@Dustydazzler
It's funny I nearly suggested that option above but didn't know how it would go down on here so kept quiet, I have been known to do that in the past, don't really see anything wrong with it personally!
It's funny I nearly suggested that option above but didn't know how it would go down on here so kept quiet, I have been known to do that in the past, don't really see anything wrong with it personally!
D
Dustydazzler
It is better than what most builders do which is to trim off half the cores so it fits
It suggests the conductor is oversized to enable suitable termination as per manufacturer recommendations. You have also divided the conductor into separate unequal csas.
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I think the OP means that the SWA has a core used as cpc, and the SWA gland/banjo has a lead connected to it, giving two separate wires which should go to the same terminal on the CU earth bar. These two wires might go into the terminal individually, but the two together are too big.
I would connect the SWA core to the correct terminal, and the banjo flylead to a spare amongst the bonding terminals.
Common sense has to take priority over the letter of the regs occasionally.
I would connect the SWA core to the correct terminal, and the banjo flylead to a spare amongst the bonding terminals.
Common sense has to take priority over the letter of the regs occasionally.
How would it be half. Assuming this is a seven strand conductor the split is 43% and 57% so not half which effectively results in parallel conductors of differing csa.
10mm or 10m it makes little difference in essence. BS7671 states parallel conductors shall be of the same csa and length, fault current or overcurrent will not think this is only 10mm so it should be fine.
It does indeed, but over two terminals with mm between them even with a 43-57 split of probably 10mm or so maximum is it really going to cause an issue. Whilst I agree that it not best practice and as I suggested earlier a pin lug would be the best option, when In a fix it is a practical solution, and as Dusty says better than giving the conductor a haircut.
If you use an SWA cable with 1 core and the armor both used as earth then there will be a difference in the size of earth conductor for the whole circuit and unequal current under fault can flow.
It may well not cause an issue but it creates parallel conductors of differing csa the length is not relevant. The suggestion of a swa core and sheath is totally different.
I realise this isn't the main point of the thread - but while we are having confessionals asking hypothetical questions, in the situation where the CPC bar has run out of adequate terminals is it permitted to connect a new earthing conductor the same csa as the main earthing conductor with a ring terminal crimp onto main earth connection, and run this outside the CU to an external Kingsmill bar with more ring terminals, which are then in turn used for the problem new circuit that doesn't fit inside?
@timhoward
I think that is a practical solution and see no real issue with it as long as they are big enough to be sufficient for mechanical protection and they are identified for the circuits they protect.
I think that is a practical solution and see no real issue with it as long as they are big enough to be sufficient for mechanical protection and they are identified for the circuits they protect.
Terminating four strands of a 7-strand conductor in one terminal and three in another does not equate to creating parallel conductors in the conventional sense. Two paralleled cores of a cable need to be equal to ensure predictable current sharing where the CCC and adiabatic fault withstand capability are determined by the thermal and electrical characteristics of the cable. Within 10mm of the terminal bar, the thermal characteristics of the bar swamp those of the cable, while the electrical characteristics of the main cable length swamp those of the termination. Therefore provided both terminations are sound and can be relied upon to remain sound, the split termination will be 'better' than all conductors in one hole because both the electrical and thermal contact resistance are likely to be lower.
Notice I am not referencing the regulations here, only the physics.
Notice I am not referencing the regulations here, only the physics.
the voice of reason speaks. my tuppence worth is that you have a copper core cpc and a steel armour also as cpc. their respective resistances can never be the same, so the same size argument can't be applied. tin hat firmly wedged over lug holes.
If the copper cable is able to meet all limits for adiabatic, etc, on its own then you don't have to consider the parallel SWA there.
Of course if you have a SWA-fault then it will have to deal with the fault current but typically it will be OK as most SWA armour does meet the adiabatic limit, and in the cases where it does not so you need the copper CPC, then if both ends of armour on the copper CPC then again probably OK as fault current has sort-of two paths on the armour to return.
Surely the regs concerned with unequal parallel earth paths are intended to be applied where one or both of the cpcs is undersized from being able to safely carry the full fault current on its own.
In this case, where the parallel earths are a full size SWA core and the SWA armour/banjo tail, and both should be designed for the full fault current, then the unequal length argument is irrelevant.
Edit: I wrote this post without having seen pc1966's post above, as a result of having severe internet drop outs for the last month. It appears my post is echoing his.
In this case, where the parallel earths are a full size SWA core and the SWA armour/banjo tail, and both should be designed for the full fault current, then the unequal length argument is irrelevant.
Edit: I wrote this post without having seen pc1966's post above, as a result of having severe internet drop outs for the last month. It appears my post is echoing his.
I think this thread has been talking about two different things at the same time, as @westward10 noted:
Somewhere en-route we assumed it was a more classic scenario of running out of large enough terminals on the CPC bar and we started talking about the merits (and regulations/physics) regarding splitting the 7 strands between two terminals. But I don't think this was the main point.
The OP was talking about the sheath and core as far as I can tell.
Somewhere en-route we assumed it was a more classic scenario of running out of large enough terminals on the CPC bar and we started talking about the merits (and regulations/physics) regarding splitting the 7 strands between two terminals. But I don't think this was the main point.
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