I have been looking at "Tri-rated wire". This is wire that ostensibly meets the British BS6231 Type CK, US UL 758 Style 1015, and Canadian CSA 22.2.
I have noticed that the metric wire size (mm²) and imperial size (AWG) do not match properly. I know that there can never be an exact match, but they differ a lot.
For example, I have some wire that has both "0.75mm²" and "20AWG" printed on the wire. A search online shows that 20AWG is about 0.52mm². That is almost down to the metric 0.5mm² wire size. A closer gauge is 19AWG, though that is still off by about 0.1mm².
I have other wire that has both "1.00mm²" and "18AWG" printed on the wire. Again, they do not match - 18AWG is about 0.82mm². 17AWG is much closer to 1mm² (1.0378mm²).
I have looked at both the US and British standards, and I can see no mention of this discrepancy. I also looked at the relevant harmonised standard (EN 50525) which also does not seem to mention it.
Which measurement can I trust? Is there a prescribed way of interpreting the measurements? Is it down to the manufacturer? Are wires with metric measurements always metric, with the AWG being a rough guide?
Here is an image of the 0.75mm² wire: