There are no R1 + R2 values for any cables in the regs, as that is determined by a formula that contains length so you either need to measure or calculate it.
1/ Resistivity of the steel wire
2/ Length and csa of steel wire
3/ Ambient temperature correction factors, usually stated at 20 deg C
4/ Running temperature of the cable usually stated at 30 deg C
5/ Operating temperature of cable , usually 90 Deg C or 70 deg C depending on XLPE or PVC, respectively
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