DC Voltage Drop Calculator

For battery bank to inverter runs, 3% is the smart target — that's the line where your inverter still has clean DC under load and your battery isn't doing extra work to compensate. 5% is acceptable on shorter accessory runs (lights, fans, fridge). Anything past 10% on a 12V system means real losses you'll feel as dim lighting, undersized inverter output, and shortened battery cycle life. The math is unforgiving at 12V because every 0.12V is another 1%.

Battery-to-inverter runs carry the highest current in the whole system, often 100A+ at full load. Use the calculator with the inverter's peak DC input current (continuous watts ÷ 12V), the round-trip distance, and a 3% threshold. For a 2000W inverter at 12V, that's ~167A continuous on copper that needs to be 2/0 AWG or larger for a 5-foot run. CCA is not acceptable here — under that current, it overheats and fails. Use only fine-stranded marine-grade copper.

You're hitting voltage drop. LED strips draw current along their full length, so the LEDs near the power supply see ~12V and the LEDs at the far end see whatever's left after resistance eats the rest. A 16-foot run of 22 AWG strip at 4A pulls roughly 0.8V on the wire — that's enough to visibly dim the end. Fix: feed power to both ends, or run a heavier 12-volt pair to the midpoint, or step up to a 24V strip system that tolerates drop better.

For DC voltage drop, no — stranded and solid copper of the same AWG have effectively the same resistance per foot. The "use stranded for flex, solid for fixed runs" rule is about mechanical fatigue and termination, not electrical performance. Where the math does change is CCA (copper-clad aluminum) versus solid copper: CCA carries roughly 55–60% more resistance for the same gauge, which on a 12V circuit can push a passing run into failing territory.

Yes, but the math matters. When 4 cameras share one 18 AWG home-run, the cable carries the total current of all 4 cameras (~3A combined for typical IR domes) plus the round-trip distance. The cable's resistance acts on the cumulative current, so the run that passed for one 0.7A camera will fail for four. Use the calculator's multi-device mode to model the actual cumulative drop, or split the cameras across separate home-runs if you're close to the threshold.

Most 600 lb mag locks pull 0.5A continuous; 1200 lb locks pull 0.75A. With 18 AWG stranded copper at 0.5A and a 5% threshold (0.6V max drop), the practical limit is around 95 feet one-way. Switch to 16 AWG and you get to ~150 feet. Past that, run 14 AWG or move the power supply closer. Critical detail: if your AHJ requires the lock to release within a specific time after fire alarm trip, the voltage at the lock matters not just for hold but for clean release timing.

Copper resistance climbs about 0.4% for every degree Celsius above the 75°C reference. Cable in a Florida attic in August can sit at 60°C ambient, which is roughly 14% higher resistance than the spec sheet shows. The calculator includes a temperature input so you can model worst-case-day performance — for outdoor security camera runs, conduit in direct sun, or RV/marine cables routed near engines, it's the difference between a passing calc and an unexpected brownout.

If the cable path is fixed (existing conduit, building layout, conduit fill limits), upsizing is your only lever. Going from 14 AWG to 12 AWG cuts resistance by ~37%. Going from 16 to 12 cuts it by 60%. If you have flexibility in equipment placement, shortening the run is almost always cheaper than thicker cable — moving a camera PSU 30 feet closer to the cluster eliminates the problem without buying heavier gauge. For battery-to-inverter, shortening is rarely an option, so wire size carries the whole load.