multiple cores for same circuit?

[hawkal]

some plonker ordered and installed the wrong swa cable (too many cores not enough csa) but honestly the csa issue is only due to voltage drop. So I was wondering your opinions on using multiple cores together as parallel conductors? I've looked at the regs and it looks okay but I may have missed something.

 

[spark 68]

It is allowed, see reg 523.8, they should have equal loading, have same csa etc..etc..

 

[Jimmyb]

I end up doing it alot on farms due to long runs. usally tie wrap the cores together then tape with correct colours

 

[Darkwood]

It is allowed, see reg 523.8, they should have equal loading, have same csa etc..etc..

It is allowed but be careful with SWA as i assume its 4core thus you are using the swa as the earth so effectively the armouring will have to relate to a combined conductor size when working out if it is big enough to satisfy the earthing requirements and may require additional earth wire run if not, its not a straight forward yes or no as cable size, core no', temp rating etc all need to be evaluated before you can give a yes answer with a reg' no, your advice although not intensionally could be misleading.

 

[spark 68]

Something else I realised after posting, is if they are SWA multicore, you would have to keep the 'doubled up' conductors within the same cable/sheath, and be careful with the phasing, eddies and all that.

 

[Darkwood]

Something else I realised after posting, is if they are SWA multicore, you would have to keep the 'doubled up' conductors within the same cable/sheath, and be careful with the phasing, eddies and all that.

Think you missed the O/P's idea, although it all assumption he said he had too many cores so im guessing hes running a 4core swa with a single phase supply of which he wants to combine the 4cores into doubled up 2core cable, this is fine as long as he works out the csa of the armouring in relation to any core X 2 to see if it complies, you lost me on the phasing and eddie current bit??

 

[spark 68]

you lost me on the phasing and eddie current bit??

I had another look at the reg 523.8, and it goes on to mention singles in trefoil or flat formation, and then I thought (conjecture at this point) for a moment if the OP was thinking of doubling up conductors, and ended up with seperate phases, or seperate Line and Neutral in different SWA sheaths (seperate ferrous enclosures), this may not permissable.

I wasn't too concerned about thermal considerations as the OP said it was just for VD and not CCC reasons.
Point taken about just quoting a reg though.

 

[Engineer54]

It is allowed but be careful with SWA as i assume its 4core thus you are using the swa as the earth so effectively the armouring will have to relate to a combined conductor size when working out if it is big enough to satisfy the earthing requirements and may require additional earth wire run if not, its not a straight forward yes or no as cable size, core no', temp rating etc all need to be evaluated before you can give a yes answer with a reg' no, your advice although not intensionally could be misleading.

If this is a 4 core SWA cable and is being used as a 2 core cable then it would be unlikely that the CSA of the SWA will not be sufficient, as the CSA of that armour will be far greater than on a 2 core SWA...

Far better to sleeve these cores with the correct colour than to use PVC tape, that has a habit of loosing its stickiness for want of a better word...lol!!

 

[Darkwood]

i understand why you said it but O/P has given the impression of just one SWA been used with more cores in it than he initially needs but due to it not complying because of volts drop he wants to combine the cores which would suggest 1 SWA having 4cores effectively running as 2cores by combining them thus single phase, no mention of multiple phases or cables, i agree with your point on seperate ferrous enclosures but if it was 3phase he could just run a same sized cable along the same route in effect 2 SWA's run in parallel and only joint like for like at their termination points then each cable carries approx 50% load and still will maintain a balance to omit any eddie currents. Yes if you run neutral down one SWA and line down the other it will give rise to eddie currents and possible overheating ... well unless you used aluminium glanding plates.
As goes the thermal reference; i was meaning the temp rating of the cable as it will give a different k2 value for 70 degrees than 90 degrees which will be required to work out the compliance of the swa as an earth.

 

[Engineer54]

i understand why you said it but O/P has given the impression of just one SWA been used with more cores in it than he initially needs but due to it not complying because of volts drop he wants to combine the cores which would suggest 1 SWA having 4cores effectively running as 2cores by combining them thus single phase, no mention of multiple phases or cables, i agree with your point on seperate ferrous enclosures but if it was 3phase he could just run a same sized cable along the same route in effect 2 SWA's run in parallel and only joint like for like at their termination points then each cable carries approx 50% load and still will maintain a balance to omit any eddie currents. Yes if you run neutral down one SWA and line down the other it will give rise to eddie currents and possible overheating ... well unless you used aluminium glanding plates.
As goes the thermal reference; i was meaning the temp rating of the cable as it will give a different k2 value for 70 degrees than 90 degrees which will be required to work out the compliance of the swa as an earth.

That's not quite true, ...with cables passing in excess of around 250A, Aluminium starts losing it's ability to stop circulating currents. Always better to use non metallic glanding plates in these situations... I always change main switchboard non ferrous glanding plates on my projects for 6 to 8mm paxolin board or equivalent.

 

[hawkal]

Thanks for the input everyone.

 

[Knobhead]

That's not quite true, ...with cables passing in excess of around 250A, Aluminium starts losing it's ability to stop circulating currents. Always better to use non metallic glanding plates in these situations... I always change main switchboard non ferrous glanding plates on my projects for 6 to 8mm paxolin board or equivalent.

I’ve always had to use steel gland plates due to M&Q regs. So for singles I would slot them like this and then fill the slots with epoxy to keep creepy crawlies out.

View attachment 9076

I didn’t know about aluminium failing at high currents, makes you wonder about all the aluminium glands used. I used brass, which was fine until a contractor replaced the nice brass locknuts with steel. Just glad I wasn’t around when the transformer went bang.

 

[Darkwood]

That's not quite true, ...with cables passing in excess of around 250A, Aluminium starts losing it's ability to stop circulating currents. Always better to use non metallic glanding plates in these situations... I always change main switchboard non ferrous glanding plates on my projects for 6 to 8mm paxolin board or equivalent.

Thx for the pointer, yes somewhere in the back of my mind i recall it did have a high current failure point but was only passing fleeting comment with regards to the O/P question where all pointers indicate a average situation, but happy to stand corrected.... paxolin is the bee's knees in choice.