Bond a lead sheath?

[AcombAndy]

Went to look at my neighbours CU to do a quick visual as I have been asked to put up a new light fitting. My house is TNC-S (lead sheath) but they have an earth rod by the back door which I wondered about since moving here. I thought they may have been converted to PME, but the installation looks like a TT (16thEd). The earthing conductor comes from the earth electrode to the CU MET and water and gas are bonded from there. What is not bonded is the lead sheath of the incoming underground electricity cable. My first thought was it should be bonded, then I wondered if it would it be better to insulate it, to prevent a downstream fault running a current through the bond to the house earthing conductor. What would be the best course of action - leave it, bond it, isolate it?

 

[NozSpark]

Oooohhhh,

I was going to go off on one then about not creating your own earth by clamping the sheath, but I see that you are considering that the sheath is an extraneous conductive part and should therefore be bonded.

Personally I'd not bond it, I'd phone up your DNO and ask them for somewhare for you to terminate your earth as they have provided an earth, but nowhere for you to connect to

 

[SLIPSHOD & SLAPDASH]

The incoming cable is not your property and you should not tamper or alter it in any way. In saying that i would be tempted to try a Ze test on it.

 

[steptoe]

but dont even think about putting as 951 on it,

bad day explode

 

[SLIPSHOD & SLAPDASH]

but dont even think about putting as 951 on it, bad day explode

Like EDF & London Electricity Board did for the last 50 years without a problem

 

[Manator]

but dont even think about putting as 951 on it, bad day explode

It would hurt the lead.

 

[NozSpark]

Like EDF & London Electricity Board did for the last 50 years without a problem

Plenty around here too,,, but they deny all responsibility if questioned....

"Can't have been us guv, we don't use 951 clamps"

 

[steptoe]

it only takes the one though, :|

 

[Manator]

I have seen this done in various parts of the UK, and each authority deny doing it !!

 

[Evans Electric]

Acom-bandy , you usually find that the Ze on the lead sheath is high or non existant ,so someone changed it to TT . Leave it alone . Check your own Ze ! When you say yours is a TNC-S , is the sheath bonded to the neutral and the earth term within the cut-out? Or is it TN-S?

 

[SLIPSHOD & SLAPDASH]

it only takes the one though, :|

And with 50 + years of this practice being carried out by the authorities please show me any evidence of problems that have arisen, then i may change my mind.

 

[steptoe]

Im not saying by the DNO's

and I havent actually witnessed it myself,

but I have heard of blown cables by heavy handed sparks, and from good sources, not the usual urban spin doctors.

 

[SLIPSHOD & SLAPDASH]

I think i posted this before somewhere here a short while ago. I was watching a jointer moving an old lead sheathed cable for us after he had done a new connection next door. I was amazed how he was roughly treating the live cable and mentioned it. He replied he would rather work on them all day long as the oiled paper insulation is so much denser than pvc he felt safer with it. He tried pushing a screwdriver into a core to show me and it didn't even mark it, let alone go through. I have also played with an old off cut, bent it back & forwards and even hammered it flat, when stripped back have found the cores to be in perfect condition.

I dont believe any stories of service cables going bang because of the 951 clamp. They may have had 951 clamps on & gone bang for a different reason such as a builder moving the entire head, board & meter under a stairs to get a toilet in and pulling it just a bit too much.

 

[steptoe]

I could go with that Slips,

Im pretty much of the opinion its a combination of factors,

movement and a new compression.

and I forgot to take a pic of todays job,

so much woodworm the cutout had parted company from the backboard and was just hanging, being supported by the tails to the meter, old lead sheath TNS

 

[Evans Electric]

SlipperySid reminds me of a posh house refurb 2 years ago .

Builder asks us to move the incoming feed so he could demolish the garage wall , we said no , thinking it would fracture and blow in our faces . Old STA Lead sheathed served cable from around 1920s . Get Central Networks in we said.

No didn't want to pay their fees so they must have moved the thing themselves 6 /7 times in all , and not knowing the dangers it didn't worry them , just dragging it from one side of the drive to the other with us issuing drastic warnings .

Moved it with cut-out and meter still on timber back board and ended up refixing it in a purpose built meter cupboard after driving over it , walking all over it , dragged onto the lawn for a day and left in the rain for a week.

Ignorance is bliss :C

 

[SLIPSHOD & SLAPDASH]

These pics taken about 3 months ago. When i stripped out the house the head was under a stairs, as you can see the stairs was removed and the builder left the meter board hanging from the 1st floor landing by two pieces of 3c 1.0mm. First thing i did was nail the extra wooden supports in. builder says ' what you worrying about, its fallen down quite a few times'

 

[AcombAndy]

Acom-bandy , you usually find that the Ze on the lead sheath is high or non existant ,so someone changed it to TT . Leave it alone . Check your own Ze ! When you say yours is a TNC-S , is the sheath bonded to the neutral and the earth term within the cut-out? Or is it TN-S?

Hi Deke, My Ze was 0.13 last time I checked in June. It is a clamp on the lead sheath to the DNO MET.

Regarding next door the the whole TT installation looks complete and correct. The incomer, meter and CU are in a walk-in cupboard in the middle of the house, so the lead sheath comes right in to the equipotential zone and is therefore simultaneously accessible with the house equipotential zone.. Hence my interest in it ....

I recall checking the Zs to their garage supply back in the summer and recall being relieved it no more than a couple of ohms - I did this as there where 'rotting' extension leads running round the garage which I was able to confirm needed to be put in the bin.

 

[batty]

Builders eh i have worked for quite a few and on one job the meter and board got moved three times by me and that was the old lead cable. I was very careful though. With a bit of organisation it probably would not have needed to be moved at all.

 

[Evans Electric]

Hi Deke, My Ze was 0.13 last time I checked in June. It is a clamp on the lead sheath to the DNO MET. Regarding next door the the whole TT installation looks complete and correct. The incomer, meter and CU are in a walk-in cupboard in the middle of the house, so the lead sheath comes right in to the equipotential zone and is therefore simultaneously accessible with the house equipotential zone.. Hence my interest in it ....

I recall checking the Zs to their garage supply back in the summer and recall being relieved it no more than a couple of ohms - I did this as there where 'rotting' extension leads running round the garage which I was able to confirm needed to be put in the bin.

Is that not a TN-S then Abercrombie ?

 

[steptoe]

Is that not a TN-S then Abercrombie ?

Im confused too Deke

:C