Extraneous conductive parts in outbuildings

[soulman]

Hi, i am after a bit of advice. I went to a property which had 3 outbuilding, all were separate from the main building, one garage, one shed, & a workshop. Circuits all supplied from main building. Earthing system is TT. In all of the 3 outbuilding there is a separate water supply with metallic pipes. There is one socket outlet & one light in each building.

My question is, should these pipes be supplementary bonded? or would they need m.p.b to the MET.

cheers

 

[Badged01]

Not wanting to steal anyones thunder, I'll pass on this question and await appropriate responses .......

 

[D Skelton]

Are the metallic water supplies extraneous? They might seem metallic but they're often fed in plastic. If they are extraneous, are they continuos from the main building to the outbuildings? If they are, are they bonded at the main building?

A few different scenarios and solutions here:

1. The water pipes are not extraneous - They need no bonding.

2. The water pipes are extraneous and are not already bonded (for example a completely seperate water supply or there is plastic between the main building and the outbuilding but enough copper in the ground to make them extraneous) - They need bonding back to the MET at the main building if you are extending the equipotential zone or bondng back to the outhouse MET is you are creating a TT system.

3. The water pipes are extraneous but they are effectively connected to earth already via the MET at the main building - They need no additional bonding, however supplementary bonding may be prudent.

 

[trev]

The only way to know is to test them to see if they are actually ECPs.

 

[soulman]

Yes they are definately ECP. They are connected to the main building & the main building has mpb.
The circuits are protected by 30ma rcd.

 

[D Skelton]

You need to do two things.

First, disconnect the main earthing conductor from the MET at the main building and test between the incoming water pipe and the main earthing conductor. This will determine whether it is extraneous, anything less than 45,000 ohms and it is.

Second, with the main earth still disconnected, long lead test between the water pipe at the outbuilding and the incoming water at the main building (remember to null the lead!), anything around 0.05 ohms or less and it is effectively connected to earth throughout its entire length.

If the incoming water pipe at the outbuilding is effectively connected to earth, no further bonding is required, however I would personally still add supplementary bonding at the outbuilding.

 

[mechelec]

Not wanting to steal anyones thunder, I'll pass on this question and await appropriate responses .......

??????????????????? If you know the answer say so. Don't be shy.

 

[spark 68]

There should be still MPB installed at each building locally, to an EMET (411.3.1.2) applies (taken from GN8), providing it is an ECP of course.

 

[Richard Burns]

You need to do two things.

First, disconnect the main earthing conductor from the MET at the main building and test between the incoming water pipe and the main earthing conductor. This will determine whether it is extraneous, anything less than 45,000 ohms and it is.

With the 45KΩ you are aiming for a 5mA safe current, what is the basis of this level of current?
Perception is lower and let go is higher, is this just a very safe level?

 

[spark 68]

Here you go Soulman, that is the basic gist of it

 

[jamie-spark]

That's the way I like it

 

[jamie-spark]

If it comes in building A say in metallic and goes out in metallic there are two points to bond in building A alone. Then there is the other buildings that will require further bondage

 

[Hawkmoon]

If it comes in building A say in metallic and goes out in metallic there are two points to bond in building A alone. Then there is the other buildings that will require further bondage

Why bond it twice?

 

[Engineer54]

If the incoming water pipe at the outbuilding is effectively connected to earth, no further bonding is required, however I would personally still add supplementary bonding at the outbuilding.

You'd be a bloody fool not to bond any metallic extraneous earth entering a stand alone building, whether it had been bonded at say the main house or another building or not!!. Call it whatever you like supplementary bonding, main bonding or whatever!!

Same goes for blocks of flats, every flat should be classed as a separate entity, as far as main bonding of extraneous metal pipework etc is concerned....

 

[Richard Burns]

If an earth potential is introduce to the building because a metallic service enters then it should be bonded.
If the metallic service later passes into the ground again as it leaves the building it is also introducing an earth potential at that point and so should be bonded there.
However if it is continuous I would not bother, but if someone replaces some of the internal pipework with plastic then there could be problems.

Perhaps

 

[jamie-spark]

Why bond it twice?

When mr wet head comes in and does alternations in plastic. Two extraneous parts.

What do the regs say ? Point of entry to the building,which end is the entry ?

 

[jamie-spark]

I know what u are thinking multiple steels in ground ( large industrial buildings ) effectively connected together, and only one bonding conductor.

 

[Hawkmoon]

When mr wet head comes in and does alternations in plastic. Two extraneous parts.

What do the regs say ? Point of entry to building which end is the entry ?

Yeah, take your point - with future plumbers intent on 'spoiling' things lol, that would probably be wise.

 

[soulman]

Hi, I have managed to find my GN8. The separate buildings ECP do require main protective bonding back to the MET in the main building. I thought supplementary bonding would suffice, but the book says not.

Thanks for your help.

P.s Cheers to spark 68

 

[D Skelton]

You'd be a bloody fool not to bond any metallic extraneous earth entering a stand alone building, whether it had been bonded at say the main house or another building or not!!. Call it whatever you like supplementary bonding, main bonding or whatever!!

Same goes for blocks of flats, every flat should be classed as a separate entity, as far as main bonding of extraneous metal pipework etc is concerned....

Well that was kind of my point lol.

It would be supplementary if already bonded and yes, you would be a fool not to IMHO

 

[D Skelton]

With the 45KΩ you are aiming for a 5mA safe current, what is the basis of this level of current?
Perception is lower and let go is higher, is this just a very safe level?

10mA is seldom likely to prove fatal to a human, it is also said to be the let go threshold. 5mA is never going to prove fatal to a human unless applied directly across the heart and will not cause involuntary muscle contraction.

There are no hard and fast rules when it comes to determining a safe level of shock current but this is the value I was taught to work to and I still do.

 

[Engineer54]

Well that was kind of my point lol.

It would be supplementary if already bonded and yes, you would be a fool not to IMHO

Well as in this case of separate buildings, any extraneous metal pipe or other metalwork entering a building, would actually require bonding, i wouldn't necessarily be calling that bonding supplementary either.

 

[D Skelton]

Well as in this case of separate buildings, any extraneous metal pipe or other metalwork entering a building, would actually require bonding, i wouldn't necessarily be calling that bonding supplementary either.

Technically it is supplementary as it is in addition to. Bonding is required between the MET and each extraneous conductive part within the installation. If the installation is formed of multiple buildings then this requirement has to be applied to each seperate building of the installation. IMHO it still wouldn't be main bonding though as you would be installing supplementary bonding to the same requirements of the main bonding in the main building. This is my take on it anyway, but we're arguing semantics here though and it all hinges on definitions not being clearly defined and our interpretation of the word 'supplementary'.

The main point though has been addressed, and that is that bonding should be installed at the outbuildings if there are extraneous conductive parts present.

 

[Engineer54]

In the case of extraneous metallic water/gas pipes entering a building whether those pipes are continuous or not, and virtually all will be. The fact that they are entering the building from the ground should mean that it would be main bonding because no-one can guarantee that pipework will not be altered in the future by insertion upstream of plastic piping, which means it will be imperative that main bonding of that extraneous pipework via the buildings EMT back to the MET is carried out.

Which was not wholly what you were stating in post #3 and #6 of this thread. The same reasoning applies to multi occupancy buildings, eg, blocks of flats etc. Semantics it might be, but an important issue, that's best done right, just same...

 

[D Skelton]

That's why I was saying I would supplementary bond at the outbuildings, but I'm not too proud to be corrected on my interpretation of my definition. All that said, we're still singing from the same hymn sheet as the reason I would bond is because of the very reasons you have stated.

With regards to multiple dwellings within one building, I view them as being one installation in one building, therefore my interpretation would mean that you only needed to bond the once rather than at each dwelling, although personally, I would still bond at each dwelling. I may stand to be corrected on this also.

 

[spark 68]

If you look at the GN8 diagram, it only shows the MPB path, it even says that the supply (to the outbuildings) cables CPC "may" also fulfil this role (depending on min csa etc.).

Another thing not shown on that diagram is that all the CPCs for that out/building would also be required to be connected to the EMT, or EMB (Earth marshalling Bar) on that drawing.

Exactly the same as you would for flats and the like, so I am sure that just bonding straight back to the MET at the origin is not what is intended, more to create an equipotential zone in each building is what is required.

I have only added this just for completeness, not aimed at anyone in particular.

 

[Silly Sausage]

There's a row of 15 old terraced houses, each with lead water pipes entering each one, presumably fed off the same water main.
You're called out to carry out some electrical work at one of the properties, which one is irrelevant.
You find on initial inspection that there is no main bonding in place.

I'll let you finish this off Mr Skelton!

 

[Engineer54]

If you look at the GN8 diagram, it only shows the MPB path, it even says that the supply (to the outbuildings) cables CPC "may" also fulfil this role (depending on min csa etc.).

Another thing not shown on that diagram is that all the CPCs for that out/building would also be required to be connected to the EMT, or EMB (Earth marshalling Bar) on that drawing.

Exactly the same as you would for flats and the like, so I am sure that just bonding straight back to the MET at the origin is not what is intended, more to create an equipotential zone in each building is what is required.

I have only added this just for completeness, not aimed at anyone in particular.

It's not, as you say, each flat is classed as a separate installation in it's own right, and has it's own equipotential zone, connected to the flats MET, which in reality is a building EMT, that is then connected via the flat's incoming supply tails/cable back to the buildings MET!!

 

[D Skelton]

There's a row of 15 old terraced houses, each with lead water pipes entering each one, presumably fed off the same water main.
You're called out to carry out some electrical work at one of the properties, which one is irrelevant.
You find on initial inspection that there is no main bonding in place.

I'll let you finish this off Mr Skelton!

Put main bonding in

 

[Engineer54]

That's why I was saying I would supplementary bond at the outbuildings, but I'm not too proud to be corrected on my interpretation of my definition. All that said, we're still singing from the same hymn sheet as the reason I would bond is because of the very reasons you have stated.

With regards to multiple dwellings within one building, I view them as being one installation in one building, therefore my interpretation would mean that you only needed to bond the once rather than at each dwelling, although personally, I would still bond at each dwelling. I may stand to be corrected on this also.

Sorry, but yes you need to be corrected on this one too i'm afraid!!...lol!!

 

[spark 68]

It's not, as you say, each flat is classed as a separate installation in it's own right, and has it's own equipotential zone, connected to the flats MET, which in reality is a building EMT, that is then connected via the flat's incoming supply tails/cable back to the buildings MET!!

Yes I know that E54 lol, just the diagram is not that clear, and could be somewhat misleading by the way it is drawn I just added some clarification, even the text in GN8 is not very clear. lol

 

[D Skelton]

Sorry, but yes you need to be corrected on this one too i'm afraid!!...lol!!

Can you clarify?

IMHO, until the meaning of the words 'building' and 'electrical installation' are clearly defined in the regs, the answer is about as clear as mud lol.

Does the introduction of a meter in what is essentially a submain for all intents and purposes split an installation in two?

 

[Geoffsd]

Each flat may classed by the regulations as a separate installation but in reality they are not, are they?
They may have been converted from what used to be one house.

Although 'main bonding' in each flat is required, this is in fact, as has been said, 'supplementary' much the same as a house's garage fitted with a separate CU and water pipe from the house.

Isn't the requirement to main bond each flat merely because it may be uncertain whether the real main bond is satisfactory and to save hunting for it?

 

[D Skelton]

Each flat may classed by the regulations as a separate installation but in reality they are not, are they?
They may have been converted from what used to be one house.

Are they though, this is my point, because from what I see, there is no clear definition of what an electrical installation actually is, where it starts and where it ends? I would go further and suggest that not only in reality are they not seperate electrical installations, but that they are not even defined as such in any regulation whatsoever?!

Although 'main bonding' in each flat is required

As above, is it???

I would do it, but out of nothing more than caution. It states clearly that bonding needs to be applied in seperate buildings, which as we agree on is techically supplementary, but it says nothing about seperately occupied spaces within the same building, metered or not???

The words 'grey' and 'area' spring to mind!

 

[spark 68]

GN8 gives some guidance wrt flats, each *installation* should have it's own bonding arrangement, the picture example given in GN8 shows offices, however the same would apply to individual flats.

It tells you that this would equally apply to seperate installations in a multi-occupancy building.

Edit: the other scenario would be where you had one supply/Origin with sub-mains then this would follow the same scheme as given earlier for multiple buildings served by one supply, of course there is scope for other variations, I suppose the basic idea is to create an equipotential zone in each dwelling/installation.

 

[Geoffsd]

Are they though, this is my point, because from what I see, there is no clear definition of what an electrical installation actually is, where it starts and where it ends? I would go further and suggest that not only in reality are they not seperate electrical installations, but that they are not even defined as such in any regulation whatsoever?!

Confused - I thought I was agreeing with you.

As above, is it???
I would do it, but out of nothing more than caution. It states clearly that bonding needs to be applied in seperate buildings, which as we agree on is techically supplementary, but it says nothing about seperately occupied spaces within the same building, metered or not???

Isn't the word - premises. 544.1.2

So, it depends what now are 'premises'.

I would consider flats or offices to be separate premises.

 

[D Skelton]

GN8 gives some guidance wrt flats, each *installation* should have it's own bonding arrangement, the picture example given in GN8 shows offices, however the same would apply to individual flats.

It tells you that this would equally apply to seperate installations in a multi-occupancy building.

It gives guidance yes, but it is also trying to make 'clear' something that is not. Quite rightly it says that "It is clear that BS 7671 requires bonding in each installation" because this is clear, but then it goes on to say "And this would equally apply to seperate installations of a multiple occupancy building".

Well hang on a minute there.. It still hasn't defined what an electrical installation actually is, where it starts, or where it ends. It points out that the origin of an installation is where electrical energy is delivered to an electrical installation, but where is the point of delivery? At the meter? At the service head? At the TX?

The fact remains, it is not clear, and I know that GN8 has tried to make sense of it, but it simply doesn't cut the mustard in my mind I'm afraid. Like I said, I would always install bonding in a seperate occupied space within one building, but could I condemn someone for not doing so? Hmm, I'm not so sure I could.

I remember discussing this very issue a few years back with a very qualified engineer, his answer was essentially "cover your ar$e!". He also rambled on a bit about the IEE and how they couldn't organise a pi$$ up in a brewery, let alone write a book. I wouldn't go that far personally, but I can sure as hell see where he was coming from!

 

[spark 68]

Edit: the other scenario would be where you had one supply/Origin with sub-mains then this would follow the same scheme as given earlier for multiple buildings served by one supply, of course there is scope for other variations, I suppose the basic idea is to create an equipotential zone in each dwelling/installation.

I was editing the previous post, I agree that GN8 does not quite clear the waters much,

 

[D Skelton]

Confused - I thought I was agreeing with you.


Isn't the word - premises. 544.1.2

So, it depends what now are 'premises'.

I would consider flats or offices to be separate premises.

Haha, we are agreeing, I was just pointing out that even though we are agreeing, the regs are even vaguer still!

The Oxford English Dictionary defines the word 'premises' as a house or building. Just thought I'd point that out to muddy the water even further

 

[spark 68]

Ha ha, that is why I used the word "dwelling". lol

 

[Engineer54]

Can you clarify?

IMHO, until the meaning of the words 'building' and 'electrical installation' are clearly defined in the regs, the answer is about as clear as mud lol.

Does the introduction of a meter in what is essentially a submain for all intents and purposes split an installation in two?

I don't worry about what the Reg's define, i think it comes down to commonsense and what you want to achieve and why...

Yep, ....basically anytime the pipework (or any other metalwork) enters a building or a dwelling in a multi dwelling building that is bringing with it an extraneous means of earth, then bonding is required whether it has been bonded elsewhere on the installation or not. The introduction of a meter basically just denotes a boundary within a multi dwelling building. IMO essential to main bond service pipework and the like, as it enters that boundary, as the occupier has no control over what happens to any service pipework outside of he's boundary lines....

In the case of multi dwellings installations, this is especially the case where the fabric of the building can introduce extraneous elements to metallic service pipes etc, such as concrete framed and floored constructions....

In latter years this is less of a potential problem due to the prolific use of non metallic service and internal pipework. But can and will continue to cause problems to existing metal pipework, where sections are being converted to non metallic.

We are only talking about simple domestic stuff here, i can assure you it get's far, far more complicated when it comes to hospitals (with their many piped services) and say heavy industrial installations, where there are many service metal pipeworks that pass through several buildings....

 

[Guest55]

some stuff..............

whos been a naughty boy then ?

are you the same skelton electrical thats been arguing and insulting OMS on the IET forum ??

tsk tsk. ;-)

 

[D Skelton]

I don't worry about what the Reg's define, i think it comes down to commonsense and what you want to achieve and why...

Yep, ....basically anytime the pipework (or any other metalwork) enters a building or a dwelling in a multi dwelling building that is bringing with it an extraneous means of earth, then bonding is required whether it has been bonded elsewhere on the installation or not. The introduction of a meter basically just denotes a boundary within a multi dwelling building. IMO essential to main bond service pipework and the like, as it enters that boundary, as the occupier has no control over what happens to any service pipework outside of he's boundary lines....

In the case of multi dwellings installations, this is especially the case where the fabric of the building can introduce extraneous elements to metallic service pipes etc, such as concrete framed and floored constructions....

In latter years this is less of a potential problem due to the prolific use of non metallic service and internal pipework. But can and will continue to cause problems to existing metal pipework, where sections are being converted to non metallic.

We are only talking about simple domestic stuff here, i can assure you it get's far, far more complicated when it comes to hospitals (with their many piped services) and say heavy industrial installations, where there are many service metal pipeworks that pass through several buildings....

I agree with much of what you say, but the problem is, you cannot treat 'common sense' or opinion as a requirement. Common sense would be the reason I would install bonding to each individual occupied space within a building but I cannot see that it is actually required, therefore I wouldn't be telling others that it is required. I'd be pointing them in the direction of all the relevant regulations and telling them to interpret it for themselves.

The bit I do disagree on is hospitals and larger industrial installations being harder when there are several services passing through several buildings. I would argue that they are easier than say an office block or block of flats because the regs are clear about the requirements for bonding having to be met at each seperate building to all extraneous conductive parts whereas the regs are far from clear when it comes to a multiple occupancy building.

 

[D Skelton]

whos been a naughty boy then ?

are you the same skelton electrical thats been arguing and insulting OMS on the IET forum ??

tsk tsk. ;-)

Oh lordy, we mustn't question OMS, he's right about EVERYTHING you know!

 

[Guest55]

Oh lordy, we mustn't question OMS, he's right about EVERYTHING you know!

unfortunately he's probably gonna tear you a new --- in many tech debates most days of the week.

its just a fact of life theres always a bigger fish...............
;-)

 

[D Skelton]

unfortunately he's probably gonna tear you a new --- in many tech debates most days of the week.

its just a fact of life theres always a bigger fish...............
;-)

For sure! The fella definitely knows his stuff! But on that one point, he's wrong, and unlike many others on that forum with their tongues up his a$$, I ain't afraid to say it!

 

[Engineer54]

I agree with much of what you say, but the problem is, you cannot treat 'common sense' or opinion as a requirement. Common sense would be the reason I would install bonding to each individual occupied space within a building but I cannot see that it is actually required, therefore I wouldn't be telling others that it is required. I'd be pointing them in the direction of all the relevant regulations and telling them to interpret it for themselves.

The bit I do disagree on is hospitals and larger industrial installations being harder when there are several services passing through several buildings. I would argue that they are easier than say an office block or block of flats because the regs are clear about the requirements for bonding having to be met at each seperate building to all extraneous conductive parts whereas the regs are far from clear when it comes to a multiple occupancy building.

Commonsense combined with sound reasons, i would argue, make far more sense than any unclear requirements. But i would also argue that as far as i can see, it is a requirement to conduct main bonding in each dwelling of a multi occupancy building, and with good reason for doing so too.

There are far more regulations/requirements with regards to bonding certain medical and other services within a hospital complex it ain't just a matter of main bonding at one point on the system, of that i can assure you. So what does BS7671 actually say about the requirements of service pipework, that service as well as pass through several buildings??

 

[D Skelton]

Commonsense combined with sound reasons, i would argue, make far more sense than any unclear requirements.

For sure!

But i would also argue that as far as i can see, it is a requirement to conduct main bonding in each dwelling of a multi occupancy building, and with good reason for doing so too.

I wouldn't go that far, but I can definitely see where you're coming from

There are far more regulations/requirements with regards to bonding certain medical and other services within a hospital complex it ain't just a matter of main bonding at one point on the system, of that i can assure you. So what does BS7671 actually say about the requirements of service pipework, that service as well as pass through several buildings??

And that is exactly my point, the fact that there are clear requirements makes this easier. I am aware of many of the different requirements in other types of installation and most of that is down to clarity.

My main point being, the regs are clear when it comes to multiple buildings whether that be hospitals, campuses, farms or the garden shed, they aint so clear when it comes to multiple occupied spaces within one building.

 

[Engineer54]

For sure! The fella definitely knows his stuff! But on that one point, he's wrong, and unlike many others on that forum with their tongues up his a$$, I ain't afraid to say it!

Tut tut, who you been upsetting now?? If it's not our mates in the sun lounge it's others on another forum...lol!!

 

[GLENNSPARK]

Tut tut, who you been upsetting now?? If it's not our mates in the sun lounge it's others on another forum...lol!!

you trying to say pink handcuffs was Mr Skelton all along?...