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Opinion On Tns Earth Clamp?


mk1rob

Question

Hi guys,

 

I've just rewired a property that has a TNS earthing arrangement. The main earth is attached to the incoming supply cable with a BS 951 Bonding clamp. I was under the impression that this was unacceptable so rang the distributor who said it was ok. I then rang NAPIT who confirmed it was not ok. However the guy at NAPIT said as long as I get something in writing from the distributor it will be ok. I then rang back the distributor who sent someone out to have a look. He looked at it, wiggled it and said "that's fine as its what they use these days. Its called a Hepworth bond". He has sent me this in writing so I shall put it with the electrical certificate to the customer.

 

Just wondered what your opinion is on all this and am I doing the right thing? Not sure I can twist the distributors arm any more to change it even though I know really its not right.

 

Cheers

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13 answers to this question

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a 951 clamp is not suitable, however there are some clamps that are and look very similar. providing reading is within limits and you have it in writing that it is safe, then dont worry about it.

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It's not right because the 951 clamp is designed for pipe not cable if over tightened it can damage the cable BUT lots of DNO's ran out of proper clamps so they set about finishing their work with 951 clamps...

AFAIK as long as there is no damage and readings are good then don't worry about it.

Make a note on the cert to cover your backside.

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Ok thanks for that! Yeah reading was fine (0.23ohms). I'll make a note on the certificate too as you suggest  :) thanks!


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I thought the Hepworth system was more of a modified buckle clip. Tensioned by a special tool

951s are prone to work loose due to cold flow pressure creep

I have just done a job where there is a 951 on the sheath 20 mm above the sweated earth from the DNO. The cert for the job ( moving sockets to a higher level,up the wall) states that the cable and 951 were fitted since the existing cable was NOT green and yellow!...go figure

I find it strange that we are expected to add comments./observations etc on an EICR relating to items NOT covered in 7671 YET the EICR is a 7671 document

Just confused

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Although its not correct the DNO's around here will 100% deny  they ever fitted them, although i have watched them do it numerous times. I find 50 % of the jobs i visit have them fitted, sometimes in addition to the sweated joint.

Anyhow, why  should we worry its not our equipment and we should not be touching it ; Make a note on your paperwork if you are worried about it. It does sound BS from your distributor as AFAIAA a Hepworth clamp is a  brand of constant pressure spring that looks nothing like a 951 clamp.

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The attitude regarding earth terminals from DNOs across the UK stinks TBH.  None of them seem to have the same criteria.    And typical that the guy thought a 951 was a Hepworth   ( had to look that up )    I only know the coiled constant pressure spring which work a treat ...well....so I'm told ...

 

There are sections of the network in the areas we cover where the earthing has broken down , must be thousands of properties that have high impedance or nothing at all  , but are relying on the gas & water systems for earthing .   And they are rapidly becoming plastic as upgrades are carried out but still nothing is done .

 

DNOs are not bothered because its the responsibility of the homeowner to keep his installation in order........that is only achieved by passing that responsibility on to his electrical contractor , who is obliged to leave the installation in proper order.      Or as we often find ......do the rewire ....fit that shower .....do the bathroom & kitchen refurb .....replace the board ....... and ignore the main earthing situation !!!

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If you are on TNS or TNCS, it is the responsibility of the DNO to maintain integrity of their earthing system. The ESQCR makes this quite clear...

 

24.—(1) A distributor or meter operator shall ensure that each item of his equipment which
is on a consumer’s premises but which is not under the control of the consumer (whether
forming part of the consumer’s installation or not) is—

(a) suitable for its purpose;

(b) installed and, so far as is reasonably practicable, maintained so as to prevent
danger; and

© protected by a suitable fusible cut-out or circuit breaker which is situated as close as
is reasonably practicable to the supply terminals.

(2) Every circuit breaker or cut-out fuse forming part of the fusible cut-out mentioned in
paragraph (1)© shall be enclosed in a locked or sealed container as appropriate.

(3) Where they form part of his equipment which is on a consumer’s premises but which is
not under the control of the consumer, a distributor or meter operator (as appropriate) shall
mark permanently, so as clearly to identify the polarity of each of them, the separate conductors
of low voltage electric lines which are connected to supply terminals and such markings shall
be made at a point which is as close as is practicable to the supply terminals in question.

(4) Unless he can reasonably conclude that it is inappropriate for reasons of safety, a
distributor shall, when providing a new connection at low voltage, make available his supply
neutral conductor or, if appropriate, the protective conductor of his network for connection to
the protective conductor of the consumer’s installation.

 

john...

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Apprentii,  note the last paragraph though ,   "  ..unless he can reasonably conclude  that it is inappropriate for reasons of safety etc etc ..."

 

What happens in the areas I mentioned is they announce that the network cable sheath has broken down ( which it has)   and that PME cannot be supplied on the present system.         

 

Last one we did,  had to fit 6 rods   ,  and the reading is still not really what I'd like to see.     We,re back there shortly so I'll be re- checking the reading . Seriously thinking of  some 22mm copper pipes buried in the garden.

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but that only applies to new connections... for existing, if its been provided then it must be maintained

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but that only applies to new connections... for existing, if its been provided then it must be maintained

 

In my experience they then deny they did ever provide one, even though there's a sweated on cable  going to an old brass stud on the meter board.

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tbh, i never have that problem. rarely ever have an earth issue here, but when it does happen, they are usually pretty good at sorting it

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UKPN don't do much if there is no main earth. If its a cast iron head they will change that and add an earth, least thats how I get round it. :)

 

There are bits of London where its fairly common to have no suppliers earth and no PME in the same area, dunno if the two are linked? 

 

:)

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Yes  Bluey ,  thats the same as in parts of Brum .......the network cast joint boxes have corroded , the clamped earths are lost ,  and because their neutral is'nt rodded  at whatever distances , they refuse PME  and its up to the contractor. 

 

 

And years ago we were told by the original DNO  ( MEB )  Midlands Electricity Board that with the original domestic supplies , they were not obliged to furnish an earth connection .

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