Wire size & DC voltage drop

Results update as you change an input. Choose AWG or metric area; both size drafts are retained when switching modes. AWG includes 4/0, 3/0, 2/0, 1/0 and 1–40, with indices −3, −2, −1 and 0 for the four largest sizes. Metric mode uses the entered conductor area directly. Reset restores the initial wire and circuit values.

The remaining voltage is the supply voltage minus the cable drop. If the calculated drop exceeds the supply, the result shows a note about the assumed current instead. Geometry and losses lists each conductor’s voltage drop.

AWG geometry uses d = 0.127 × 92^(36−n)/39 mm and A = πd²/4. Metric diameter is √(4A/π): an equal-area solid circle, not insulation or strand-bundle diameter. The continuous inverse index is n = 36 − 39 ln(d/0.127)/ln(92). It is a geometric comparison, not a standard wire selection. The geometric progression is described in NBS Handbook 100 (1966), section 2.2. Formula values are unrounded; historical nominal manufacturing tables use rounded dimensions.

Enter the physical forward and return conductor lengths separately. Both use the same material and area: L = Lforward + Lreturn, R = ρL/A, ΔV = IR, loss = I²R. The percentage is 100ΔV divided by the entered supply. Zero current or zero total length gives zero drop and loss. If ΔV exceeds the supply, the entered current is not an operating solution for a passive load at that supply; the arithmetic is still shown.

At 20 °C, standard annealed copper (100% IACS) uses ρ = 1/58 Ω·mm²/m (NBS Handbook 100 (1966), IEC appendix). EC-H19 aluminium uses 0.028264 Ω·mm²/m, approximately 61% IACS (NBS Handbook 109 (1972), table 1). Other alloys and temperatures differ. This DC model excludes heating feedback, contacts, AC effects and current-carrying ratings; it gives no installation or safe-current approval.

Calculation limits: area 0.001–1000 mm², each length 0–100000 m, current 0–10000 A, supply 0.001–1000000 V. Fractions are accepted. These are arithmetic limits, not safety limits. Only raw inputs are stored locally, including invalid drafts and the inactive size mode; no computed results are saved.