Bonding Gas Supply in an Outbuilding

[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.

 

[spark 68]

Okay fair enough, I think we are singing from the same hymn sheet here, when designing a sub-main we go through the assessing compliance bit when we are selecting our cables, and no I wouldn't try to make up the csa as a mix.

I was taught that where PME conditions apply that we allow for the worst case, and the CPC should be calculated separate from the MPB, so if the armourings would have been marginal for the MPB (just complying), then either use an extra core for the CPC or if large enough csa the core as the MPB, and use the armourings for the CPC.

I will have to look in the 16th ed and see if there was an actual reg for this, or if my then old boss was just belts and braces.

 

[LeeH]

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.

What's the problem with using the core for both?

 

[davesparks]

What's the problem with using the core for both?

Of course you use a core for both if a core is available, if no core is available then you use the armour for both.

I really don't understand how so many people manage to complicate such a simple issue.

If a submain is required to include a main bond you size the cpc accordingly. You cannot install a seperate conductor and then make one conductor operate as a bond and the other as a cpc, they're joined together at both ends!

 

[Engineer54]

Of course you use a core for both if a core is available, if no core is available then you use the armour for both.

I really don't understand how so many people manage to complicate such a simple issue.

If a submain is required to include a main bond you size the cpc accordingly. You cannot install a separate conductor and then make one conductor operate as a bond and the other as a cpc, they're joined together at both ends!

Just one rather big problem with that, you'd need a 2 core 70mm SWA to provide a near suitable CSA of steel wire to give you the minimum 10mm equivalence of a copper main bonding conductor!!

 

[Dan]

I'm just bumping some threads in the Electrical Forum, don't mind me while I do this, you don't have to respond to them. Although if they are still current topics, and you do wish to reply, you're welcome to. Keep the thread on-topic and make sure you stick to the forum rules though.