ABYC E-11 Marine DC Wire Sizing

ABYC E-11 sizes on the ROUND-TRIP length (out and back), CM = 10.75 x current x (2 x length) / V_drop, not the NEC one-way habit -- and the marine allowable drop is stricter where it matters, 3% for panelboard feeders and nav/critical loads (10% non-critical). A 20 A nav feeder, 25 ft one-way, 12 V, 3% has only 0.36 V of headroom -> 29,861 circular mils -> #4 wire (#6 falls short); relax to 10% non-critical and it drops to 8,958 CM -> #10, three sizes smaller. The ABYC ampacity table sets a separate floor the drop size must clear. A design aid; the standard, wire temperature rating, and installation govern.

V_drop = drop_pct/100 x system_voltage; CM = 10.75 x current x (2 x length) / V_drop; AWG = smallest standard size with circular-mil area >= CM.

The ABYC E-11 (AC & DC Electrical Systems on Boats) DC conductor sizing by voltage drop, on the round-trip length, by name; the standard, the wire's temperature rating, and the installation govern.

The circular-mils-by-voltage-drop relation is a published ABYC E-11 method; the current, run, voltage, and allowable drop come from the circuit and the standard.

Estimate. AHJ and licensed professional govern.

Field names used by the API: current_a, run_length_ft, system_voltage_v, drop_pct, v_drop_v, circular_mils

• Round trip the length is doubled (out and back), unlike the NEC one-way habitABYC E-11
• Allowable drop 3% for panelboard feeders and critical loads, 10% for non-criticalABYC E-11
• Ampacity floor the ABYC ampacity table with engine-space and bundling derates sets a separate floorABYC E-11