Just for fun: Create your own wire gauge

[LongRunner]

And see if you can do a better job at it than the existing systems do — which is quite possible. Of course, actually having your scheme implemented would be a perhaps unrealistic expectation, but you can never quite be sure what people will do in the future.

My idea is a logarithmic system that works in a similar way to AWG, but with the cross-sectional area aligned to "round" numbers in metric. I would set the precision at 20 steps per decade (of cross-sectional area), though I would expect all but the most demanding applications to use increments of either 2 or 3 at a time. The reference point, 1mm², would be defined as size 0, while smaller wires would have negative numbers and larger ones positive.

Oh, you want an actual name for it? Try "Future Wire Gauge" (FWG). For mains cables under this system, I might try the following sequence:

Size numbers — –6, –3, 0, +3, +6, +8, +10, +12, +14, +16, +18, +20, +22, +24, +26, +28, +30, +32, +34…
CSA (mm² rounded) — 0.5, 0.7, 1.0, 1.4, 2.0, 2.5, 3.2, 4.0, 5.0, 6.3, 7.9, 10, 13, 16, 20, 25, 32, 40, 50…
Approximate free-air ampacity* — 6.0, 7.5, 10, 13, 17, 20, 24, 28, 33, 40, 47, 56, 67, 79, 95, 112, 133, 158, 188…

*Using the reference point of 10A for 1.0mm², and assuming that the ampacity co-relates to CSA^0.75 — which could be off slightly in practice, but is closer to reality than any other "simple" calculation. (For some reason not clear to me, 0.5mm² flexible cord is supposedly only good for 3A. The other thing about it, I believe, is that it is only available with light-duty insulation and sheathing.)

[c_hegge]

I dont really see the need for wire gauges. Just go by the diameter or other size.

[LongRunner]

That's possible, but I only know a pretty small set of standard metric sizes (…0.5, 0.75, 1.0, 1.5, 2.5, 4, 6, 10, 16, 25…), which is fine for hook-up wiring but not really good enough for optimisation of inductive components. Plus, to precisely follow a logarithmic, 5-values-per-decade sequence, 1.5mm² should actually be 1.6mm² and 6mm² should be 6.3mm².

An alternative metric range could be to adapt the E-series of passive component values to wire sizes. E24 would probably be the one to use as the base, though hook-up wires would just use E6, E12 or perhaps a hypothetical E8.

For example:

E6 sequence (mm² rounded) — 0.47, 0.68, 1.0, 1.5, 2.2, 3.3, 4.7, 6.8, 10, 15, 22, 33, 47…
Approximate free-air ampacity* — 5.5, 7.5, 10, 14, 18, 25, 32, 42, 56, 76, 102, 138, 180…

*Again using 10A for 1.0mm² as the reference point and CSA^0.75 to extrapolate.

Logical much? The idea of my system presented above is to be both more intuitive than AWG and more flexible (?) than the standard metric size set. For hook-up wiring the difference between 0.71mm² (–3 FWG) and 0.75mm² (standard metric) may be pretty cosmetic, but for optimising a transformer it could be a make-or-break affair (with "make" for the slightly smaller size, which will actually fit into the unit instead of pushing the physical boundaries and forcing the next size down to be used) — so I believe a true logarithmic system is the way to go.