Bonding water services

[zap]

Hi Guys,
I was going to use the following as a part of my assessment with niceic next month but I'm at a quandary.

The job was to swap a spurred socket outlet with a FCU and spurr off that to two double sockets, one next to the FCU in the hall and the other in the living room on the other side of the wall to which the first was installed.
I've upgraded the earthing conductor to a 16mm² and the main bonding conductors to 10mm² except for the water services.

I tested from a disconnected main bonding conductor at the MET to the water stop cock valve body and the highest measurement attained was 0.04 ohms. This figure seems too low (6mm² and at least 10m long possibly more) and leads me to believe a parallel earth path exists. Also the conductor has green (not g/y) insulation and is 6mm² (should be 10mm²).

Here's my issue: The kitchen has been fitted impressively. I mean all the pipes etc. were jointed after the units were installed. Perfectly formed, circular holes in the back of the sink cupboard. I've never seen such impressive workmanship.
I know, now, that I shouldn't have installed the extra sockets until the earthing arrangements were upgraded but that's history.
The owner of the property is not happy for me to start destroying his lovely kitchen and I'm reluctant to do so. Can I record a limitation?

I'll be very grateful if any of you can help.

 

[SJD]

What would you expect the resistance to be for 10m of 6mm² single core cable (e.g. from the OSG tables)?

 

[Plonker 3]

Why not bond it at the nearest accessible point and note it on the certificate?

 

[i=p/u]

Would you bond the gas if entres gas box in plastic and then copper to combi???

 

[bigbaddave]

Why not bond it at the nearest accessible point and note it on the certificate?

Why bother if the 6mm is ok? I think the op point is it installing it that is going to be pig of a job

What are the earthing arrangements?

 

[Plonker 3]

Why bother if the 6mm is ok? I think the op point is it installing it that is going to be pig of a job

I agree but as the OP says it is for a assessment, just for the sake of a few meters of cable it would be worth doing especially as he has already renewed the gas bond. Also the assesses can sometime be picky, but the maybe he could use a few regs numbers to back his argument up on why he didn't upgrade it.

 

[bigbaddave]

They can be as picky as the want but if it complies as per the regs then if it not reasonably practical then I wouldn't be doing it. As above though bE prepared to have some evidence for things you have noted on the cert .

However what earthing system is it?

 

[Plonker 3]

Picky?

Sometimes they think they write the bloody regs and amend as they see fit.

 

[bigbaddave]

Aype.. I had that on my first one. gave him the cert for the job and used the printable ones off IET site.. Anyway first think he said was ahh these dont comply... Really, No there not in the correct format.. Anyway page whatever of the regs and guess what the identical form.. That shut him up

 

[zap]

Thanks for all your suggestions. I have several balls in the air at the moment and unable to sit in front of my computer.
It's a tn-s system.
I haven't checked the conductor resistance yet but I will a bit later when I've dropped some of the balls.

 

[zap]

Aype.. I had that on my first one. gave him the cert for the job and used the printable ones off IET site.. Anyway first think he said was ahh these dont comply... Really, No there not in the correct format.. Anyway page whatever of the regs and guess what the identical form.. That shut him up

Interresting! I have not used the niceic forms, I've used the downloadable forms from the iet which I believe are replicas of those in the bgb.

Back in a while...

 

[zap]

What would you expect the resistance to be for 10m of 6mm² single core cable (e.g. from the OSG tables)?

0.03 ohms - took my eye off the ball and manage to double it before!

... that solved that bit of the equation; moving on...

The gas and power are supplied in a garage. The water, according to the owner, is at the other end of the house.
There's a boiler in the garage and all the pipes disappear upwards. The existing water bonding conductor goes into plastic trunking and it too disappears upwards (not in the same place).

If I could replace the existing conductor without damaging anything I would. But if there's a less destructive solution, all the better for all interested parties.

 

[Rampantchilli]

Picky?

Sometimes they think they write the bloody regs and amend as they see fit.

ive had 2 of my jobs assessed by someone who DID write the regs, his name is in the list of contributors

 

[Rampantchilli]

. The water, according to the owner, is at the other end of the house.
There's a boiler in the garage and all the pipes disappear upwards. The existing water bonding conductor goes into plastic trunking and it too disappears upwards (not in the same place).

If I could replace the existing conductor without damaging anything I would. But if there's a less destructive solution, all the better for all interested parties.

why not bond across all of your boiler pipes, including water, make a note on the cert

 

[D Skelton]

If I could replace the existing conductor without damaging anything I would. But if there's a less destructive solution, all the better for all interested parties.

Why haven't you carried out an adiabatic equation? Chances are the csa of the water bond is fine as is.

 

[keniff]

Isn't adiabatic for main earthing conductors and cpc? Didn't think you could use that for bonding?

 

[D Skelton]

Correct, so on a TN-S system to size a bonding conductor the main earthing conductor must be sized correctly. The OP said he just whacked in some 16mm but I would bet he gave this very little thought. The amount of times I've actually put in a 16mm MEC in a domestic situation because of requirement I could probably count on one hand.

Chances are, the original 10mm MEC was absolutely fine. If so, he could leave the 6mm main bond in place.

 

[zap]

Correct, so on a TN-S system to size a bonding conductor the main earthing conductor must be sized correctly. The OP said he just whacked in some 16mm but I would bet he gave this very little thought. The amount of times I've actually put in a 16mm MEC in a domestic situation because of requirement I could probably count on one hand.

Chances are, the original 10mm MEC was absolutely fine. If so, he could leave the 6mm main bond in place.

You're absolutely correct (and you win the bet), I didn't think too much about installing 16mm² for the MEC because I thought I had to! Have I misunderstood something somewhere?
I'm going to read chapter 54 in the bgb again. I've lost count how many times I've read it, and unfortuneatly the misunderstood is sticking.

 

[D Skelton]

In short the MEC is a protective conductor, therefore it can be sized using an adiabatic equation. The bonding conductors can then be sized as not less than half the REQUIRED size of the MEC. TN-S system that is. Ergo sum, if the required size of the MEC is less than 10mm, then your main bonding conductors can be 6mm.

 

[zap]

why not bond across all of your boiler pipes, including water, make a note on the cert

This would be relatively simple to achieve. Thanks for the suggestion. Now back to ch 54 for the meanwhile.