I've already put in way too much thought and spent way too long admiring it, so now you can join me
Apart from being inch-based, BS 2004 was perhaps the best of the standards for fixed wiring sizes, as it made the most core sizes from fewer strand sizes, and generally used more/finer strands than its counterparts. Americans and Continental Europeans know nothing of it, but we did use it in Australia pre-metrication.
Its most-distinct feature was the use of 3-strand arrangements in two of the small sizes (where others go straight from a solid core to 7 strands); although 3 strands pack less efficiently into the enclosing circle than 7 (and much less efficiently than a solid core), this was no big deal at the small absolute sizes.
It happens that most of the sizes can be comfortably converted to nearby metric intervals (and the progression even becomes smoother), so here I've done it:
- 1mm² – 1/1.13 (same as IEC, although many countries start fixed wiring at 1.5mm²)
- 1.3mm² – 3/0.74
- 2mm² – 3/0.92
- 3mm² – 7/0.74
- 4.7mm² – 7/0.92
- 7mm² – 7/1.13
- 10mm² – 7/1.35 (same as IEC)
- 14mm² – 7/1.6 (also Japanese standard)
- 19mm² – 19/1.13
- 27mm² – 19/1.35 (this size exists in Australia although classified as 25mm²; in the UK you can now get a 19/1.28, true 25mm²)
- 38mm² – 19/1.6 (also Japanese standard)
- 48mm² – 19/1.8
- 60mm² – 19/2.0 (also Japanese standard)
- 74mm² – 37/1.6
- 94mm² – 37/1.8
- 116mm² – 37/2.0 (within tolerance for IEC 120mm²)
- 146mm² – 37/2.24 (or 37/2.25 as for IEC 150mm²)
- 185mm² – 37/2.52 (same as IEC)
- 240mm² – 61/2.24 (or 61/2.25 as for IEC 240mm²)
- 300mm² – 61/2.52 (same as IEC)
- 360mm² – 61/2.75 or 91/2.24 (the latter corresponds to BS 2004, but to me it felt nicer placing the 61-to-91 change across the bigger interval)
- 450mm² – 91/2.52
- 540mm² – 91/2.75 (deliberate change; BS 2004 goes to 127 smaller strands, but that combination produces a baby-step in the area increment)
- 630mm² – 127/2.52 (preferred, as used in some Australian cables) or 91/3.0 (same as IEC)
- 750mm² – 127/2.75
- 900mm² – 127/3.0 (you could jump up to 169 strands if you absolutely need a 1200mm², but the formal scope ends here)
Sizing flexible cords to match is allowed but not required (BS 2004 itself had different flex sizes).
Granted, this theoretical superiority would be insufficient to justify the major logistical costs of a changeover; and compacted conductors can have other strand counts anyway. Fortunately, Australian Standard amendments restored much of BS 2004's easier workability (stranded 1.5mm², 2.5mm² and all earths; 19 strands in 25mm² and 35mm²; 95mm² can be 37/1.78, although Prysmian cheap it out a bit with 19/2.45 instead of the normal 19/2.52
).Inkscape SVG drawings are attached below; these require the Fira typeface (install the complete set including Condensed).
I've put them into Australian-style cable designs, as British-style would be virtually indistinguishable from the original BS 2004.
(Some texts now off-page used Source Sans Pro, which I've ditched lately as it felt like an uncanny-valley between humanist and grotesque typeface designs. Not as bad as Arial though; and our award badges still seem to get away with using it, so I've left them alone.)
