Calculate the minimum wire cross-section for DC circuits on vessels from load wattage, wire run length and allowable voltage drop.
Enter load, voltage and wire length to calculate.
Copper resistivity 0.0175 Ω·mm²/m. Total circuit length = 2 × one-way length (positive + negative). Per AS/NZS 3004.2.
AS/NZS 3004.2 recommends a maximum 3% voltage drop for general DC circuits on vessels. For critical safety systems (bilge pumps, navigation lights, VHF radio), keep voltage drop to 2% or less. A 3% drop on a 12V system means no more than 0.36V loss from battery to load.
DC circuits require both a positive and a negative (return) conductor. The total circuit length for resistance and voltage drop calculations is twice the one-way (run) length. For example, a 5m cable run from battery to load uses 10m of total conductor length in the calculation.
Standard automotive cable is not suitable for marine use. Marine-grade tinned copper cable is required by AS/NZS 3004.2 to resist the corrosive salt-air environment. Tinned conductors and moisture-resistant insulation prevent corrosion that can cause high-resistance connections and fire risk.