16mm Earth main protective conductor

[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.

 

[Guest55]

please close the thread.....lol
I've been beaten down by at least 6 members....
at least i went down with a fight. :2guns:

 

[spark 68]

please close the thread.....lol
I've been beaten down by at least 6 members....

These type of threads are one of the best for debating things, as you get to see someone elses point of view, and/or interpretation of the regs, and often a different perspective on things, most importantly we learn things from these debates, as none of us know it all.

 

[Guitarist]

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).

That's a big earth cable...

 

[GLENNSPARK]

please close the thread.....lol
I've been beaten down by at least 6 members....
at least i went down with a fight. :2guns:

as spark 68 Biff.....no one`s tryin to beat anyone down here mate...its a thread with differing views.......its important that the correct method/procedure is employed in regards to bonding as its about keeping potential differences to a minimum....as you well know......but the beauty of debate is all about getting several different inputs..then coming to a decisive decision based on those inputs....and this will usually end up being the correct course of action to take.....

 

[spark 68]

That's a big earth cable...

Thats what GN8 appears to suggest => 35mm squared for the combined earthing conductor (depending on CSA of supply Neutral) and bonding from the incoming MET to the EMT, and 35mm bonding conductors (page 52, fig. 5.16, GN8), the drawing on this page shows seperate buildings, but page 53, multi-occupancy buildings refers you back to the same regs. also see page 50 GN8.

The drawing on page 53 fig. 5.17, is a little unclear, as this shows two seperate PME links with a CNE rising service, which seems to suggest a PEN conductor, which I thought was forbidden for use (except by the DNO/Distributor), unless someone else would like to shed some further light on that drawing ?

Edit: a closer look at fig. 5.17 shows that the incoming DB belongs to the DNO/Distributor, so that explains that.

 

[spark 68]

After realising that the drawing 5.17 on page 53 GN8 is a CNE rising service by the DNO (PME supply), this then suggests that the local main bonding conductors (in each flat) could then be 10mm, subject to the individual supply Neutral (PEN conductor) CSA to each flat., as each flat would have it's own seperate supply and supply fuse in the distributors DB, also each flat would have it's own CNE/PME link.

This is certainly an interesting subject.

 

[Guitarist]

Ty for investigating that spark. I need to do some extra reading-up myself if I'm honest.

 

[Sav]

Ok, Here goes.

Managed to get the door open to the main intake room in the basement.

So, its a TN-S system. The gas meters are all lined up one after another, but there is no earth within the 600mm. Its actually connected from just when it leaves the basement (they are all like that).
So what I did, is run my 10mm earth from "our" side of the gas meter to the MET.
The water though (there is only one water mains into the building), is on the other side of the basement, access ok, but again no earth. So again, I ran a 10mm earth from "our" side of the water to the MET. The gas is approx 2.5 meters from the MET and the water approx 3 meters from the MET.

The tails that go into the meter for the flat that I am working on are the old red/black 16mm tails and then from the meter 16mm red / black into a wylex 60 amp BS1361 isolator. From there its in PVC 16mm red/black with the 6mm earth to the consumer unit. So its 16mm twin and 6mm earth in pvc, not armoured etc.

The isolator is not earthed, so I am going to run a 10mm earth from the isolator back to the MET. Its only 1 meter away from the MET.

Apart from the supply tails to the meter being 16mm, does everything else sound ok, or do you suggest anything else that is required.
Thanks again,
Sav

 

[rich.250]

If the tails are feeding a 60 switch fuse and a meter long the 16mm tails can stay.

 

[Guest55]

^^^ exactly as i expected to be.

snigger ;-)

All sounds well now you've bonded the services.
And where the hell were you sav during my mammoth debate ?
lol.

 

[Sav]

^^^ exactly as i expected to be.

snigger ;-)

All sounds well now you've bonded the services.
And where the hell were you sav during my mammoth debate ?
lol.

Biff, I am really really thankful to you all for your help and assistance.
Sorry I left you alone, but believe me, I was reading the threads whilst looking at the BRB, On Site Guide and all the books I could get my hands on.

I am so lucky that I have the privilege of having you guys around and its like having my own tutor and mentor.

I cant thank you enough and I hope that one day I will have half the knowledge you all have and that would be good enough for me.

Again apologies if my post was a no brainer and just to warn you, I will be asking more questions as time goes by, as I make notes with each of your replies, which again help me.

You are all superstars and thanks once again,
Sav

 

[Guest55]

No sweat , topics on earthing and rcds always provide lively debate.

 

[Geoffsd]

So, its a TN-S system. The gas meters are all lined up one after another, but there is no earth within the 600mm. Its actually connected from just when it leaves the basement (they are all like that).
So what I did, is run my 10mm earth from "our" side of the gas meter to the MET.
The water though (there is only one water mains into the building), is on the other side of the basement, access ok, but again no earth. So again, I ran a 10mm earth from "our" side of the water to the MET. The gas is approx 2.5 meters from the MET and the water approx 3 meters from the MET.

This is bonding not earthing but correctly done.