R1 + R2 calculator
Calculate R1 + R2 for standard copper conductor sizes, or from your own resistance per kilometre.
Result
R1 + R2– – –
Enter your values and press Calculate result.R₁ + R₂ = r₁L₁ ÷ 1,000 + r₂L₂ ÷ 1,000Standard sizes use the maximum resistance at 20 °C that BS EN 60228 allows for plain copper class 1 (solid) and class 2 (stranded) conductors, so real cable usually measures slightly lower. Flexible (class 5) and tinned conductors have higher resistance and need their own data. The 70 °C option applies the 1.20 multiplier from On-Site Guide Table I3 for a protective conductor inside the cable or bunched with cables, such as twin and earth; a separate CPC not bunched with cables uses a different factor. Two uniform conductors in series: the same circuit length for standard sizes, separate lengths in your own Ω/km mode. Joints, parallel earth paths, spurs and reactance are excluded. No ring-circuit relationship, Zs limit or compliance assessment is applied.
What the numbers mean
Resistance per kilometre multiplied by length in kilometres gives each conductor's resistance; R1 + R2 is their sum. At 20 °C the result is what a continuity test at room temperature should approach. For design checks against Table 41.3, the IET's On-Site Guide multiplies by 1.20 for thermoplastic cable running at 70 °C.
Formula reference: Eland Cables · Conductor resistance to BS EN 60228 (datasheet) ↗A worked example
A 20 m run of 2.5 mm² line conductor with a 1.5 mm² CPC: (7.41 + 12.1) Ω/km × 20 m ÷ 1,000 = 0.3902 Ω at 20 °C, or 0.46824 Ω at 70 °C.
Validation, precision and limitations