Per metre, Steel wire armoured cable has a lower cost than heavy-duty rubber flexible cable. 6mm 3C SWA £ 3.85 & HO7RNF £ 4.55

max unsupported span is less with all-copper of course, but if you have a catenery wire already that is not an issue, and it is certainly done to fly HO7 and similar flexible cables for temporary sites like festivals and army camps,,, Mind you T and E usually lasts a decade or two in the UK as well, its not really sunny enough to degrade very fast.

M

What does the H07 manufacturer say about the sheath's UV resistance, etc.? All else being equal back should be better than other colours (which presumably the H07-RN is, as I'm never seen anything else) but I'm less sure about rubber vs PVC for permanent use outside. It's a slightly different situation to say outdoor extension leads that would typically be moved (and hence inspected) on a regular basis, may spend a lot of time in storage rather than outside, and general bashing about possibly means they don't have the expected service life of a permanent installation.

   - Andy.

Just to add to this, it's worth bearing in mind that H07RN-F has a maximum operating temp rating of 60 degrees Celsius when fixed or flexed.

A few cabling manufacturers require a "fixed protected installation" to permit the higher operating temp of 70 degrees (assuming you'll need to achieve compliance with 512.1.5 of BS 7671).

Yes, the cable is out of reach and it's likely that the cable temp will be low BUT I do think it's worth bearing in mind.

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.

Sadly most of the manufacturers of split con dont list span data anymore but this WPD document OH4K_1-2.pdf says single phase services up to 30m are OK for concentric.  They are probably talking Al central core.  I think (and it was some time ago ) that 16mm2 was OK up to 23m with a suitable sag.  If you are stuck you could ask the manufacturers they will still have the data somewhere.