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Topic Title: TN-S converted to TT?
Topic Summary: Why?
Created On: 06 February 2013 07:20 AM
Status: Post and Reply
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 06 February 2013 07:20 AM
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SherlockOhms

Posts: 322
Joined: 05 April 2011

Chaps,

I spotted the above conversion whilst looking at a job yesterday.

The service head was clearly that of a TN-S supply complete with earth clamp, allbeit a 951 type and yet, the main earth cable was disconnected and terminated outside to an earth rod.

Any clues as to why this may have been done.?
If there is a problem with the supply cable then the DNO should rectify?

Just for a bit of added comedy, on the same job, the electric shower was fed from the light switch in the airing cupboard in 1,5mm. No RCD in the building. A new personal best I think?

The subsequent phone conversation with the landlady began "Are you sitting down?".

S.
 06 February 2013 07:31 AM
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primo

Posts: 439
Joined: 10 January 2008

I've had to make a couple of TN-S supplies TT due to poor readings (in fact no reading on one of them) on the supply cable sheath. When the customers found out about the upheaval of having their front gardens dug up to replace the supply cable they opted for the rod instead. In both cases I left the old TN-S earth connection if only to serve as main bonding to the supply cable.
 06 February 2013 08:49 AM
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Grumpy

Posts: 435
Joined: 09 January 2009

I had one recently where checks before a board change showed 0.7 ohms but had risen to several hundred after board change a week later. Didn't need to TT as nice SSE came out and PME'd it. He suggested lead sheath had split where it joined main supply in the street. As above bonding left to sheath.
 06 February 2013 08:50 AM
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Parsley

Posts: 1024
Joined: 04 November 2004

The DNO only has to maintain the earth if they provided the earth in the first place, as there is a 951 clamp fitted maybe they didn't.

Regards
 06 February 2013 11:20 PM
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peteTLM

Posts: 3169
Joined: 31 March 2005

Originally posted by: Parsley

The DNO only has to maintain the earth if they provided the earth in the first place, as there is a 951 clamp fitted maybe they didn't.



Regards


Haha! Where i live is the old eastern electricity board area and there are literally millions of houses with them fitted by the DNO.

P

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Lack of planning on your part doesn't make it an emergency on mine....

Every man has to know his limitations- Dirty Harry
 06 February 2013 11:51 PM
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ebee

Posts: 5711
Joined: 02 December 2004

Yes next door to my area (The old YEB) are fitted some inferior (Prior BS 951) earth clamps on the lead sheath. Just about one up from a buckle clip. Current carry capacity about the same as a paperclip I suspect.
At least my old area (Norweb) had sweated joints (OK not much bigger than 30A fusewire I admit. LOL

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Regards,
Ebee (M I S P N)

Knotted cables cause Lumpy Lektrik
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