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

 

[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:

 

[johnboy6083]

I would argue that if a fault were to appear in the system, then your bonding within the flat needs to be sized according to the largest possible current that could appear, in order to keep the touch voltage to a minimum. This is a lot nmore prevelant in PME supplies, where you could have neutral currents appearing on your metalwork, from other installations outside your own. This is why the PME bonding requirements are more stringent.

 

[malcolmsanford]

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?

It is Biff Table 54.8 calls it the Supply Neutral which is the Neutral provided by the supplier and reg 544.1.1 when talking about sizing non PME supplies refers to the Installation earthing conductor

Look up the definitions for Supplier and Installation they are 2 different animals mate

 

[Guest55]

^^^Good answer lol

Well ive enjoyed the debate greatly.
Its good to hear the views of others.
I hope my good natured attempt at playing devils advocate hasnt been lost on some of you.

 

[Engineer54]

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

You don't need to use the word ''Export'' in this circumstance, or any instance where you are carrying a bonding conductor with a sub-main etc, outside of an existing extraneous zone to connect to a new installation (say a garage) with an extraneous earth, ...As your then ''Extending'' the existing extraneous Zone, not Exporting it ..lol!!!

 

[GLENNSPARK]

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.

so lets take a garage for instance.....would you not extend the equepotential zone out to extranious conductive parts within said garage on a PME even though the service head isn`t within that garage and both gas and water services originate from within the house?

 

[GLENNSPARK]

You don't need to use the word ''Export'' in this circumstance, or any instance where you are carrying a bonding conductor with a sub-main etc, outside of an existing extraneous zone to connect to a new installation (say a garage) with an extraneous earth, ...As your then ''Extending'' the existing extraneous Zone, not Exporting it ..lol!!!

you beat me to it eng...lol....i`d posted mine before reading this.....

 

[Guest55]

so lets take a garage for instance.....would you not extend the equepotential zone out to extranious conductive parts within said garage on a PME even though the service head isn`t within that garage and both gas and water services originate from within the house?

But the flats are contained within the same building as the supply intake -
your example is of a external building remote to the mains / services.
they differ on that respect.

 

[GLENNSPARK]

but theres still the risk of differing potentials being introduced here due to corrosion of extrainious pipework and/or someone coming along with john guests....as both water and gas will be coming into EACH seperate flat.....it will need to be kept at the same potential as any exposed conductive parts within those flats..(class 1s) for instance....

 

[GLENNSPARK]

But the flats are contained within the same building as the supply intake -
your example is of a external building remote to the mains / services.
they differ on that respect.

but my example was of EXTENDING the equepotential zone.....so would that not include in this case..extending the equepotential zone out to individual flats within the fabric of that building?....dont lose sight of what "extending the equepotential zone" means Biff....

 

[spark 68]

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

I was being slightly sarcastic in that post Glenn (Devil emoticon on the end), due to many past arguments on here, I would have used the word 'Extend' myself.