29 Jan 03 21:25
I have yet to see single core SWA cable, I do not think that anybody made it (or would want to make it). Normally single core cables are unarmoured. In my distant past I recall aluminium wire armoured (AWA) single core cables being used on one site. AWA struck as being next to useless. You may well have eddy current problems and maybe circulating current problems in the SWA. Remember, your gland plates would need to be earthed and if you use SWA glands, these will bond the SWA to earth via the gland. Glands normally are brass or aluminium.
Your method of installation (in the trench with removable lids) sounds fine.
Make sure that you select the conductor size based on the worst case part of your run (which sounds to be the bit in the trench that will be covered with sand). Six trefoils of 630mmsq, you must have a big transformer. How many neutrals are you putting in? Some wiring codes will let you have a neutral as small as one third the size of the phase conductors, but you would be well advised to consider a larger neutral if there is unbalanced load or harmonic load.
It is always nice to have a symmetrical arrangement with the neutrals, so T for a trefoil, N for a neutral if you were to have four neutrals then on each layer you would have:
T N T N T
Sounds a bit explosive!