2 x 6 mm as main bonding ?

[grandfortune]

Hi all ,got a tricky install as I cant get back to mains and they are having a bathroom refit , I've got 2 , 6 mm earths runing in to roof space can I double these up and use for a main 10mm bond?
Cheers grand

 

[telectrix]

don't see why not, as long as it is documented.

- - - Updated - - -

don't see why not, as long as it is documented. if it's TN-S or TT, though a single 6mm should suffice.

 

[telectrix]

should be OK as long as it is documented on the cert. if it's TN-S or TT, though, a single 6mm should suffice.

 

[Octopus]

what are the 2 x 6mm doing??

 

[grandfortune]

One to main water and one to airing cupboard cylinder , it's a flat so no gas

 

[telectrix]

so, if you already have a main bond to the water, what's the problem?

 

[grandfortune]

itas TN-C-S so i need to upgrade to 10.0mm

thaks for the replys, will double up the 6.0mm

 

[ackbarthestar]

I read something somewhere that stated if the bonding was 6.0mm2 for a TNC-S system then leave it as is.
however, I can't remember where that info came from but was something that caught my eye as being contrary to the regs.

 

[Octopus]

I read something somewhere that stated if the bonding was 6.0mm2 for a TNC-S system then leave it as is.
however, I can't remember where that info came from but was something that caught my eye as being contrary to the regs.

Was 131.8 in the BRB but not sure what it is now as it got renumbered.

 

[Spoon]

Was 131.8 in the BRB but not sure what it is now as it got renumbered.

131.8 (BRB) is now 132.16 (BGB)

 

[Guffer]

6mm ok on TN-C-S if been installed 'for quite some time' and no signs of any heat damage. Seems to be quite a sweeping statement when the tables do state 10mm. It all boils down really to whether that 6mm can carry the return current if you lose incoming neutral ?. Suppose we shouldn't question any get out clauses just agree, write it down and keep smiling.

 

[alanl]

132.16 means you SHOULD upgrade any existing earthing and bonding if they are not adequate, NOT that the current bonding is adequate.

PME/TN-C-S supplies need a main protective bonding conductor according to 544.1.1, which points to Table 54.8, which says a 10mm sq conductor is the minimum required, with other sizes according to the CSA of the neutral conductor.

Guffer, above, is correct, but you shouldnt just guess at what someone has told you on a forum, read the Regs, and see what your installation requires.

To the OP, yes, 2 x 6mmsq will be OK, if labelled and connected correctly.

 

[Tuttle]

I've seen that as well, in ESC Best Practice Guide 6 "Consumer unit replacement in domestic and similar premises"

http://www.esc.org.uk/fileadmin/user_upload/documents/industry/best_practice/BPG6_09.pdf

Page 5, section 6.1, note 3 says: "A 6 mm2 main protective bonding conductor size could be deemed adequate where the minimum size required by Regulation 544.1.1 of BS 7671 is 10 mm2, if the bonding conductors have been in place for a significant time and show no signs of thermal damage."

 

[alanl]

ESC guides are not the Regs, and can be wrong, which if what you said above is correct, then it is wrong now. It may have been correct when written, but not now in most circumstances.

GN8 goes into detail about this, and says, basically, only when the Designer is comfortable that the current, undersized, protective bonding is adequate for continued use, can it still be used.
It has to be recorded as a departure on any EIC/MWC.

Now, can anyone really say that such an undersized cable would be adequate in extreme fault conditions?
For the cost of 10 metres of new 10mm cable,and a hours work, I wouldnt risk it. I'm sure there are people who would, but it is quite clear that leaving undersized protective bonding conductors is the responsibility of the Designer, who, in most cases (on here) is also the Installer and Tester.

Even if you could give a reason for leaving an undersized PBC, what happens if you are questioned about it by your Assessor, or someone else comes along and does a EICR?
Unless a VERY good reason for its use, you would be squirming a bit trying to justify your decision.

 

[Tuttle]

ESC guides are not the Regs, and can be wrong, which if what you said above is correct, then it is wrong now. It may have been correct when written, but not now in most circumstances.

GN8 goes into detail about this, and says, basically, only when the Designer is comfortable that the current, undersized, protective bonding is adequate for continued use, can it still be used.
It has to be recorded as a departure on any EIC/MWC.

Now, can anyone really say that such an undersized cable would be adequate in extreme fault conditions?
For the cost of 10 metres of new 10mm cable,and a hours work, I wouldnt risk it. I'm sure there are people who would, but it is quite clear that leaving undersized protective bonding conductors is the responsibility of the Designer, who, in most cases (on here) is also the Installer and Tester.

Even if you could give a reason for leaving an undersized PBC, what happens if you are questioned about it by your Assessor, or someone else comes along and does a EICR?
Unless a VERY good reason for its use, you would be squirming a bit trying to justify your decision.

I think this guide was updated last year, so is fairly recent. It does only cover consumer unit replacement though. I don't think that it is saying that it is fine to use 6mm instead of 10mm, I think that it is saying that you don't have to refuse to replace a consumer unit just because the bonding is 6mm where it should be 10mm.

The way I see it is that if you are changing a consumer unit and the existing bonding is 6mm instead of 10mm and can not be replaced, because it goes though a nicely decorated kitchen or something, then you can use this guide as justification. You are after all probably making the installation safer by updating the consumer unit.

Maybe I need to get myself one of those tin hats.