCR - at least not at that level)

You probably don't need RCD's, it's wired in MICC anyway, it'll probably achieve ADS.

reg 411.4.3 allow the use of a PEN

this is crown estate anyway so 543.4.2 (i) will probably be in place as will (ii)

So, aside from the usual dross - examining Aldershot under BS 7671 2008 and AMD1 2011 wouldn't raise non compliance for the TN-C aspect alone.

I hesitated to mention it earlier but a proportion of Mod estate has TN-C present

regards

OMS

Regards

-------------------------
Failure is always an option

Before I respond to get shot at OMS. Would you give it an overall "Satisfactory"?

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John Peckham

http://www.astutetechnicalservices.co.uk/

On this issue alone John, I probably would. I would also however present an accompanying report that pointed out associated risk with the installation - technical, commercial, lifecycle, disaster recovery etc.

regards

OMS

-------------------------
Failure is always an option