16mm Earth main protective conductor

[Sav]

Hi everyone,

Just a quick question I hope I can get some advise on.

Saw a 1 bedroom purpose built 1st floor flat last night that is in need of a rewire.

The consumer unit is the old rewire-able type with 16mm T&E on supply side.
Although its red and black on the 16mm, it does look newish (10 years may be), but obvious tests will need to be carried out.

In the basement, which the customer does not have access too ( my FP2 key does not fit either, as it has some kind of security lock), I would have presumed there must be an isolator to this flat, as well as the other 5 flats on this block.
Again, this would need examining when the time comes.

I mentioned to the builder who is going to be carrying out building works, that we must check and upgrade the earthing accordingly, and also bring a 16mm earth to the consumer unit.
His guy, who also does electrics, said that the 16mm T&E along with its 6mm earth is more than adequate.

I have always bought in 16mm earth to the consumer unit, as thats what we were told to do on sites etc.

Am I missing something???

Thanks and regards,
Sav

 

[tony mc]

If his guy is putting his name on the cert let him get on with it.

I would be looking at the earthing arrangement the lenth of run re isolation, is it in need of RCD protection from the basement etc.

IMO More info is required and access to the mains is necessary before you can go any further!

 

[david john cook]

you would expect a switchfuse to be feeding it .access to mains is very important .not only for you ,but everyone else .i went to job a few years back in a similar situation regarding 6mm earth .they had also run a 10mm earth as a parallel earth path .

 

[Clarkey65]

This sounds like the dreaded adiabatic equation in the regs and my head is hurting already. Seem to remember something along the lines of a BS1361 100 AMP needs a 10MM earth cable i think. Hope this helps.

 

[rich.250]

As above, I think check your required size. You know what's right and wrong then

 

[tony mc]

Its a guessing game as if its PME I am affraid the adiabatic is out of the question.

More info is required!

 

[rich.250]

More guessing....
Would it not be effectively a submain though???

 

[sedgy34]

firstly get access to the incoming main, check and test ZE etc
megger the 16mm supply cable to the said 1 bed flat if ok, fit 60A KMF at incomer to supply 16mm t&e upgrade equipotential bonds, Now carry on with your rewire. :smilewinkgrin:

 

[yellowvanman]

Its a guessing game as if its PME I am affraid the adiabatic is out of the question.

Why? Adiabatic is suitable for all types of supply, when it comes to bonding then thats a different matter!

 

[tony mc]

Its my understanding that you are regulated by table 54.8 when PME conditions apply re the main earth as it will have to be the same or bigger than the bonding conductors.

In this case the op states it is a 6mm earth and if it is PME then the minimum is 10mm if the neutral is 35 mm or less !

 

[yellowvanman]

Its my understanding that you are regulated by table 54.8 when PME conditions apply re the main earth as it will have to be the same or bigger than the bonding conductors.

In this case the op states it is a 6mm earth and if it is PME then the minimum is 10mm if the neutral is 35 mm or less !

I maybe misunderstood your post, in that you were were saying the adiabatic is not relevant for a sub-main supply because pme was used, but I see where you are coming from now! ie wanting to provide bonding in the apartment itself!

 

[Sav]

Hi everyone,
Thanks for all your replies,

Just one thing which I may have not put down properly, is that the 16mm T&E is all thats coming into the consumer unit.
The 6mm is actually part of the T&E.

So its red & black 16mm and 6mm earth in pvc.
There is no additional earth run in parallel, thats why I said run a 16mm from MET (once I can get access to switch room), to consumer unit.

Thanks again and sorry for my stupid writing !!!

Sav

 

[Guitarist]

Hi everyone,


Saw a 1 bedroom purpose built 1st floor flat last night that is in need of a rewire.



His guy, who also does electrics, said that the 16mm T&E along with its 6mm earth is more than adequate.

Thanks and regards,
Sav

Sounds like sour grapes to me. Whatever you say will probably be wrong in his eyes.

 

[Guest55]

Your builder is right , as a sub-mains to the flat , the earth in the T&E cable is fine.
The only earth that needs to be 16mm is the conductor from the MET to the switchgear at the supply position.

 

[Guest55]

I maybe misunderstood your post, in that you were were saying the adiabatic is not relevant for a sub-main supply because pme was used, but I see where you are coming from now! ie wanting to provide bonding in the apartment itself!

The apartment wont need a protective bonding conductor unless the water or gas mains enters the building in this flat.

 

[Sav]

Your builder is right , as a sub-mains to the flat , the earth in the T&E cable is fine.
The only earth that needs to be 16mm is the conductor from the MET to the switchgear at the supply position.

Thanks Biff and sorry again if I didnt explain myself properly.
So just to confirm, 16mm from MET to isolator (which I presume there is one).
Thanks again and have a great weekend,
Sav

 

[Geoffsd]

The apartment wont need a protective bonding conductor unless the water or gas mains enters the building in this flat.

Post isn't about bonding but each flat should have its own bonding to where the supply enters the flat.

 

[Guest55]

Post isn't about bonding but each flat should have its own bonding to where the supply enters the flat.

But he doesnt need to run a separate 16mm earth to each flat to do that , which is what Sav was suggesting.

 

[Geoffsd]

But he doesnt need to run a separate 16mm earth to each flat to do that , which is what Sav was suggesting.

I didn't say he did.

You said

"The apartment wont need a protective bonding conductor unless the water or gas mains enters the building in this flat."

which is wrong.

 

[Guest55]

no im not lol.
what your suggesting is supplementary bondng , the protective bonding to the gas and water mains has to be connected back to the MET , which wont be in the flat.

 

[PC Electrics]

The cpc in the distribution circuit must be sized for the most onerous requirement to be made of it. Now if this DC was supplying a garage with no other services then the 6mm cpc in the t&e would be perfectly adequate as it would be fed from a 63A MCB or an 80A fuse.

However, each flat is a seperate dwelling in this instance and will have other services (defo water and maybe gas). These will need main protective bonding within each dwelling. It is common to bond these services back to the flat CU. If the supply in the basement is TN-C-S / PME, then the bonding must be 10mm back to MET, thus the 6mm cpc will not be adequate. In this case a parallel 10mm will be required.

If the supply is TN-S, then 6mm meets the minimum basic requirement.

In addition, guidance is that the bonding back to MET must be no more than 0.05 ohm. If the flat is several floors up and so the earth conductor is long, then 16 or even 25mm may be required.

IMO it is not accpetable to bond each flats services directly to the MET in the basement, though I know some believe it is.

 

[Geoffsd]

Biff5.

I'm not suggesting anything.

You said

"The apartment wont need a protective bonding conductor unless the water or gas mains enters the building in this flat."

which is wrong.

However, each flat is a seperate dwelling in this instance and will have other services (defo water and maybe gas). These will need main protective bonding within each dwelling. It is common to bond these services back to the flat CU.

 

[Guitarist]

Think you need to get access to the supply mate, then all the conjecture can stop.

 

[Guest55]

The cpc in the distribution circuit must be sized for the most onerous requirement to be made of it. Now if this DC was supplying a garage with no other services then the 6mm cpc in the t&e would be perfectly adequate as it would be fed from a 63A MCB or an 80A fuse.

However, each flat is a seperate dwelling in this instance .
.

But with a shared gas and water main.
Which will be bonded as it enters the building , back to the MET.
And it still wont need a 16mm earth to each flat , which is the point ive tried to make all along.

 

[Geoffsd]

This is important:

You said

"The apartment wont need a protective bonding conductor unless the water or gas mains enters the building in this flat."

which is wrong.

Each flat will also need its own bonding from where the services enter the flat to the flat's MET.

But with a shared gas and water main.
Which will be bonded as it enters the building , back to the MET.

And it still wont need a 16mm earth to each flat , which is the point ive tried to make all along.

Then you shouldn't have called it ​bonding​ nor mentioned the water or gas mains.

 

[Guest55]

The flat wont have a MET , that will be in the basement at the supply position.

And you keep saying im wrong but without producing any facts to support your own statement ?

And why shouldn't i have mentioned the gas / water services ?

Your posts make little sense to be honest.

 

[spark 68]

The

flat wont have a MET , that will be in the basement at the supply position.

No, but it will have an EMT (Earth Marshalling Terminal) in each CU, and as each flat is classed as a seperate installation in it's own right, and this requires it's own local main bonding in each installation (read premises) as per 544.1.2 (BGB).

This is stated specifically in GN8 although the reg number given in GN8 is 537-02-01, as this book is now out of date but until the new updated version comes out this is all we have.

 

[Engineer54]

The flat wont have a MET , that will be in the basement at the supply position.

And you keep saying i'm wrong but without producing any facts to support your own statement ?

And why shouldn't i have mentioned the gas / water services ?

Your posts make little sense to be honest.

I'm afraid you are WRONG!! Each apartment /flat is considered a separate installation, which WILL require it's own bonding arrangements from the flats EMT to both gas and water, and any other extraneous service that enters the apartment/flat. That requirement is regardless of any bonding arrangements at the basements supply position MET...

There is a similar thread running at the moment, i think you NEED to read it, as well as BS7671 and the appropriate Guidance Notes!!!

 

[Guest55]

The

No, but it will have an EMT (Earth Marshalling Terminal) in each CU, and as each flat is classed as a seperate installation in it's own right, and this requires it's own local main bonding in each installation (read pemises) as per 544.1.2 (BGB).

This is stated specifically in GN8 although the reg number given in GN8 is 537-02-01, as this book is now out of date but until the new updated version comes out this is all we have.

Thanks for providing this info and for clarification.
Although classing each flat as a seperate installation when there is only 1 DNO supply , only 1 gas main and only 1 water main is open to debate in my mind.

 

[tony mc]

The

No, but it will have an EMT (Earth Marshalling Terminal) in each CU, and as each flat is classed as a seperate installation in it's own right, and this requires it's own local main bonding in each installation (read pemises) as per 544.1.2 (BGB).

This is stated specifically in GN8 although the reg number given in GN8 is 537-02-01, as this book is now out of date but until the new updated version comes out this is all we have.

Thats the problem with GN8 it takes a while to find out what the new reg number is!

 

[Top Cat]

Wow! I was going to reply to original post but i don't think i will now after all the arguments!

 

[spark 68]

I have added the two pages from GN8 to my previous post #27 to clarify

 

[Guest55]

So , taking onboard recent comments....
What size should this protective bonding conductor in the flat be ?
Just out of interest ...

 

[tony mc]

At the moment we do not know the earthing arrangement of the premises.

If its PME then table 54.8 comes into play re the bonding and if TNS or TT the csa should be not less than half the csa of the required earthing conductor with a min of 6mm!

 

[spark 68]

According to GN8, the main bonding is sized to the DNO's incoming Neutral supply cable, not the downstream local neutral supply cable to the individual flat, it should not be less than 35mm in the case of PME supplies.
It is a little odd in the the main bonding conductors can have a greater csa than the local Live supply (to each flat CU) conductors.

In all other cases (TT, TNS) the main bonding is sized to be not less than half of the Earthing conductor.

At least that is how I read it (GN8).

 

[Engineer54]

Thanks for providing this info and for clarification.
Although classing each flat as a seperate installation when there is only 1 DNO supply , only 1 gas main and only 1 water main is open to debate in my mind.

NO, ... There is nothing to debate at all!!

 

[Guest55]

At the moment we do not know the earthing arrangement of the premises.

If its PME then table 54.8 comes into play re the bonding and if TNS or TT the csa should be not less than half the csa of the required earthing conductor with a min of 6mm!

Agreed , but table 54.8 applies to the main protective bonding ,which is in the basement , where the gas and water services enter the building.
Not relevent to where the services enter each flat.
Unless your suggesting that there needs to be 2 sets of main protective bonding conductors , basement and flat ?


I do like a healthy technical debate lol.

 

[Guest55]

NO, ... There is nothing to debate at all!!

A very narrow minded view you've got there.

 

[spark 68]

But each flat has it's own main bonding requirement.

I will be glad when the new GN8 comes out, as it is a nightmare trying to marry up the 16th ed reg no's with the current regs.

 

[spark 68]

To Add,

If each flat is PME, the earthing conductor to each flat has to be a minimum of 35mm, (again sized to the DNO's incoming Neutral), as it has to satisfy as a combined CPC and main bonding conductor (Pg 52 GN8).

 

[Engineer54]

This is getting to be like pulling teeth...lol!!

Every flat, (be there 2 or 20 flats) will each require a main protective bonding installation, REGARDLESS of the main protective bonding arrangements made at the buildings service head and main distribution centre and where the main services enter the building (eg, gas & water).

 

[tony mc]

Agreed , but table 54.8 applies to the main protective bonding ,which is in the basement , where the gas and water services enter the building.
Not relevent to where the services enter each flat.
Unless your suggesting that there needs to be 2 sets of main protective bonding conductors , basement and flat ?


I do like a healthy technical debate lol.

Main protective bonding conductors are required in every flat in Multi Occupancy Premises regardless to what is connected outside that premises!

 

[Engineer54]

A very narrow minded view you've got there.

Really, perhaps you can tell us what's narrow minded about following requirements??

And if you think about it, why it's a requirement!!!

 

[Guest55]

To Add,

If each flat is PME, the earthing conductor to each flat has to be a minimum of 35mm, (again sized to the DNO's incoming Neutral), as it has to satisfy as a combined CPC and main bonding conductor (Pg 52 GN8).

But the flats aren't pme , tt , tns or anything else , they're supplied via a privately
owned sub-mains ? so not entirely relevent.

 

[Guest55]

Really, perhaps you can tell us what's narrow minded about following requirements??

And if you think about it, why it's a requirement!!!

I didnt say the requirements were narrow minded , just your view that an wider issue cant be discussed openly.

 

[spark 68]

But the flats aren't pme , tt , tns or anything else , they're supplied via a privately
owned sub-mains ? so not entirely relevent.

But they must have an earthing system, and depending what this is, determines what cable sizes are used, and each flat still has to have local main bonding fitted regardless of anything else.

 

[Engineer54]

I didn't say the requirements were narrow minded , just your view that an wider issue cant be discussed openly.

That's just my point, ...What Wider Issue is there to discuss??

But the flats aren'time , tt , tns or anything else , they're supplied via a privately
owned sub-mains ? so not entirely irrelevant.

Doesn't matter who is supplying the power into this block of apartment, the earthing arrangement is going to be one of three earthing systems. Earthing systems are not just the domain of being DNO supplied....

But whatever the system is and whoever supplies the power, BS7671 will still govern the requirements of all such domestic electrical installations in the UK!!

 

[Guest55]

The only earthing each flat has is the circuit protective conductor contained within the 16mm T&E cable.
Surely you would size your bonding requirements for the flats from the 16mm and not the size of the supply tails in the basement ?

Not entirely straightforward is it lol?

 

[sedgy34]

can i be referee lol

 

[spark 68]

Surely you would size your bonding requirements for the flats from the 16mm and not the size of the supply tails in the basement ?

Except where PME conditions apply (I don't like the word 'Export') :devilish: