S.W.A. Armour Earthing.

davezawadi (David Stone):

The filler or bedding layer is outside the conductors to provide a smooth surface for the armour to lay on and has nothing to do with the sheath. If it were not there the armour would be variously corrugated and might damage the conductor insulation if the cable is moved. It ensures that all the armour strands are exactly the same length and thus can move freely. I pointed out why sheaths are not considered insulating above, it is because cables pass through a cooling water bath after extrusion which is used to also test that the insulation is complete with an insulation test. The sheath cannot be tested separately and so cannot be guaranteed to be complete, although it is rarely defective. Simple. I suppose the SWA sheath could be tested in the same way but I believe that it is not.


There is another point about the armour too, why would you not use this as the CPC? In sizes up to I thtink 95mm always has at least as much corrected cross section as the conductors, so is very suitable. I know that SWA in 3 core is often cheaper than the 2 core version, but this is not a reason to use the spare core as CPC, you would bet better off paralleling one of the live conductors fro reduced volt drop.

The outer black sheath is robust enough to withstand abrasion and penetration  by sharp stones and pebbles in most cases, although a suitable sand layer is better for a buried S.W.A. cable. The outer sheath keeps out water thus preventing the cable from becoming a water pipe thus transporting water from a higher to a lower level enclosure. It also prevents water from eventually damaging the steel wire armour, despite the galvanisation, it will still rot over time I have found. I am happy to consider the tough black outer P.V.C. sheath as an insulator.


Z.

davezawadi (David Stone):

The filler or bedding layer is outside the conductors to provide a smooth surface for the armour to lay on and has nothing to do with the sheath. If it were not there the armour would be variously corrugated and might damage the conductor insulation if the cable is moved. It ensures that all the armour strands are exactly the same length and thus can move freely. I pointed out why sheaths are not considered insulating above, it is because cables pass through a cooling water bath after extrusion which is used to also test that the insulation is complete with an insulation test. The sheath cannot be tested separately and so cannot be guaranteed to be complete, although it is rarely defective. Simple. I suppose the SWA sheath could be tested in the same way but I believe that it is not.


There is another point about the armour too, why would you not use this as the CPC? In sizes up to I thtink 95mm always has at least as much corrected cross section as the conductors, so is very suitable. I know that SWA in 3 core is often cheaper than the 2 core version, but this is not a reason to use the spare core as CPC, you would bet better off paralleling one of the live conductors fro reduced volt drop.

The outer black sheath is robust enough to withstand abrasion and penetration  by sharp stones and pebbles in most cases, although a suitable sand layer is better for a buried S.W.A. cable. The outer sheath keeps out water thus preventing the cable from becoming a water pipe thus transporting water from a higher to a lower level enclosure. It also prevents water from eventually damaging the steel wire armour, despite the galvanisation, it will still rot over time I have found. I am happy to consider the tough black outer P.V.C. sheath as an insulator.


Z.