Bonding Gas Supply in an Outbuilding

[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

 

[GEOFF S]

Hi Guys
It's the OP here! Fascinating and thought provoking discussion, not entirely clear.
FYI
1. The installation is PME
2. The SWA cable is XLPE 3 core, not 4.
3. I used a C3 with NICEIC Technical Support's blessing
4. My table gives the equivalent Cu size of the armour as 7.39 sqmm. Is that correct?
5. Under PME rules, I understand that the CPC should be 10mm. Is that correct?
6. As neither the core nor the wire armour are individually 10mm, is it your conclusion that they may be combined? If so, how do you calculate their combined Cu value?

Cheers
Pete

1, Okay
2, Okay
3, Okay
4 That depends upon what k factors you have used, as a general rule you take the aromuring to be at 10 C less than the Line, so 60C.
4,The CPC? Do you mean Earthing conductor or Main protectine Bonding?
5, If PME, there is a risk of divereted neutral current circulating in the armour, this creates a heating effect I2R and can effect the Temp of other conductors contained within the cable. Can you use seperate the armour and a core to meet the requirements, the regs allow this!
6, You may struggle to convince your inspector to accept anthing different than equivalent conductance, so use a ratio of 8-1.


Spark68, do you have a regulation number which states

the regs say we cannot combine them, different materials

Cheers

 

[TJ Anderson]

If I drive round there and bond it myself for free can we end this post lol

 

[davesparks]

The ratio given for copper:steel is 1:8.5 in GN8, it also gives the ratio for aluminium but I don't know it off the top of my head

 

[Piratepete]

If I drive round there and bond it myself for free can we end this post lol

Yeah. Ok. I'll shut up now. At some time I'll have to go round and install a 10 mm bonding wire between the outbuilding and the house. I'm thinking that an overhead one would be easiest. Any rules against that?:biggrin:
Cheers
Pete

 

[spark 68]

Spark68, do you have a regulation number which states

Cheers

Oh! god not again, you cannot split the functional requirements of a single protective conductor across different materials.

In this case
Armour complies to equivalent 10mm copper = fine
core complies to 10mm = fine

Neither complies not fine

the other parts of that section

Armour complies as CPC and core complies with bonding conductor = fine
core complies as CPC and armour complies with bonding (if not causing heating) = fine

Neither comply on their own = not fine ie. cannot be combined to make up csa, they do not conduct nor current share equally.

I believe there was an article in wiring matters about this a while back, read the regs table 54.8 for PME, don't just pick one reg in isolation, you have to take that section together, failing that look at GN8

 

[TJ Anderson]

Yeah. Ok. I'll shut up now. At some time I'll have to go round and install a 10 mm bonding wire between the outbuilding and the house. I'm thinking that an overhead one would be easiest. Any rules against that?:biggrin:
Cheers
Pete

It would be handy for drying laundry I suppose

 

[TJ Anderson]

No you're a baiter....

Weird.... I heard you were a master at that!!

 

[GEOFF S]

The ratio given for copper:steel is 1:8.5 in GN8, it also gives the ratio for aluminium but I don't know it off the top of my head

Some even quote 9, It can vary quite considerably, copper wire isnt that pure and becomes less conductive and when you realise what it is you are trying to acheive it becomes a little arbitrary.

Cheers

 

[GEOFF S]

Oh! god not again, you cannot split the functional requirements of a single protective conductor across different materials.

In this case
Armour complies to equivalent 10mm copper = fine
core complies to 10mm = fine

Neither complies not fine

the other parts of that section

Armour complies as CPC and core complies with bonding conductor = fine
core complies as CPC and armour complies with bonding (if not causing heating) = fine

Neither comply on their own = not fine ie. cannot be combined to make up csa, they do not conduct nor current share equally.

I believe there was an article in wiring matters about this a while back, read the regs table 54.8 for PME, don't just pick one reg in isolation, you have to take that section together, failing that look at GN8

So how is it you can use an individual core of the swa(copper) and the armour(steel) together as a cpc?


Cheers

 

[spark 68]

So how is it you can use an individual core of the swa(copper) and the armour(steel) together as a cpc?


Cheers

Arghh! we don't, either the core complies, OR the armourings comply for a "straight" CPC, that is what we have been saying, the armourings are earthed for protective reasons where a core is used as the CPC, NOT to make up the csa.

Sometimes we use a core for a bonding conductor, and the armourings as the CPC, so long as both comply csa wise for their respective functions, ie. as two separate protective conductors, both (in their own right) fulfilling two different roles.

 

[davesparks]

Sometimes we use a core for a bonding conductor, and the armourings as the CPC, so long as both comply csa wise for their respective functions, ie. as two separate protective conductors, both (in their own right) fulfilling two different roles.

Wtf? How do you prevent them both fulfilling both functions? They'll be connected together at both ends.

 

[HandySparks]

Wtf? How do you prevent them both fulfilling both functions? They'll be connected together at both ends.

Signpost at the ends: "<--- CPC Electrons This Way / Bonding Electrons This Way --->". :biggrin:

 

[spark 68]

Wtf? How do you prevent them both fulfilling both functions? They'll be connected together at both ends.

They may well be physically connected, but need to be assessed for compliance individually, as in the OPs case in this long thread, the armourings may well comply as a CPC, but not as a MPB, so ideally he would need a 10mm core to fulfil the MPB part, this is what you yourself were putting forward when I looked up that iffy table.

 

[GEOFF S]

Going back some now but im pretty sure mines and quarys required more stringent impedances to keep touch voltages down, some of the strands in the amouring were copper?

Or am i getting confused.

Cheers

 

[davesparks]

They may well be physically connected, but need to be assessed for compliance individually, as in the OPs case in this long thread, the armourings may well comply as a CPC, but not as a MPB, so ideally he would need a 10mm core to fulfil the MPB part, this is what you yourself were putting forward when I looked up that iffy table.

That is not what I was putting forward earlier, what was saying earlier was that the main bond should not be made up of multiple conductors added together.

The 10mm core would become the cpc and the main bond by default, the armour would only need bonding at one end, but could be connected at both to improve the cpc.