6mm Main Bonding on TN-S domestic install

[freedomrun]

TN-S, 60A Main Fuse, 16mm Tails, 16mm Earth.

Question - CU change required & at the moment has 6mm Main Earth Bonding to gas & Water, less than 0.05 Ohms continuity measured & good condition. I'm pretty sure that this 6mm size Main bonding is compliant - just thought i would check if i should be aware of any other issue with leaving this in place. Thanks.

 

[oxocube]

The main earth is oversized, because 10mm would do, in which case 6mm is ok.

It does not strictly comply, because tns main bonding must be at least half the size of the main earth, but it would have to be a real jobsworth to pull you on it.

 

[malcolmsanford]

As OC has said with that 16mm Main Protective conductor you need to fit a 10mm Bonding conductor.

Can you reduce the size of the Main protective conductor?

 

[Chr!s]

The main earth is oversized, because 10mm would do, in which case 6mm is ok.

It does not strictly comply, because tns main bonding must be at least half the size of the main earth, but it would have to be a real jobsworth to pull you on it.

Not quite correct, the bonding needs to be half that REQUIRED for the earthing conductor. If you calculate the earthing conductor requires 6mm via the adiabatic then the bonding need to be half that not what size cable may of been installed.

Regards Chris

 

[oxocube]

Not quite correct, the bonding needs to be half that REQUIRED for the earthing conductor. If you calculate the earthing conductor requires 6mm via the adiabatic then the bonding need to be half that not what size cable may of been installed.

Regards Chris

Your the one thats 'not quite correct' you're saying 4mm will be ok, that is wrong.

See 544.1.1, main bonding not less than half size of main earth and "not less than 6mm"

In this case the tails and main earth are both 16mm, therefore the main earth "should" or "could" be 10mm which makes the 6mm bonding ok.

 

[Chr!s]

Your the one thats 'not quite correct' you're saying 4mm will be ok, that is wrong.

See 544.1.1, main bonding not less than half size of main earth and "not less than 6mm"

In this case the tails and main earth are both 16mm, therefore the main earth "should" or "could" be 10mm which makes the 6mm bonding ok.

Well i assumed that an electrician would be aware of the minimum of 6mm for bonding, so i don't see how im incorrect in what ive stated other than what i assumed was the obvious

So it needs to be half that required for the earthing conductor and no less than 6mm.

Regards Chris

 

[oxocube]

Well i assumed that an electrician would be aware of the minimum of 6mm for bonding, so i don't see how im incorrect in what ive stated other than what i assumed was the obvious

If you calculate the earthing conductor requires 6mm via the adiabatic then the bonding need to be half that not what size cable may of been installed.

Chris remember the first rule of holes 'when you're in one stop digging', we all make mistakes.

 

[telectrix]

however, if it's solid green, you'll need some green and yellow striped paint.rrr:

 

[Chr!s]

What ever OXO, just because i exposed a fundamental flaw in your knowledge. I was just being specific regarding the fact its the required size not the installed as you claimed.

Dont take it to heart, i failed to mention the 6mm minimum, but the op was was going down the same road as yourself and that was the point i addressed.:wink_smile:

Regards Chris

 

[telectrix]

as the dalek said, climbing off the dustbin... " we all make mistakes".

had similar the other week bonding was 7/044 ( think that's right, old imperial measurement, just over 6mm) adiabatic gave 8mm min. for main earthing conductor, so it stayed.

 

[oxocube]

What ever OXO, just because i exposed a fundamental flaw in your knowledge. I was just being specific regarding the fact its the required size not the installed as you claimed.

Dont take it to heart, i failed to mention the 6mm minimum, but the op was was going down the same road as yourself and that was the point i addressed.:wink_smile:

Regards Chris

Amazing, now you're just being plain stupid, how do you dig a hole while standing on your head.

 

[Chr!s]

Amazing, now you're just being plain stupid, how do you dig a hole while standing on your head.

Lol, lots of Yoga.:juggle2:

 

[freedomrun]

Many thanks for the response - this install is TN-S, but would the install still comply if i were to get another of these and it was a domestic TN-C-S arrangement with the same factors applied as my original question?

 

[telectrix]

think you'll find that BS7671 stipulates 10mm bonding for TNC-S.

 

[freedomrun]

Was thinking that was the case on PME system - ok keep in mind when that one comes along. Cheers.

 

[topquark]

think you'll find that BS7671 stipulates 10mm bonding for TNC-S.

Unless the line conductor or neutral conductor is 50mm or 70mm in which case it's 16mm or 25mm respectively.

Sorry, I could resist (must try harder!!!)

 

[telectrix]

is there any of that the pikeys ain't nicked?

 

[freedomrun]

50mm - 70mm on a domestic install - blimey - they must be using industrial ovens !!!!

 

[ezzzekiel]

After a lot of research on this matter it has been drawn to my attention (via ECA and ESC) that minimum 6mm main bonding can stay in place on existing instalations providing they show no signs of damage and are verified adequate, and is left at your discretion but should be noted on the eic.

refered to reg 132.2 (or there abouts dont have regs handy)
ADDITIONS AND ALTERATIONS.
no alterations to properties unless EXISTING bonding and earthing are verified as adequate for the alteration.

 

[oxocube]

and are verified adequate,

How do you do that?

 

[telectrix]

adiabatic.

 

[ezzzekiel]

how would you do it?

check no signs of thermal (or mechanical) damage do continuity test on conductor, check adiabatic Ze, Zs etc then make an informed decision.

this is not a get out of upgrading bonding clause and in my humble opinion it should be carried out when possible.

Also a mention that pme supply must be pre 1988 if existing bonding is to be left in situ to comply with electrical safety regs.

Looked into this as firm i worked for were replacing load of social housing consumer units but didnt want bonding replaced unless needed so wanted something a little more concrete than "my boss told me to do it"

 

[oxocube]

adiabatic.

Adiabatic is not applicable to bonding conductors.

Edit - A light came on and now I see what you're getting at.

 

[ezzzekiel]

im pretty sure tel knows this but there is a relationship between main earthing and bonding conductor sizing....

 

[telectrix]

Adiabatic is not applicable to bonding conductors.

and as ezzie says, use adiabatic to determine required size of main earth, then bonding needs to be not less than 50% of that. (TNC-S notwithstanding)

 

[topquark]

50mm - 70mm on a domestic install - blimey - they must be using industrial ovens !!!!

No one mentioned domestic, it was however was meant in jest as others were being somewhat pedantic about it

 

[freedomrun]

I actually mentioned DOMESTIC in my original post question as this is what the question was refering to.

On a Domestic TN-C-S with a 16mm bonding to the MET, my bonding to Gas and Water services must be 10mm if not mechanically protected?

 

[Octopus]

BS 7671 - 131.8 is worth a read

 

[just add water sparks]

show/hideQ12. When carrying out electrical work on an installation forming part of a TN-C-S system, is it necessary to upgrade existing 6 mm² protective equipotential bonding to 10 mm²?

Not necessarily. If the existing 6 mm² 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 require to be upgraded.

Regulation number(s)

• 132.16
• 544.1.1

Just had similar problem ,researched into threads.The above para taken from the Electricity Saftey Council. Question and Answers page , Alterations.Would appreciate any ones take on this ??? hope there is no stoney silence!!!!!! i take it this refers to the main bonding

 

[atkins_1]

was hoping to find some answers when i searched for this but all i found is a bunch of gits flirting with each other...!!!?!?!?!?!?:willy_nilly:

 

[telectrix]

there's a lot of answers in this thread if you bothered to read it. seeing as how you've made the effort to resurrect it after over 2 years.

 

[i=p/u]

Don't know who's a spark or engineer after reading this whole thread ..

 

[Engineer54]

And i can't see why you would leave a 6mm in place at a time of undertaking a re-wire, ....what to save a couple of quid or so!! It's Nonsense to me!!

 

[richy3333]

^^^ exactly surely a rewire means new cables!?