Bonding Gas Supply in an Outbuilding

[Deleted member 26818]

I take it no one bothered to google the definition then?
BS7671 requires us to bond any conductive part which enters the building from outside, which may introduce a difference in potential.
There is no requirement to bond conductive parts that do not enter the building from outside.
The plastic water pipe is not conductive, so does not require bonding.
The internal copper water pipes are conductive, but as they do not enter the building from outside, they cannot introduce a difference in potential, and therefore also do not require bonding.

 

[TJ Anderson]

I take it no one bothered to google the definition then?
BS7671 requires us to bond any conductive part which enters the building from outside, which may introduce a difference in potential.
There is no requirement to bond conductive parts that do not enter the building from outside.
The plastic water pipe is not conductive, so does not require bonding.
The internal copper water pipes are conductive, but as they do not enter the building from outside, they cannot introduce a difference in potential, and therefore also do not require bonding.

I quoted the definition in previous post. What difference does it make if it becomes extraneous within the building or outside. If conductive pipework was buried in the floor of the house it could become extraneous.

 

[Deleted member 26818]

I quoted the definition in previous post. What difference does it make if it becomes extraneous within the building or outside. If conductive pipework was buried in the floor of the house it could become extraneous.

You quoted the definition of an extraneous-conductive part, not the definition of extraneous.
It doesn't make any difference, as it's physically impossible for something that is entirely inside a building to also be extraneous.
If the copper pipework were buried in the ground, then the part that is in the ground (no longer inside the building) would be extraneous, and where the copper pipework re-entered the building would require bonding.
However as far as I'm aware, the copper pipework does not exit then re-enter the building.

 

[Geordie Spark]

Twenty three HOURS and fifty four posts later and you're all still arguing about this bloody copper pipe!!

How long would it have taken to find out by testing the damned thing with a meter & long bit of wire???

and it's you lot who think plumbers are a bit mentally challenged!! :laugh:

 

[Engineer54]

Staying with the OP's outbuilding installation, if the metal water pipework that's fed/connected to a incoming plastic pipe, enters the slab internally, say to supply something on the other side of the room it would be prudent to test for being extraneous. Which is going to be pretty certain that it will be, especially if it's been tied to the slabs rebar grid, and therefore will require main bonding. If however it's just been visibly clipped internally to the walls, it's unlikely that it will be extraneous and main bonding will not be required.

The incoming gas pipe goes without saying, will be an extraneous conductive part that will require main bonding...

And that just about clears everything up as far as these two services are concerned with this OP's outbuilding query!!!

 

[Knobhead]

Twenty three HOURS and fifty four posts later and you're all still arguing about this bloody copper pipe!!

How long would it have taken to find out by testing the damned thing with a meter & long bit of wire???

and it's you lot who think plumbers are a bit mentally challenged!! :laugh:

This is the tilers forum! What do you expect?

 

[Knobhead]

The IET mandarins must be howling with laughter at the farce they’ve created!

Bring back the 15th.
Non of this is it, isn’t it, slap a bit of wire on it then it isn’t.

From the OED

Irrelevant or unrelated to the subject being dealt with: one is obliged to wade through many pages of extraneous material.

 

[richy3333]

Whoever did this was either confused or trying to make sure 'belt and braces' style. The incomer for the water before the stopcock is plastic. The floor it passes through is chipboard and the pipe drops down into a solem/void (timber building raised up on blocks). After the stopcock and meter it's all copper either clipped to joists or in stud walls.

 

[shanky887614]

View attachment 28056
Whoever did this was either confused or trying to make sure 'belt and braces' style. The incomer for the water before the stopcock is plastic. The floor it passes through is chipboard and the pipe drops down into a solem/void (timber building raised up on blocks). After the stopcock and meter it's all copper either clipped to joists or in stud walls.

nothing wrong with belt and braces, i wear them when its cold (attached to my sellopets)

 

[Geordie Spark]

This is the tilers forum! What do you expect?

I know it is!!

I'm still trying to work that one out!

 

[Piratepete]

Thanks for your entertaining and informative (some) replies. Rather gobsmacked to see this continue for 5 pages!:angel_smile:

Pete

 

[Piratepete]

NO, it doesn't negate main bonding to the outbuildings CU (EMT) especially if the supply is PME, in which case the sub-main earth should be a minimum of 10mm....

Why should the sub-main earth be a minimum of 10mm? Doesn't table 54.7 apply for a PME supply? Also Table 4.4 (clearer) in the On Site Guide. 6mm supply 6mm earth. Or have I missed something?
Cheers
Pete

 

[Leesparkykent]

Why should the sub-main earth be a minimum of 10mm? Doesn't table 54.7 apply for a PME supply? Also Table 4.4 (clearer) in the On Site Guide. 6mm supply 6mm earth. Or have I missed something?
Cheers
Pete

Have a look at Regulation 543.1.1 and 544.1.1

 

[Des 56]

Thanks for your entertaining and informative (some) replies. Rather gobsmacked to see this continue for 5 pages!:angel_smile:

Pete

Sorry Pete but it seems that even after those 5 pages Leespakykent is still providing info you don't seem to twig

 

[davesparks]

Why should the sub-main earth be a minimum of 10mm? Doesn't table 54.7 apply for a PME supply? Also Table 4.4 (clearer) in the On Site Guide. 6mm supply 6mm earth. Or have I missed something?
Cheers
Pete

Minimum size of a main bond on a PME supply is 10mm. Main bonds must be sized according to the incoming service not for the size of any submains.

 

[Piratepete]

Minimum size of a main bond on a PME supply is 10mm. Main bonds must be sized according to the incoming service not for the size of any submains.

Read my text. I'm querying the sub-main earth size, not main bonding.

 

[Piratepete]

Have a look at Regulation 543.1.1 and 544.1.1

I've looked. where does it say min 10mm? As this section of the regs is a nightmare of cross references, please read the whole of section 4.4 in the On Site Guide and table 4.4(i) in particular.
There is a minumum size, 10mm, for main protective bonding but for the Earthing conductor it is 6mm where 'buried and protected against corrosion and mechanical damage'.

 

[spark 68]

Read my text. I'm querying the sub-main earth size, not main bonding.

The point being made is that if bonding is required at the remote end of the sub-main, then that sub-main's CPC will be required to be sized to act as both a CPC and a main bonding conductor, which means the sub-mains CPC will need to be 10mm minimum to satisfy the PME regs.

 

[Leesparkykent]

But the whole purpose of this thread is about bonding the gas supply in an out building.
If you connect your 10mm bond to the EMT in the outbuilding then the CPC in the cable feeding the sub board in the outbuilding will have to be adequate to comply with the minimum CSA of the bond to the gas. For example it's no good having a 6mm 3core SWA feeding the sub board in the outbuilding when you are required to bond the gas in the out building in 10mm (if it's TNC-S), The CPC in the sub main cable would have to Adequately sized for the bond as well.

 

[Leesparkykent]

The point being made is that if bonding is required at the remote end of the sub-main, then that sub-main's CPC will be required to be sized to act as both a CPC and a main bonding conductor, which means the sub-mains CPC will need to be 10mm minimum to satisfy the PME regs.

I was trying to write the same thing but it took me nearly 10mins lol so didn't see your post.

 

[Piratepete]

But the whole purpose of this thread is about bonding the gas supply in an out building.
If you connect your 10mm bond to the EMT in the outbuilding then the CPC in the cable feeding the sub board in the outbuilding will have to be adequate to comply with the minimum CSA of the bond to the gas. For example it's no good having a 6mm 3core SWA feeding the sub board in the outbuilding when you are required to bond the gas in the out building in 10mm (if it's TNC-S), The CPC in the sub main cable would have to Adequately sized for the bond as well.

Ok. I can see where you're coming from, but can you please explain the application of the first 2 columns in table 4.4 On Site Guide?

 

[Leesparkykent]

Ok. I can see where you're coming from, but can you please explain the application of the first 2 columns in table 4.4 On Site Guide?

Sorry mate haven't got the OSG near me, would have to look later unless someone else can point you in the right direction.

 

[spark 68]

Ok. I can see where you're coming from, but can you please explain the application of the first 2 columns in table 4.4 On Site Guide?

What is there to explain ?

As you go down those first two columns in 4.4 (i) it gives the minimum sizes according to function of said conductor, obviously if it is only an EC then the minimum size is given, likewise for a MPB, where it is used as both functions again the minimum size is given, so a combined EC and MPB then the minimum size for the MPB is used (or whichever is the larger minimum size to satisfy that particular requirement/s), the last row in that table refers specifically to PME/TNC-S, as that table covers both TNS an TNC-S systems, table 4.4 (ii) being for TT

 

[telectrix]

Ok. I can see where you're coming from, but can you please explain the application of the first 2 columns in table 4.4 On Site Guide?

you will not see 4mm, 6mm, or even 10mm for supply live conductors in the normal course of your travels.

 

[Piratepete]

What is there to explain ?

As you go down those first two columns in 4.4 (i) it gives the minimum sizes according to function of said conductor, obviously if it is only an EC then the minimum size is given, likewise for a MPB, where it is used as both functions again the minimum size is given, so a combined EC and MPB then the minimum size for the MPB is used (or whichever is the larger minimum size to satisfy that particular requirement/s), the last row in that table refers specifically to PME/TNC-S, as that table covers both TNS an TNC-S systems, table 4.4 (ii) being for TT

Yes, it's obvious. Mea culpa! I assume there is a statement somewhere about a combined EC and MPB, but then if I'd used my brain.... I was thinking technically.

The CU in this outbuilding is from a 32Amp 6kA MCB in the house CU via a 6mm 3core SWA cable. Main Bonding (min 10mm) is required to the gas and water installations in the outbuilding. Technically, a 6mm earth will easily carry the maximum fault current of the installation. The regs would require the main earth to be 10mm, just because the minimum bonding size you are allowed is 10mm. So on an EICR would this count as a C3 or would you not even bother mentioning it? IMHO i don't see this as a C1 or C2. (Shoot me down again!)

 

[Des 56]

The lack of main bonding to a service?
Have a look for guidance (ie the esc or whatever its called lately)as to the code,that is until your experience allows you to answer these questions when you do start carrying out Eicrs in the future

 

[Leesparkykent]

http://www.electricalsafetyfirst.org.uk/mediafile/100126678/best-Practice-Guide-4.pdf

Have a read through this but ultimately it's you that decides what code to give to any given situation as you are the inspector and signing the report, this is only a guide.

 

[Piratepete]

The lack of main bonding to a service?
Have a look for guidance (ie the esc or whatever its called lately)as to the code,that is until your experience allows you to answer these questions when you do start carrying out Eicrs in the future

You've misunderstood. The gas and water supplies are now bonded in 10mm. The main earth however is only 6mm. technically this will take any likely fault current (32 amp 6 kA supply). So it doesn't comply with the regs though it's not dangerous IMHO.

 

[Piratepete]

http://www.electricalsafetyfirst.org.uk/mediafile/100126678/best-Practice-Guide-4.pdf

Have a read through this but ultimately it's you that decides what code to give to any given situation as you are the inspector and signing the report, this is only a guide.

Ok. Thanks for your patience. I have the guide. not sure if it'll help. It might require a call to NICEIC Technical Help Line. I think my assessor would give it a C3 but everyone always has a different opinion when it comes to fault codes!
Cheers

 

[spark 68]

Can you not utilise the armourings along with the third core to increase your effective CPC csa ?

You might find it complies after all if this has already been done, I will have a look through the various tables later.

Otherwise just note it on the EICR as per the advice given in the links above

 

[davesparks]

Read my text. I'm querying the sub-main earth size, not main bonding.

If main bonding is required at the outbuilding, which in this case it is, then the submain cpc also is a main bond and so must meet the 10mm requirement.

 

[davesparks]

Can you not utilise the armourings along with the third core to increase your effective CPC csa ?

You might find it complies after all if this has already been done, I will have a look through the various tables later.

Otherwise just note it on the EICR as per the advice given in the links above

No, the main bond is required to be a single conductor and cannot be made up of smaller conductors combined

 

[TJ Anderson]

No, the main bond is required to be a single conductor and cannot be made up of smaller conductors combined

I'm not aware of anything requiring single conductor only in BS7671. Where does is stipulate this?

 

[spark 68]

No, the main bond is required to be a single conductor and cannot be made up of smaller conductors combined

I'm not aware of anything requiring single conductor only in BS7671. Where does is stipulate this?

I think Dave is referring to reg 543.2.5

Even so, taking 543.2.5 into account, one of my tables for Equal Size Conductor Cables PVC ins. SWA to BS3646, operating at 70 degrees C gives the equivalent copper csa of the armourings for 3 core 6mm[SUP]2[/SUP] SWA as 15mm[SUP]2[/SUP]
If that's the case then the armourings satisfy as a MPB and the 3rd core as the CPC.

 

[TJ Anderson]

I think Dave is referring to reg 543.2.5

Even so, taking 543.2.5 into account, one of my tables for Equal Size Conductor Cables PVC ins. SWA to BS3646, operating at 70 degrees C gives the equivalent copper csa of the armourings for 3 core 6mm[SUP]2[/SUP] SWA as 15mm[SUP]2[/SUP]
If that's the case then the armourings satisfy as a MPB and the 3rd core as the CPC.

543.2.1

(I have quoted the relevant sub sections)

A protective conductor may consist of one or more of the following

(ii) A conductor in a cable
(v) A metal covering, for example, the sheath. screen or armouring of a cable

Going by that, you could use the combination of armour sheath and cable conductor as a main protective bonding conductor.

 

[spark 68]

543.2.1

(I have quoted the relevant sub sections)

A protective conductor may consist of one or more of the following

(ii) A conductor in a cable
(v) A metal covering, for example, the sheath. screen or armouring of a cable

Going by that, you could use the combination of armour sheath and cable conductor as a main protective bonding conductor.

If you look at 543.2.5 though, this refers specifically to the sheath as a protective conductor and must fulfill condition (i) or (ii) of the reg you quoted, I read this that the sheath must be able to satisfy one of the functions of a given protective conductor in it's own right.

If it does, then we can use the 3rd core as another protective conductor, be that a MPB or a CPC, thus utilizing the other parts of the reg 543.2.1

Now the particular table I looked at gives the copper equivalent of a 6mm PVC 3-core swa as 15mm, now normally we use a rule of thumb that steel has 8X less the conductivity of copper size for size, but this depends on the K values used, this I would need to calculate properly to see if that particular table is true.

Edit: what 543.2.5 is basically saying is that you cannot split the function of a given single protective conductor between the sheath and a core, but we could use the sheath as one protective conductor if it complies as such, and the core as another protective conductor likewise so long as it also complies as another protective conductor.

In this particular case we could possibly use the sheath as the MPB, and the 3rd core as the CPC, it might be the case that in another situation it could be the 3rd core as the MPB and the sheath as the CPC.

 

[Silly Sausage]

Chaps, I'll just bring your attention to the fact that 543 applies to Protective Conductors only, NOT Protective Bonding Conductors, that's 544.

 

[spark 68]

Chaps, I'll just bring your attention to the fact that 543 applies to Protective Conductors only, NOT Protective Bonding Conductors, that's 544.

I don't think that matters in this context Archy, the general rules for protective conductors in 543 apply equally to section 544.

Section 544 applies additional conditions regarding minimum sizes to the preceding section, more specifically to bonding conductors.

 

[Engineer54]

If you look at 543.2.5 though, this refers specifically to the sheath as a protective conductor and must fulfill condition (i) or (ii) of the reg you quoted, I read this that the sheath must be able to satisfy one of the functions of a given protective conductor in it's own right.

If it does, then we can use the 3rd core as another protective conductor, be that a MPB or a CPC, thus utilizing the other parts of the reg 543.2.1

Now the particular table I looked at gives the copper equivalent of a 6mm PVC 3-core swa as 15mm, now normally we use a rule of thumb that steel has 8X less the conductivity of copper size for size, but this depends on the K values used, this I would need to calculate properly to see if that particular table is true.

Edit: what 543.2.5 is basically saying is that you cannot split the function of a given single protective conductor between the sheath and a core, but we could use the sheath as one protective conductor if it complies as such, and the core as another protective conductor likewise so long as it also complies as another protective conductor.

In this particular case we could possibly use the sheath as the MPB, and the 3rd core as the CPC, it might be the case that in another situation it could be the 3rd core as the MPB and the sheath as the CPC.

Not sure what table you're looking at, but there is no way 15 mm of steel armour is going to be the equivalent conductance of 6mm copper, no matter what K values are being applied...

A typical CSA of wire armouring for a typical 3 core 6mm SWA cable is 23mm, and requires minimum of 13.6mm for the SWA to comply for CPC compliance...

Agree you cannot combine different CPC conductors of different materials, both conductors must be able to fulfil compliance in it's own right.

Where PME applies, (when bonding is required) the minimum size of 3 Core SWA would need to be 10mm. That by the way, requires a minimum 22.6mm CSA of of steel wire to meet just the cables CPC requirements... Typically it has a CSA of 39mm of steel wire armour...

 

[spark 68]

Not sure what table you're looking at, but there is no way 15 mm of steel armour is going to be the equivalent conductance of 6mm copper, no matter what K values are being applied...

A typical CSA of wire armouring for a typical 3 core 6mm SWA cable is 23mm, and requires minimum of 13.6mm for the SWA to comply for CPC compliance...

Agree you cannot combine different CPC conductors of different materials, both conductors must be able to fulfil compliance in it's own right.

Where PME applies, (when bonding is required) the minimum size of 3 Core SWA would need to be 10mm. That by the way, requires a minimum 22.6mm CSA of of steel wire to meet just the cables CPC requirements... Typically it has a CSA of 39mm of steel wire armour...

No, the copper equivalent was given as 15mm in one table I looked at.

I appreciate that particular table maybe incorrect, and I would need to do the calcs properly, actually I think I got the table from here

If the k values in that table are correct then the armourings could be used as the MPB, with the 6mm core used for the CPC part.

I will attach the table here for you to look at., the figure in (I think it is brown or orange is the copper equivalent)

If I get my paper work finished I will have a closer look at the calcs used.

 

[Engineer54]

Agggggh!! Not that poxy Wirenut table again!! Do yourself a favour spark 68 (and anyone else that still has this table) throw that bloody thing in the bin where it has belonged for years!!

There is very little in that table i would take as correct, the whole thing about this table, is it's inconclusive, misleading and in many respects just plain Wrong!!!

Just get shot of the bloody thing!!

 

[davesparks]

Chaps, I'll just bring your attention to the fact that 543 applies to Protective Conductors only, NOT Protective Bonding Conductors, that's 544.

So what does a section title protective conductors apply to? If it's not protective bonding conductors then it also can't be circuit protective conductors.

 

[spark 68]

Agggggh!! Not that poxy Wirenut table again!! Do yourself a favour spark 68 (and anyone else that still has this table) throw that bloody thing in the bin where it has belonged for years!!

There is very little in that table i would take as correct, the whole thing about this table, is it's inconclusive, misleading and in many respects just plain Wrong!!!

Just get shot of the bloody thing!!

Cheers, E54

TBF I thought that table was a little on the optimistic side ,it is the only one I have that shows the copper equivalent, I have others that show which sizes the SWA are suitable for use as a CPC, I probably got one of those from you.

When I have finished my paperwork I might have a go at the calcs for the hell of it , the OP should really be looking at this, but then again he could just C3 it, if it is not showing any distress etc..etc..

Note to self, do paperwork as and when it comes in, instead of leaving it all to the last minute! lol

 

[GEOFF S]

543.2.1

(I have quoted the relevant sub sections)

A protective conductor may consist of one or more of the following

(ii) A conductor in a cable
(v) A metal covering, for example, the sheath. screen or armouring of a cable

Going by that, you could use the combination of armour sheath and cable conductor as a main protective bonding conductor.

I agree, i see no issues.

Cheers

 

[spark 68]

I agree, i see no issues.

Cheers

I disagree, and there are issues, see 543.2.5

 

[GEOFF S]

I disagree, and there are issues, see 543.2.5

I dont have the regs to hand, could you expand?

Cheers

 

[Leesparkykent]

K1/k2xS=13.5294

k1=115
k2=51
S= 6mm

 

[GEOFF S]

Thanks Lee.

Well i still see no issues.

Cheers

 

[spark 68]

I dont have the regs to hand, could you expand?

Cheers

Then why the blanket statement ?

543.2.5 The metal covering including the sheath (bare or insulated) of a cable, in particular the sheath of a mineral insulated cable, trunking and ducting for electrical purposes and metal conduit, may be used as a protective conductor for the associated circuit, if it satisfies both requirements of items (i) and (ii) of reg 543.2.2

543.2.2 this reg is actually more about switchgear and bus bar trunking etc. but the salient points here are (i) and (ii)

(i) Its electrical continuity shall be assured, by construction or by suitable connection, in such a way as to be protected against mechanical, chemical or electrochemical deterioration.

(ii) Its cross sectional area shall be at least equal to that resulting from 543.1, or verified by test in accordance with the appropriate part of BSEN 61439 series.


What this is basically saying is that if the armouring is of insufficient csa to satisfy its use as a protective conductor, you cannot make up the difference with another undersized protective conductor, either the armouring has to comply on its own for its intended purpose, or the other protective conductor has to comply the same way. as an example of what would not be allowed, consider you need a CPC of say 10mm, and you calculate your armouring works out as a copper equivalent of 6mm, you cannot just add another CPC or core of 4mm to make up the difference, you would need the additional CPC or core to be 10mm on its own.

You can use both where for instance the armouring would comply as a CPC and a core for the MPB purposes, or vice versa.
This is one reason why you sometimes see a 10mm G/Y cable running along side an armoured cable.

 

[Leesparkykent]

SWA, armour equivalent copper - Ted