The question arose recently of British wire sizes and stranded vs. solid conductors.
There is an old British standard known as SWG (Standard Wire Gauge), which works in a similar way to AWG, i.e. larger numbers are smaller wires, but there is no direct correlation between the two. Although SWG was common in radio work, it was not used for electrical cables.
The old cable sizes were specified by a number such as 7/.029 where the first part is the number of strands and the second is the diameter of each strand in inches. All but the smallest standard size were stranded and the strands were tinned.
Standard sizes for applications up to about 100A were: 1/.044, 3/.029, 3/.036, 7/.029, 7/.036, 7/.044, 7/.052, 7/.064, 19/.044, 19/.053, 19/.064. For residential the 1/.044 and 3/.029 sizes were common for lights, with 7/.029 being the usual for our ring circuits and others sized as needed. Although now considered obsolete by the IEE, many of these are still in service.
Since 1970, cables have been made to metric specifications with the size quoted as the cross-sectional area in square millimeters. Standard smaller sizes are 1, 1.5, 2.5, 4, 6, 10, 16, 25 sq. mm. and the conductor is bare copper, not tinned.
In our equivalent of NM-type cable, sizes 1, 1.5 and 2.5 are solid, 4 mm and above are stranded (7 strands for the sizes listed above). The ground wire is one size smaller than the other conductors in all but the 1 sq. mm size.
Single csbles for use in conduit (or for bonding etc.) are similar, except that the 2.5 size is available as both solid and stranded. 2.5 is the usual for our ring circuits now, and is just a fraction larger than #14 AWG.
In general, the metric cables are slightly smaller overall than their Imperial equivalents, but are much harder to work and form, especially given the tight dimensions of many British fixtures and devices.
It's interesting to note that when the change to metric cables was announced, the IEE removed all references to the older standard sizes from the Regs. In my view, this was the wrong move, because even 30 years later somebody might still need to know the ratings of one of those older cables still in service. (Fine if you have a pre-1970 copy of the Regs., of course, but otherwise you have problems.)
