Thanks all for the thoughts overall I agree that SWA is probably the better solution. I was looking at other options as it's a TT earth and from my quick look at a very messy incoming supply area I think there is a reasonable chance that non of the submains had RCD protection. There were 10 to 15 enclosures, most with metal lid's that I couldn't access easily on the initial visit. I didn't see anything that was obviously an RCD.

Owner agrees it all needs rework, but wanted that as a future project, hence considering a sub main cable that I could use without RCD protection, but maybe the steel catenary means I need RCD protection anyway. Life would have been much easier if the customer hadn't cut the existing twin + earth, I would have been comfortable continuing to use it with a  comment on the certificate. Now whatever happens we are looking at having to get something like a HIAB in to enable replacement of the cable.

Clearly need to go back to site to look a bit more closely at the incoming area and many other things.

if you have to hire a cherry picker to replace it you might be better abandoning the catenary and using split concentric which can self support over reasonable spans. There are a few threads on here that discuss the limitations of this cable but its lightweight and relatively inexpensive.  If you do go this way get a couple of preform wire 'dead ends' to support it.

Thanks for the idea. The span is in the region of 20 meters, don't see avoiding the catenary as an option.

20m is quite a span unless the cable is quite chunky- what copper cross-section would you be looking at ?

Mike

Not quite sure at the moment, trying to pin customer down on max demand. If the total cable run is 25m with 60 amps, looks like I can get away with a 10mm cable, which gives a 3.07% voltage drop. Clearly need to do some actual measurements on length of run. Given the number of other buildings running on a 100 amp single phase supply even this is pushing our luck with the main supply fuse.

Not quite sure at the moment, trying to pin customer down on max demand. If the total cable run is 25m with 60 amps, looks like I can get away with a 10mm cable, which gives a 3.07% voltage drop. Clearly need to do some actual measurements on length of run. Given the number of other buildings running on a 100 amp single phase supply even this is pushing our luck with the main supply fuse.