Says who? BS7671 doesn't say anything other than it needs to be sized according to load. If you think about it, our national network of Pylons that run for hundreds of miles invariably use Aluminium at 400kv/275kv, and they're flexing and stretching in the wind, heat and cold all the time... why would small diameter be different?I'd be more concerned at the fatigue life of the cable rather than it's current carrying capacity. Aluminium is fine for fixed rigid cables, it is not really suitable for small diameter flexible cables.