Stranding Counts and Diameters Chart -Metric mm2, AWG, kcmil, MCM, from IEC 60228/BS 6360 Conductors for insulated cables

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# IEC mm2 and AWG do not match up well, so depending on the application the size may need to be upsized if AWG falls short of the mm2 size and vise versa. MCM & kcmil are the same.

## The number of strands to IEC 60228/BS 6360 Rigid (r) stranding classes 1 & 2 is mandatory.

### Stranding counts shown in Flex (f) stranding classes 5 & 6 may have less strands if resistance Ohm/km is maintained.

#### The strand diameters in the standard are maximum and may be reduced in practice where strand size and count meet the Ohm/km.

Theoretical IEC standard versus actual calculated mm2 sizes therefore vary more then rounding errors, based on the formula Gauge mm2 = strand count x strand diameter2*PI*0.25

So, provided that the conductor does not exceed the resistance figures shown, the wire can meet the standard.

It appears that the maximum strand size for Flex (f) classes 5 and 6 are mostly several percent over the needed size to allow for tolerances and rounding of decimals which on a fine strand are more significant.

AWG sizes are governed by total cross sectional area so are easier to check using strand counts and strand diameter which gives the maximum resistance in ohms/km that is permissible for non-tinned copper conductors using a standard copper conductivity.

In both cases, IEC and AWG / kcmil systems, the actual conductivity of the copper is not easy to check by user so use of IEC and UL rated cables under factory inspection on all specs is the best way to assure actual conductivity Ohm/km per wire gauge. More about the conductivity of ASTM B3 copper wire may be found here https://www.copper.org/publications/newsletters/innovations/1997/12/wiremetallurgy.html

Tinned wires of the same diameter & copper conductivity have slightly more resistance Ohms/km since tin is not as conductive as copper, but is better at making contact versus oxidized copper, popular on fine stranded wires for marine, locomotive, mining or other harsh corrosive environment.