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Bonding Gas Supply in an Outbuilding

Discuss Bonding Gas Supply in an Outbuilding in the UK Electrical Forum area at ElectriciansForums.net

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Piratepete

Hi Guys
Doing an EICR of a property.
The client has an outbuilding with gas and water supplies. It has it's own CU fed from the main CU in the house.
The water is bonded but the gas is not.
The water supply is underground from the house in plastic and then changes to copper which is bonded.

The gas supply comes from the house in an underground copper pipe linked to the gas pipes in the house. So, electrically, it would be subject to the bonding in the house.
But does this negate the need to bond it in the outbuilding?

Looking forward to wise words!

Cheers
Pete:confused:
 
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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
 
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.
 
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'.
 
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.
 
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.
 
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.
 
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?
 
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
 
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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.
 
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!)
 
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
 
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.
 
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
 
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
 
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
 
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.
 
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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.
 
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.
 
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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.
 
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...
 
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.
 

Attachments

  • SWA CSA COPPER EQUIVALENT.pdf
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