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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.
Discuss Bonding Gas Supply in an Outbuilding in the UK Electrical Forum area at ElectriciansForums.net
Read my text. I'm querying the sub-main earth size, not main bonding.
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.
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.
Chaps, I'll just bring your attention to the fact that 543 applies to Protective Conductors only, NOT Protective Bonding Conductors, that's 544.
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...
Chaps, I'll just bring your attention to the fact that 543 applies to Protective Conductors only, NOT Protective Bonding Conductors, that's 544.
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!!
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
I disagree, and there are issues, see 543.2.5
I dont have the regs to hand, could you expand?
Cheers
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