Discuss DIY TNCS - Advise Needed in the Electrical Forum area at ElectriciansForums.net

Status
Not open for further replies.

SKY

Regular EF Member
Messages
416
Location
Essex
Started a job today running in cables, after the customer cleared out the coats and shoes from the meter cupboard I find this DIY bad boy.

A clamp on the outer containment of the incoming main - I did a quick loop test on the socket with reading of 0.40ohms.
Will do a full ZS and ZE when I go there in a few day.

I guess this must have been a TT system in the past but there is no sign of the rod.

Do I need to inform DNO to sort this out?

IMG00292-20120814-1640.jpg
 
S

Spazz

As you did the Zs on the socket it will be higher, you need to do the Ze on the incoming main to get a good reading, you will prob find it is under 0.35ohms
 
OP
SKY

SKY

Regular EF Member
Messages
416
Location
Essex
As you did the Zs on the socket it will be higher, you need to do the Ze on the incoming main to get a good reading, you will prob find it is under 0.35ohms
Cheers understand that - just did a quick test at sockets to ensure that there was earth just to make me sleep at night.
just worry that a earth connection like this will loosen over time.
 
OP
SKY

SKY

Regular EF Member
Messages
416
Location
Essex
Sorry chaps meant TNS.

The DNO own the cable so what do I do??

Should they come out and solder onto the lead.

My NICEIC guidance book says: 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
 

trev

Regular EF Member
Just one thing to say first Sky , it's a DIY TNS.
It has been common practice, amongst the less informed, to put an earth clamp on either a lead sheath or on armourings of incomers where they find a TT. This is done for a number of reasons, either they think they are making it safer because they get a nice low Ze or they do not understand why a rod system is there and how a TT works.
If it's the first well to a point it's true BUT a standard earth clamp is not the right thingto install. it should either be sweated on or should have a constant force spring, as far as I know The DNO should carry out both of these operations although I stand to be corrected there. This type of clamp should never be installed onto the lead sheath of a cable, proper earth rods intended for purpose should be used.
There's acres of discussion and debate on here re TTs and how to get a good effective one
 

rodney12

Electrician's Arms
Messages
152
Location
Derbyshire
Be interesting to know what the neighbours arrangements are, ie tt or tns, but really you could just inform the dno what you have found and would have thought that they would have to come and sort it or even ask you to rod it if it's meant to be a tt

- - - Updated - - -

:smile5:
 
OP
SKY

SKY

Regular EF Member
Messages
416
Location
Essex
Will let DNO know - who is it for Basildon, Essex? (UK Power Network)??
I can TT but I don't think customer will pay, will have to mention it on my EIC as a departure to 7671 if they don't.
I hate things like this.
 
1

1shortcircuit

Will let DNO know - who is it for Basildon, Essex? (UK Power Network)??
I can TT but I don't think customer will pay, will have to mention it on my EIC as a departure to 7671.
I always look around the property beforehand to see if there are any visual faults that sound alarms. Once this is done I then start testing to see if there are any underlying issues with the installation that couldn't be seen. When testing is complete I commence my work and at the end of that... I test all over again to make sure everything is still good.

Obviously there are some people out there that are so good that they don't need to do any of the above and they're even capable of calculating results in their head for the schedule of test results.

I would have spotted this and informed the DNO. It's their equipment so they can deal with it :D
 

La Poste

Regular EF Member
Messages
992
Location
South east
Just about every TNS system I have seen around my way totaling about ten have all had these clamps on them.

I have yet to find one TNS round here with the correct clamp on the outer sheath of the cable.
 

Cbigfoot

Electrician's Arms
Messages
120
looks to me like there is a 2.5/4mm (or most probably a bit of 7/0.29) cable attached to the service, bare tinned copper sweeping around behind the G/Y cables possibly into the end terminal. In which case it is a TNS service.

This wire beloings to the DNO and is the mian earthing point into the MET. The question is should you upgrade it, assume it is not the correct size and suppleemnt it with earth rods, or ask the DNO to upgrade it which they are not required to do as they are not required to provide an earth?
 

Snapester

Regular EF Member
Messages
357
Location
Birmingham, UK
The DNO used to use clamps such as these not so long ago ive seen them on loads of installs and from mates at the DNO. Infact i did it on an install last week whoops........ oh well at least they have an earth with a decent reading, i would leave as you have a decent reading and the DNO well they wouldn't care as they leave properties without an earth alot of the time........
One rule for one and one for another.......... Its safe
 

Snapester

Regular EF Member
Messages
357
Location
Birmingham, UK
When i said safe, i mean that installations done this way are safe and is/has been a chosen method used by the DNO to earth their installations.
I cannot comment on how unsafe the installation the op is on, but with a Zs reading of 0.30 then its pretty good, i would disconnect both main bonding conductors and test the Ze to establish what real reading on the TNS the op is getting.
 

Guitarist

Regular EF Member
Messages
5,250
Location
Norfolk
Personally, I would be telling the customer to get the DNO to look at this. If they deem it ok, then it's out of your hands. If they change the clamp, then all well and good. If they inform the customer that it needs a rod, then you can quote to do that. Either way, let the DNO decide and sleep soundly.
 

Snapester

Regular EF Member
Messages
357
Location
Birmingham, UK
Im with guitarist on this one, DNO need to sort it but i know what they will say. I went to a job with a brand new cutout installed and when arrived surprise there was no earth installed! Nice one DNO..............
 

sparks1973

Regular EF Member
Messages
1,027
Location
Leeds
As you did the Zs on the socket it will be higher, you need to do the Ze on the incoming main to get a good reading, you will prob find it is under 0.35ohms
well as its a TN-S (sheath earth)....as long as its below 0.8....its ok....wheres 0.35 come from for this?..
 

Snapester

Regular EF Member
Messages
357
Location
Birmingham, UK
I think from the fact that he took a reading at a socket of 0.30 so i think he was saying it should be less at the MET.
Although i would take out the bonding conductors to rule out parallel paths providing good earth!
 

sparks1973

Regular EF Member
Messages
1,027
Location
Leeds
if this were me....i would get a Ze in the normal way (disconnect main earthing from MET)....leave that `earthing clamp` well alone....just check its secure...thats all....you have already proven a low impedance (Zs)....it aint your property....and it aint the customers either....ring the DNO by all means....all they`l say is `you`ll have to rod it`...or words to that effect....
 

Snapester

Regular EF Member
Messages
357
Location
Birmingham, UK
How do you know the DNO didnt leave it like that? I have seen plenty of them like that, which DNO class as safe??
The new cutout was installed on existing installation as old cutout had burnt out, it was TNS but they forgot to put a earth on it and let house without an earth.
 

sparks1973

Regular EF Member
Messages
1,027
Location
Leeds
So it was intended by the DNO for that installation to be a TT

Not properly done though which is my whole point
no it isn`t properly done Trev....but the amount of times i`v seen BS951s being used for this.....
 

sparks1973

Regular EF Member
Messages
1,027
Location
Leeds
Yes Sparks1973 and Snapester, I've seen loads like that too guys, none of which have been done by the DNO though
oh it`l be have a go heros alrite Trev..lol....but the proof of whether its good for continued service will be:
1) the visual.....is it secure
2) the test....whats the Ze
 
G

Guest55

DNO will tell you to rod it mate....
No way would I convert tns to tt just because the dno cant be arsed spending 10mins reconnecting their own earth strap.
Get the homeowner to insist on a repair visit.
 

Marvo

Admin and gender confused
Staff member
Admin
Messages
16,214
Location
South Africa
That clamp looks a bit lightweight to me. I would just put 40Amps through it with the loop impedance tester and see if it's good.
 

sparks1973

Regular EF Member
Messages
1,027
Location
Leeds
That clamp looks a bit lightweight to me. I would just put 40Amps through it with the loop impedance tester and see if it's good.
yeah but for how long?....a high loop test is a very short duration test....wont affect that......
 

trev

Regular EF Member
No way would I convert tns to tt just because the dno cant be arsed spending 10mins reconnecting their own earth strap.
Get the homeowner to insist on a repair visit.
If it's a legitimately done TN-S then I wouldn't change it to a TT either Biff but the legitimacy or otherwise of that TN-S has yet to be confirmed. If it should be a TN-S then I too would be insisting that the DNO come out to maintain the earth that they are legally obliged to
 

Marvo

Admin and gender confused
Staff member
Admin
Messages
16,214
Location
South Africa
yeah but for how long?....a high loop test is a very short duration test....wont affect that......
Yep, it's a pulse test but if it gives similar readings at 40A or more as it does on a low current test then it should be stable under general fault conditions.
 
Status
Not open for further replies.

Permanent unswitched live colour?

  • Brown

    Votes: 99 72.3%
  • Black

    Votes: 38 27.7%

Electrician Talk

Electrical Forum

Welcome to the Electrical Forum at ElectriciansForums.net. The friendliest electrical forum online. General electrical questions and answers can be found in the electrical forum.
Top