consumer unit change with undersized main bonding.

[payney 0]

i have been asked to replace a consumer unit and have seen that the main bonding to water and gas are only wired in 6mm. does this have to be upgraded to 10mm so that it meets current regs as its a tncs system. thanks.

 

[Naz]

hi

think the OSG states 10mm, for main bonding to gas and water.

Naz

 

[Octopus]

Time to get out your big green book! BS 7671 131.8 is worth reading and understanding in such situations.

A call to your scheme technical helpline would also be a sensible step (after you've reviewed 131.8).

Hope this helps

 

[Guest123]

It's 132.16 now.:stooge_moe:

Guidance suggests that if the existing 6 mm bonding connects all the extraneous-conductive-parts to the main earthing terminal, has been in place for a significant time and shows no signs of thermal damage, then it may not be required to upgrade it.

 

[ackbarthestar]

Time to get out your big green book! BS 7671 131.8 is worth reading and understanding in such situations.

A call to your scheme technical helpline would also be a sensible step (after you've reviewed 131.8).

Hope this helps

I do love a number chase - lol

Just to add, 543.1.3, then 543.1.4, then onto 544.1.1 but don't forget to check 531.1 which will lead you to 411

 

[ezzzekiel]

It's 132.16 now.:stooge_moe:

Guidance suggests that if the existing 6 mm bonding connects all the extraneous-conductive-parts to the main earthing terminal, has been in place for a significant time and shows no signs of thermal damage, then it may not be required to upgrade it.

have to use this on lot of properties lately as company dont want existing bonding altered which i wasnt happy about so i now quote above on test sheet for qs to sign (providing bonding checks out of course)

 

[Octopus]

It's 132.16 now.:stooge_moe:

Guidance suggests that if the existing 6 mm bonding connects all the extraneous-conductive-parts to the main earthing terminal, has been in place for a significant time and shows no signs of thermal damage, then it may not be required to upgrade it.

Dam, its Jan 21st and I haven't got this far in the new green book.

 

[SPARTYKUS]

Dam, its Jan 21st and I haven't got this far in the new green book.

Youre well ahead of me still....no green book even

 

[ezzzekiel]

is that regulation a direct quote from new bgb lenny? (dont own one yet, single copy held in boss office for reference)

 

[Octopus]

Youre well ahead of me still....no green book even

Sole trader, my Elecsa review in early September raised the fact I must have it before the end of the year!!

 

[telectrix]

what green book? :icon6:

 

[Guest123]

is that regulation a direct quote from new bgb lenny? (dont own one yet, single copy held in boss office for reference)

No, not exactly.

In BS7671, 2008, 131.8 basically stated that no addition or alteration should be carried out unless the earthing & bonding requirements were adequate.

In BS7671, 2011, 131.8 has now become 132.16 and is worded slightly differently.

The guidance I referred to was from the ESC guide on CU upgrades were a TN-C-S earthing system is present.


This is the actual text......


"The minimum main bonding conductor sizes specified in Table 54.8 were first introduced into the Electricity Supply Regulations on 1 October 1988. Smaller minimum sizes were accepted by some electricity distributors prior to that date, but the sizes given in Table 54.8 were introduced to reduce the likelihood of main bonding conductors overheating due to the PME network circulating currents which the conductors may have to carry continuously or for long periods. Distributors may specify larger main bonding conductor sizes where local network conditions require this.

Where a designer finds, in an existing installation where PME conditions apply, that the main bonding conductors have a csa of say 6 mm2 rather than 10 mm2, the designer may, having carefully considered all the circumstances, conclude that the deficiency does not pose a significant risk to the users.
For example, if there is no evidence of overheating of existing main bonding conductors and terminations, it may be reasonable to assume that the existing arrangements are adequate for any network circulating current (unless the main bonding conductors were only recently installed). However, the deficiency must be recorded, together with the reasons why the installer has concluded that the deficiency does not pose a significant risk to the users.

It should be noted that the non-correction of departures from the requirements of BS 7671 is not an option in a new installation or for the rewire of an existing installation".

 

[telectrix]

thanks lenny. that's cleared up a few myths.

 

[ringer]

You mention 'network circulating currents' in bonding cables. Is there generally current circulating in bonding conductors in PME systems then? I was under the impression that the only time current would flow in bonding conductors would be under fault conditions.

 

[ezzzekiel]

thanks len it was the esc i quoted and additions/ alterations reg in old book but the new one clears it up even better