I was looking up SWA cable dimensions myself recently.
When I googled SWA cable I found quite a few tables from different manufacturers quoting different sizes for their products.
There were quite a few 'overlaps' - some manufacturer's 3 core 6mm cable has a larger OD than another manufacturer's 3 core 10mm etc.
yeah, it depends how thick the insulation packing and sheath are, also it seems to me that modern SWA is thinner than old stuff.
also for some sizes you can get both round and shaped conductors, i'm pretty sure shaped starts being availible at 25mm but i'm not sure when round stops being availible.
the only reliable ways to size cables are either by reading what is printed on the sheath or by disconnecting them and checking the bare core (note: unless you are very good at this you will probablly need either another cable to compare to or a verniar caliper, rememer you will need to convert your measurement from diameter to CSA)
I don't know about lots of sample cables, a short piece of 4mm, 6mm, 10mm and poss 16mm is all that you'd probably need. Working it out from Pi R² will need you to work out an individual strand (theres likely gonna be 7 strands) of copper and multiply the area by 7.
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