Voltage Drop Calculator

How it works

R per metre = ρ (1 + α (T − 20 °C)) / A
DC / single-phase:  ΔV = 2 × L × I × R      (out and back)
three-phase:        ΔV = √3 × L × I × R     (line to line)

L is the one-way run length. Resistivity: copper 1.724 × 10⁻⁸ Ω·m, aluminium 2.82 × 10⁻⁸ Ω·m at 20 °C. A cable at its 70 °C rating has about 20 % more resistance, which the temperature field accounts for.

AWG sizes use the standard definition, d = 0.127 mm × 92^((36 − n)/39).

Limits

The calculation is resistive only. For large AC cables (above ≈ 50 mm²) reactance adds to the drop; use the cable maker’s mV/A/m tables there.

References

• American wire gauge — Wikipedia