Low-voltage direct current (DC) electrical circuits in camper vans, RVs, marine vessels, and off-grid solar battery systems carry high currents, making them particularly vulnerable to resistive voltage drop. Excessive voltage drop reduces inverter efficiency, dims DC lighting, and can cause battery chargers and appliances to shut down prematurely.

This engineering sizer models voltage drop and copper conductor resistance for 12V, 24V, and 48V DC systems across American Wire Gauge sizes from 14 AWG to 4/0 AWG. It calculates round-trip conductor resistance (accounting for both supply and return legs), voltage drop in volts, percentage loss, power dissipated as heat in watts, and operating voltage delivered at the load.

For example, running a 12V DC circuit at 30 amps across a 15-foot one-way distance (30-foot round trip) using 8 AWG copper wire results in a 0.57V drop (4.71% drop) and 16.96W of power loss, leaving 11.43V at the load. Because 4.71% exceeds the recommended National Electrical Code (NEC) 3% limit for critical circuits, upgrading to 6 AWG or 4 AWG is recommended.

All circuit calculations execute locally in your web browser using standard copper conductor resistance values at 20°C. No system schematics or electrical designs are sent to any server.