Hi Wozz,
Yes, you can get aluminium armored, which so far as i know would prevent "circulating currents" but you would still have the problem of it going into enclosures. Might have been DC circuits perhaps??
Hi Badger,
"but yet the dno are allowed to use concentric cable which effectively creates a single core armoued type cable, although it has the neutral on the outer cores/sheath if pme'd or tncs then the outer sheth part is at earth potential / neutral potential anyway, so therefore no difference in single core armoured"
The concentric stuff might have a single "core" if you like, but it is still TWO conductors grouped together. In a single phase one, the current runs down the middle, and back up the surrounding "concentric" bit, so it is still a pair of conductors "in action" if you like as a pair, which is the important bit in avoiding undesirable electromagnetic effects. In an "ordinary" single core SWA cable, [unlike the DNO service cables] presumably the concentric armour does not carry any current under "normal" fault free conditions, so it is just one conductor "on its own" as it were.
In a three phase concentric service cable, the outer concentric bit may or may not carry and load depending on phase balance, but the other conductors are still all grouped together and in action at the same time.
If the three phase service cable feeds a load on just one phase, then the concentric neutral will then start carrying current, and we are back to a pair of conductors running together!!
john..
Yes, you can get aluminium armored, which so far as i know would prevent "circulating currents" but you would still have the problem of it going into enclosures. Might have been DC circuits perhaps??
Hi Badger,
"but yet the dno are allowed to use concentric cable which effectively creates a single core armoued type cable, although it has the neutral on the outer cores/sheath if pme'd or tncs then the outer sheth part is at earth potential / neutral potential anyway, so therefore no difference in single core armoured"
The concentric stuff might have a single "core" if you like, but it is still TWO conductors grouped together. In a single phase one, the current runs down the middle, and back up the surrounding "concentric" bit, so it is still a pair of conductors "in action" if you like as a pair, which is the important bit in avoiding undesirable electromagnetic effects. In an "ordinary" single core SWA cable, [unlike the DNO service cables] presumably the concentric armour does not carry any current under "normal" fault free conditions, so it is just one conductor "on its own" as it were.
In a three phase concentric service cable, the outer concentric bit may or may not carry and load depending on phase balance, but the other conductors are still all grouped together and in action at the same time.
If the three phase service cable feeds a load on just one phase, then the concentric neutral will then start carrying current, and we are back to a pair of conductors running together!!
john..