New CU, but bonding not 10mm2. What to do??

[silentboarder69]

Hi,
my first post, so please be gentle. I arrived on site, checked EFC and bonding. EFC OK, but only one 6mm2 bonding present for gas and water. When I ran a lead from the earth bar to the gas I got a reading of 1.04ohm and 1.02ohm for the water.
I upgraded the main earth to 16mm2, but running new bonding isn't favoured by the customer due to inconvenience etc.
Where do I stand? Should I not do the upgrade, or is it OK with it's current bonding?

Thanks in advance!

 

[Mr Mark Sparks]

the reading of the bonding should be below 0.05 ohms and in theory it needs to be upgraded

so what do you do...............

 

[Deleted member 9648]

Is it TNS?....in which case 6mm is ok....if TNCS it should be upgraded to 10mm ,but as long as there is no signs of overheating you can take the decision to leave it and note it as a deviation on the cert......In 30 odd years I have NEVER seen a problem which could be attributed to a 6.0mm bond on a TNCS.......1.04 ohms??....is it a long run of 6.0mm or a dodgy connection? You would expect a lot less.

 

[silentboarder69]

So if you got a reading of 0.05 ohms, but couldn't see any bonding, this would be OK? And if you installed 10mm2 and the reading was 0.09 ohms, this wouldn't?

 

[Deleted member 9648]

Bonding must be visible for inspection.....I dont know anyone who actually records the continuity reading of main bonding they have installed......install and forget.

 

[Mr Mark Sparks]

1. i would note on the cirt main bonding not visible test readings sugest bonding is present,
2. by the book it should be not more than 0.05

i dont make the rules however strange they are.

 

[silentboarder69]

Thanks Mark, I was struggling to find that figure!

 

[Mr Mark Sparks]

Thanks Mark, I was struggling to find that figure!

i havnt got it in front of me its from memory and i have been wrong!!!

 

[WayneL]

Resistance of the bonding should be 'negligible' - that's why they quote 0.05.
That way you are maintaining the 'equipotential'.
If you start running bonding with high readings you will end up with differing potentials between parts.

Bonding must be visible for inspection.....

Are you sure? Or is it just the connections visible for inspections.

Might struggle in some situations to keep the bonding visible along its whole length.

 

[Deleted member 9648]

Bit picky tonight Wayne?

 

[telectrix]

Resistance of the bonding should be 'negligible' - that's why they quote 0.05.
That way you are maintaining the 'equipotential'.
If you start running bonding with high readings you will end up with differing potentials between parts



Are you sure? Or is it just the connections visible for inspections.

Might struggle in some situations to keep the bonding visible along its whole length.

agreed. connections visible for inspection. until we get see through plaster!

 

[Sintra]

With a reading of 1.04 ohms on a 6mm the run would be about 350M are you sure it is properly connected and continuous?

 

[WayneL]

Bit picky tonight Wayne?

For the OP

If my calculations are right, (sad, aren't I), 27 meters of 10mm gets you 0.05 ohms, 16 meters of 6mm gets you 0.05 ohms.
You would, of course, get resistance from the earth clamp as well.

It does state 10mm bonding for TN systems, though, for 16mm or 25mm tails.

Anyone tell me where it actually says you can leave 6mm bonding in place if it 'looks' OK.

I was under the impression that CU swap etc. requires bonding to be up-graded no matter what.

 

[Jimmy Boy]

I thought although maybe not a reg more good practise, if you can't see the whole run of the the main bonding you should disconnect both ends and measure the resistance with a wander lead ? Other wise how do you know if some plum hasn't chopped it ? Be interesting to know that one for definate for my assesment.
ATB S

 

[silentboarder69]

I'm probably wasn't clear in my original question, but I can't see where it's bonded. The gas main is outside and has no bonding. Where is enters the house it's currently not accessible. So I haven't seen any clamp. On the CU there is one 6mm2 cable (other than the main earth). If I run a lead from the CU earth bar to the gas running into the boiler, it reads 1.04 ohms, so some of this will come from the pipes and the clamp before (presumeably) the 6mm2 cable.
It's almost the same with the water, except I can't get to the water main as it is on the cellar. We don't have access to the cellar as I'm working in a flat onthe first and second floor.
I suppose if I gained access to the cellar, found the EB clamp, and got a reading of less than 0.05, this would be OK. With the gas I'm obviously going to have to add EB.
Where the gas enters the flat, it runs under floor boards initially. So if I added the clamp to the first 600mm of pipe in the dwelling, and then put the floor boards down again, this wouldn't meet regs as you wouldn't be able to inspect visually or with a lead at a later date. So I'm thinking the next option is to place the clamp within 600mm of the main, but then I have to run the cable up the outside of the building where it's not protected from the elements. They won't want trunking on the outside of their original Victorian flat.
Thoughts?

 

[malcolmsanford]

What you got to remember that Reg 544.1.2 states shall be made as near as practicable to the point of entry. That 600mm also where as practicable, it then goes on to say that the only certain thing is it must be made before any branchwork. So in theory 600mm is best, in the real world bond in the best position before a branch, so if that is 3 meters then 3 metres it is, just do it before any branch.

Now the bonding to that flat must be done in the flat, so forget the cellar. You will most likely find that it it may be 6mm where you can see it but it may have a joint and a length of 1mm inserted. I personally have seen this a 6mm cable from the gas pipe entry in the kitchen and when it went under the floorboards there was a connector block and a 7metre run of 1mm^ to another connector block and then 6mm again to the MET.

Now the bonding for a TN-S clearly states in reg 544.1.1 that it must be no less than half the CSA of the protective conductor. The protective condutor for the installation is either worked out by reg 543.1.3 or by table 54.7. If you have worked out that your protective conductor can be 10mm^ then you can use a 6mm^ as per reg 544.1.1, but you have to be able to prove this with your calcualtions if ever anything went wrong

 

[Ampere]

Did you null meter before testing using a long lead from main earth to gas and water? sounds like readings obtained included the wander lead.

 

[Jimmy Boy]

The resistance of the lead should be stamped on the wander lead if you can't null it