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Topic Title: TN-S earth clamp
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Created On: 02 November 2004 09:43 AM
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 02 November 2004 09:43 AM
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deleted_zimmerman

Posts: 46
Joined: 01 August 2004

Has anyone here managed to sort out the following:

Lead armouring of supply intake fitted with a TENBY type clamp for the termination of the earth conductor.

I understand why this is not recommended but is there an alternative on the market?

It seems that where installations have this method of termination they will have to be converted to a TT system (unless the supplier will solder a lug to the lead)

Thanks

Rob

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Robert (Zimmy)
 02 November 2004 02:13 PM
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deleted_1_khales

Posts: 1271
Joined: 16 January 2002

Quote

Lead armouring of supply intake fitted with a TENBY type clamp for the termination of the earth conductor.

I have this type of arrangement in my home; but the brass clamp, as provided by the REC many years ago, is somewhat simpler than a TENBY.
Quote

I understand why this is not recommended

Can you elaborate, for the uninitiated?
Quote

It seems that where installations have this method of termination they will have to be converted to a TT system (unless the supplier will solder a lug to the lead)

Can you elaborate on the source for this conclusion (i.e. conversion to TT)?

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khales
 02 November 2004 10:59 PM
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deleted_bryyan

Posts: 59
Joined: 11 July 2004

according to the NICEIC they say the following:

under no circumstances should an earthing clamp (complying with BS 951 or any other) be attached to the lead sheath of any any cable. in the case of a supply cable this practice is wrong for two reasons;

. the supply cable is the property of the electricity distributor and

the securing to the lead sheath is likely to damage the conductor insulation of the supply cable and is likely to loosen over time


BS 951 1999 states in note 3 to its scope that such clamps are not intended for connection to the armour or sheath of a cable

then they go on yo say;

such misuse of a clamp is a depature from regulation 512-05-01

one solution open to the installation designer is to make the installation part of a TT system

Edited: 02 November 2004 at 11:07 PM by deleted_bryyan
 03 November 2004 08:52 AM
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deleted_1_khales

Posts: 1271
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That raises the additional question in my mind of whether or not I should question with the REC whether an existing 2-part clamp on the lead sheath, presumably fitted by them many years ago, is still suitable for the purpose. (I note that their cable connection from from that clamp to the earth terminal block also appears to be under-sized by modern standards.)
What does the panel think? Are today's REC's known to retrofit improved connections, or do they wash their hands of it nowadays?

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khales
 03 November 2004 10:33 AM
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deleted_1_khales

Posts: 1271
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Well, I couldn't wait, so I phoned the tech.support. of our REC's own installation contractor. They advised that a soft clamp (mine is a two-part brass clamp) onto the lead sheath is permitted (thinks: maybe it's the design of BS951 clamps that makes them unsuitable?) and that provided the earth-loop impedance test was satisfactory (under 1/2-ohm, say 0.3ohm), then there should be no need to go to a TT system.

BTW: this discussion thread could usefully be moved to the new 'Wiring Regulations' Forum.

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khales
 03 November 2004 07:09 PM
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barneyrubble

Posts: 46
Joined: 03 September 2004

Around my area on a large estate the supplier has been replacing cut outs over the past few years . Below the cut out they have fitted a tenby earth clamp with 16mm earth wire on the lead sheath and taken into the cut out and the earth terminal is then usable on the side.
As all this belongs to them they can do what they like but it seems the art of sweating a tail has gone, or is it too expensive?
One rule for them another for anybody else.
 04 November 2004 09:13 AM
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deleted_1_khales

Posts: 1271
Joined: 16 January 2002

FWIW the Pirelli Cable Joints and Terminations Catalogue: includes an item on p.53 described as: MECHANICAL EARTH BOND KITS FOR LEAD SHEATHED CABLES; but only for conductor sizes >=35mm2.

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khales
 09 November 2004 01:02 PM
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deleted_zimmerman

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Many thanks to all. Most kind.


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Robert (Zimmy)
 11 November 2004 03:06 PM
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deleted_1_khales

Posts: 1271
Joined: 16 January 2002

Quote

One rule for them another for anybody else.


Its just been pointed out to me that the IEE Wiring Regulations and NICEIC advice do not apply to power supply companies, who work to different rules. Therefore, if they wish to deem any sort of clamp, including a BS915 clamp, as suitable for clamping to their lead sheath, then they can!

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khales
 29 November 2004 11:27 PM
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deleted_DGlenister

Posts: 44
Joined: 29 November 2004

I've come across this situation many times in the past (Used to work for E.M.E.)
We used to fit a Special Strap (Can't remember who made them at present, yes I Can....Hepworth Clamps)
Which consisted of a Tinned copper Strap with a simple buckle, with a Braided copper Strap inside. Installed with a Special tool, Which then formed an Earth "lead" to a Link Block for TN-S.
Since those days I've generally requested that the Customer get in touch with their Electricity Supplier to Organise a PME (TNC-S) Earth terminal to be installed. (Usually costs £65)
As it's not always Pracical or Possible to install an Earth Rod for TT purposes.
Plus the majority of Urban areas Supply cables are generally already TNC-S ready anyway, As when a New cut out is Fitted, Moreoften than not the supply is converted to TNC-S in the process, Particularly in cases where Electrical installation Work was in the process of being carried out at the same time.

Edited: 29 November 2004 at 11:36 PM by deleted_DGlenister
 01 December 2004 03:54 PM
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ARDV8

Posts: 19
Joined: 18 July 2002

I have been involved in the development of a bespoke clamp to allow MICC cabling without an earth tail pot to carry an earth fault. This has so been designed that once attached no damage is incurred by the cable. I would imagine this could be adopted for lead.

This clamp is now being successfully used by Nottingham City Council and allowing for MICC sub mains to remain in situ whilst complying to BS 7671. The clamp has also been approved by NICEIC representatives

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MIET, MIEEE
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